%%% Please DO NOT EDIT this file - it was automatically generated.
%%% Technical reports from the Department of Information Technology,
%%% Uppsala University, Sweden.
%%% Series ISSN 1404-3203 (1404-0603 up to and including 1999-006).
%%%
%%% ====================================================================
%%% BibTeX-file{
%%% author = "Bj{\"o}rn Victor",
%%% date = "05 May 2020",
%%% filename = "itreports.bib",
%%% url = "http://www.it.uu.se/research/publications/reports/itreports.bib",
%%% www-home = "http://www.it.uu.se/research/publications/reports/",
%%% address = "Department of Information Technology,
%%% Uppsala University,
%%% Box 337,
%%% SE-751 05 Uppsala, SWEDEN",
%%% telephone = "+46 18 471 0000",
%%% FAX = "+46 18 511925",
%%% email = "Bjorn.Victor at it.uu.se",
%%% dates = {1999--},
%%% keywords = "",
%%% supported = "yes",
%%% supported-by = "Bj{\"o}rn Victor",
%%% abstract = "Technical reports from the Department of
%%% Information Technology at Uppsala University"
%%% }
%%% ====================================================================
@PREAMBLE{ "\usepackage{amssymb}" }
@STRING{cb = "Centre for Image Analysis" }
@STRING{csd = "Computing Science Division" }
@STRING{docs = "Division of Computer Systems" }
@STRING{hci = "Division of Human-Computer Interaction" }
@STRING{it = "Department of Information Technology, Uppsala University" }
@STRING{mdi = "Division of Human-Computer Interaction" }
@STRING{syscon = "Division of Systems and Control" }
@STRING{tdb = "Division of Scientific Computing" }
@STRING{vi2 = "Division of Visual Information and Interaction" }
@TechReport{ it:2020-002,
author = {Owe Axelsson and Michal B{\'e}res and Radim Blaheta},
title = {A Boundary Optimal Control Identification Problem},
institution = it,
department = tdb,
year = 2020,
number = {2020-002},
month = may,
abstract = {Optimal control methods are applied in various problems
and can be efficient also for solving inverse problems,
such as parameter identification and boundary control which
arise in many important applications. For boundary optimal
control methods one can identify conditions on an
inaccessible part of the boundary by letting them play the
role of a control variable function and by overimposing
boundary conditions at another part of the boundary of the
given domain.
The paper shows a mathematical formulation of the problem,
the arising (regularized) Karush-Kuhn-Tucker (KKT) system
and introduces a preconditioner for this system. The
spectral analysis of the preconditioner and numerical tests
with preconditioning are included.}
}
@TechReport{ it:2020-001,
author = {{\AA}sa Cajander and Marta Larusdottir and Gustaf
Hedstr{\"o}m},
title = {Digital arbetsmilj{\"o} och projektet N{\"a}ra v{\aa}rd
online},
institution = it,
year = 2020,
number = {2020-001},
month = mar,
abstract = {Denna rapport inneh{\aa}ller en kartl{\"a}ggning av
1177-personalens digitala arbetsmilj{\"o} vid arbete med
den chattfunktion till patienter som anv{\"a}ndes under ett
pilotprojekt h{\"o}sten 2019. Rapporten {\"a}r skriven med
utg{\aa}ngspunkt fr{\aa}n att l{\"a}saren har inblick i
personalen p{\aa} 1177s arbete, och har kunskap kring de
IT-system som anv{\"a}nds. Kartl{\"a}ggningen
genomf{\"o}rdes som ett samarbete mellan
forskningsprojektet Systemutvecklingsmetoder f{\"o}r
digital arbetsmilj{\"o} som leds av Uppsala Universitet och
Region Uppsalas projekt N{\"a}ra V{\aa}rd Online under
h{\"o}sten och vintern 2019/2020.
Kontextuella intervjuer genomf{\"o}rdes p{\aa} plats under
cirka fem timmar. Dessutom genomf{\"o}rdes nio
semistrukturerade intervjuer med sjuksk{\"o}terskorna och
{\aa}tta med l{\"a}kare. Intervjufr{\aa}gorna grupperades i
fyra teman: intervjupersonens bakgrund; arbetsmilj{\"o}
relaterat till pilotprojektet; arbetsmilj{\"o} relaterat
till det {\"a}ldre s{\"a}ttet att arbeta och n{\aa}gra
avslutande fr{\aa}gor. Alla intervjuer transkriberades och
tematisk analys gjordes.
Inom temat upplevelse av \textbf{krav} visar intervjuerna
att det som {\"a}r mest stressande, och som n{\"a}stan
stressar alla, {\"a}r k{\"o}bildningen i chattsystemet. Det
som stressar {\"a}r otillr{\"a}cklig information om vilka
samtal som v{\"a}ntar, och att man inte kan veta n{\"a}r
personen man chattar med svarar. Dessutom p{\aa}pekar
n{\aa}gra att man inte heller kan se vilka patienter som
beh{\"o}ver snabb hj{\"a}lp och vilka som kan v{\"a}nta.
Inom temat \textbf{st{\"o}d} kan man konstatera att alla
upplever systemen som stabila, och har god inblick i vad
man kan g{\"o}ra om systemen inte fungerar. M{\aa}nga
tycker att systemen fungerar mycket bra. N{\aa}gra
p{\aa}pekar att samarbetet och st{\"o}det fr{\aa}n kollegor
som jobbar hemifr{\aa}n inte fungerar lika bra som att
arbeta p{\aa} samma plats.
Inom omr{\aa}det upplevelse av \textbf{kontroll} finns det
f{\"o}rb{\"a}ttringsomr{\aa}den vad det g{\"a}ller vilka
fr{\aa}gor som patienten svarat p{\aa}, och
sjuksk{\"o}terskor p{\aa}pekade att systemet delvis {\"a}r
designat f{\"o}r l{\"a}kare och inte f{\"o}r
sjuksk{\"o}terskors arbete. M{\aa}nga upplevde att de kunde
vara med och p{\aa}verka i f{\"o}r{\"a}ndringsarbetet, och
att de i mycket stor utstr{\"a}ckning varit delaktig.
Rapporten inneh{\aa}ller ocks{\aa} n{\aa}gra
rekommendationer kring design och implementering av
liknande tj{\"a}nster ur ett arbetsmilj{\"o}perspektiv. Slutligen finns l{\"a}stips f{\"o}r den intresserade l{\"a}saren. }
}
@TechReport{ it:2019-011,
author = {Pietro Benedusi and Paola Ferrari and Carlo Garoni and
Rolf Krause and Stefano Serra-Capizzano},
title = {Fast Parallel Solver for the Space-Time {IgA-DG}
Discretization of the Anisotropic Diffusion Equation},
institution = it,
department = tdb,
year = 2019,
number = {2019-011},
month = nov,
abstract = {We consider the space-time discretization of the (linear)
anisotropic diffusion equation, using an isogeometric
analysis (IgA) approximation in space and a discontinuous
Galerkin (DG) approximation in time. Drawing inspiration
from a former spectral analysis, we propose for the
resulting space-time linear system a new solution method
combining a suitable preconditioned GMRES (PGMRES)
algorithm with a few iterations of an appropriate multigrid
method. The performance of our new solution method is
illustrated through numerical experiments, which show its
competitiveness in terms of robustness, run-time and
parallel scaling.}
}
@TechReport{ it:2019-010,
author = {Umberto Soverini and Torsten S{\"o}derstr{\"o}m},
title = {The {F}risch Scheme: Time and Frequency Domain Aspects},
institution = it,
department = syscon,
year = 2019,
number = {2019-010},
month = nov,
abstract = {Several estimation methods have been proposed for
identifying errors-in-variables systems, where both input
and output measurements are corrupted by noise. One of the
more interesting approaches is the Frisch scheme. The
method can be applied using either time or frequency domain
representations. This paper investigates the general
mathematical and geometrical aspects of the Frisch scheme,
illustrating the analogies and the differences between the
time and frequency domain formulations.}
}
@TechReport{ it:2019-009,
author = {Kristiina Ausmees},
title = {Evaluation of Methods Handling Missing Data in {PCA} on
Genotype Data: Applications for Ancient {DNA}},
institution = it,
department = tdb,
year = 2019,
number = {2019-009},
month = oct,
abstract = {Principal Component Analysis (PCA) is a method of
projecting data onto a basis that maximizes its variance,
possibly revealing previously unseen patterns or features.
PCA can be used to reduce the dimensionality of
multivariate data, and is widely applied in visualization
of genetic information. In the field of ancient DNA, it is
common to use PCA to show genetic affinities of ancient
samples in the context of modern variation. Due to the low
quality and sequence coverage often exhibited by ancient
samples, such analysis is not straightforward, particularly
when performing joint visualization of multiple individuals
with non-overlapping sequence data. The PCA transform is
based on variances of allele frequencies among pairs of
individuals, and discrepancies in overlap may therefore
have large effects on scores. As the relative distances
between scores are used to infer genetic similarity, it is
important to distinguish between the effects of the
particular set of markers used and actual genetic
affinities. This work addresses the problem of using an
existing PCA model to estimate scores of new observations
with missing data. We address the particular application of
visualizing genotype data, and evaluate approaches commonly
used in population genetic analyses as well as other
methods from the literature. The methods considered are
that of trimmed scores, projection to the model plane,
performing PCA individually on samples and subsequently
merging them using Procrustes transformation, as well as
the two least-squares based methods trimmed score
regression and known data regression. Using empirical
ancient data, we demonstrate the use of the different
methods, and show that discrepancies in the set of loci
considered for different samples can have pronounced
effects on estimated scores. We also present an evaluation
of the methods based on modern data with varying levels of
simulated sparsity, concluding that their relative
performance is highly data-dependent.}
}
@TechReport{ it:2019-008,
author = {Kristiina Ausmees and Federico Sanchez-Quinto and Mattias
Jakobsson and Carl Nettelblad},
title = {An Empirical Evaluation of Genotype Imputation of Ancient
{DNA}},
institution = it,
department = tdb,
year = 2019,
number = {2019-008},
month = oct,
abstract = {With capabilities of sequencing ancient DNA to high
coverage often limited by sample quality or cost,
imputation of missing genotypes presents a possibility to
increase power of inference as well as cost-effectiveness
in analysis of ancient data. However, the high degree of
uncertainty often associated with ancient DNA poses several
methodological challenges, and performance of imputation
methods in this context has not been fully explored. To
gain further insights, we performed a systematic evaluation
of imputation of ancient data using BEAGLE 4.0 and
reference data from phase 3 of the 1000 Genomes project,
investigating the effects of coverage, phased reference and
study sample size. Making use of five ancient samples with
high-coverage data available, we evaluated imputed data
with respect to accuracy, reference bias and genetic
affinities as captured by PCA. We obtained genotype
concordance levels of over 99\% for data with 1x coverage,
and similar levels of accuracy and reference bias at levels
as low as 0.75x. Our findings suggest that using imputed
data can be a realistic option for various population
genetic analyses even for data in coverage ranges below 1x.
We also show that a large and varied phased reference set
as well as the inclusion of low- to moderate-coverage
ancient samples can increase imputation performance,
particularly for rare alleles. In-depth analysis of imputed
data with respect to genetic variants and allele
frequencies gave further insight into the nature of errors
arising during imputation, and can provide practical
guidelines for post-processing and validation prior to
downstream analysis.}
}
@TechReport{ it:2019-007,
author = {Malin K{\"a}ll{\'e}n and Tobias Wrigstad},
title = {Performance of an {OO} Compute Kernel on the {JVM}:
Revisiting {J}ava as a Language for Scientific Computing
Applications ({E}xtended Version)},
institution = it,
year = {2019},
number = {2019-007},
month = sep,
abstract = {The study of Java as a programming language for scientific
computing is warranted by simpler, more extensible and more
easily maintainable code. Previous work on refactoring a
C++ scientific computing code base to follow best practises
of object-oriented software development revealed a coupling
of such practises and considerable slowdowns due to
indirections introduced by abstractions. In this paper, we
explore how Java's JIT compiler handle such
abstraction-induced indirection using a typical scientific
computing compute kernel extracted from a linear solver
written in C++. We find that the computation times for
large workloads on one machine can be on-pair for C++ and
Java. However, for distributed computations, a better
parallelisation strategy needs to be found for non-blocking
communication. We also report on the impact on performance
for common ``gripes'': garbage collection, array bounds
checking, and dynamic binding.}
}
@TechReport{ it:2019-006,
author = {Umberto Soverini and Torsten S{\"o}derstr{\"o}m},
title = {Frequency Domain Identification of {FIR} Models from Noisy
Input-Output Data},
institution = it,
department = syscon,
year = 2019,
number = {2019-006},
month = aug,
abstract = {This paper describes a new approach for identifying FIR
models from a finite number of measurements, in the
presence of additive and uncorrelated white noise. In
particular, two different frequency domain algorithms are
proposed. The first algorithm is based on some theoretical
results concerning the dynamic Frisch scheme. The second
algorithm maps the FIR identification problem into a
quadratic eigenvalue problem. Both methods resemble in many
aspects some other identification algorithms, originally
developed in the time domain. The features of the proposed
methods are compared with each other and with those of some
time domain algorithms by means of Monte Carlo
simulations.}
}
@TechReport{ it:2019-005,
author = {Giovanni Barbarino and Carlo Garoni and Stefano
Serra-Capizzano},
title = {Block Generalized Locally {T}oeplitz Sequences: Theory and
Applications in the Multidimensional Case},
institution = it,
department = tdb,
year = 2019,
number = {2019-005},
month = jul,
abstract = {In computational mathematics, when dealing with a large
linear discrete problem (e.g., a linear system) arising
from the numerical discretization of a partial differential
equation (PDE), the knowledge of the spectral distribution
of the associated matrix has proved to be a useful
information for designing/analyzing appropriate
solvers---especially, preconditioned Krylov and multigrid
solvers---for the considered problem. Actually, this
spectral information is of interest also in itself as long
as the eigenvalues of the aforementioned matrix represent
physical quantities of interest, which is the case for
several problems from engineering and applied sciences
(e.g., the study of natural vibration frequencies in an
elastic material).
The theory of multilevel generalized locally Toeplitz (GLT)
sequences is a powerful apparatus for computing the
asymptotic spectral distribution of matrices $A_n$ arising
from virtually any kind of numerical discretization of
PDEs. Indeed, when the mesh-fineness parameter $n$ tends to
infinity, these matrices $A_n$ give rise to a sequence
$\{A_n\}_n$, which often turns out to be a multilevel GLT
sequence or one of its ``relatives'', i.e., a multilevel
block GLT sequence or a (multilevel) reduced GLT sequence.
In particular, multilevel block GLT sequences are
encountered in the discretization of systems of PDEs as
well as in the higher-order finite element or discontinuous
Galerkin approximation of scalar/vectorial PDEs.
In this work, we systematically develop the theory of
multilevel block GLT sequences as an extension of the
theories of (unilevel) GLT sequences \cite{GLT-bookI},
multilevel GLT sequences \cite{GLT-bookII}, and block GLT
sequences \cite{bg}. We also present several emblematic
applications of this theory in the context of PDE
discretizations.}
}
@TechReport{ it:2019-004,
author = {Giovanni Barbarino and Carlo Garoni and Stefano
Serra-Capizzano},
title = {Block Generalized Locally {T}oeplitz Sequences: Theory and
Applications in the Unidimensional Case},
institution = it,
department = tdb,
year = 2019,
number = {2019-004},
month = jul,
abstract = {In computational mathematics, when dealing with a large
linear discrete problem (e.g., a linear system) arising
from the numerical discretization of a differential
equation (DE), the knowledge of the spectral distribution
of the associated matrix has proved to be a useful
information for designing/analyzing appropriate
solvers---especially, preconditioned Krylov and multigrid
solvers---for the considered problem. Actually, this
spectral information is of interest also in itself as long
as the eigenvalues of the aforementioned matrix represent
physical quantities of interest, which is the case for
several problems from engineering and applied sciences
(e.g., the study of natural vibration frequencies in an
elastic material).
The theory of generalized locally Toeplitz (GLT) sequences
is a powerful apparatus for computing the asymptotic
spectral distribution of matrices $A_n$ arising from
virtually any kind of numerical discretization of DEs.
Indeed, when the mesh-fineness parameter $n$ tends to
infinity, these matrices $A_n$ give rise to a sequence
$\{A_n\}_n$, which often turns out to be a GLT sequence or
one of its ``relatives'', i.e., a block GLT sequence or a
reduced GLT sequence. In particular, block GLT sequences
are encountered in the discretization of systems of DEs as
well as in the higher-order finite element or discontinuous
Galerkin approximation of scalar/vectorial DEs.
This work is a review, refinement, extension, and
systematic exposition of the theory of block GLT sequences.
It also includes several emblematic applications of this
theory in the context of DE discretizations.}
}
@TechReport{ it:2019-003,
author = {Ricardo Alves and Stefanos Kaxiras and David
Black-Schaffer},
title = {Minimizing Replay under Way-Prediction},
institution = it,
department = docs,
year = 2019,
number = {2019-003},
month = may,
note = {This paper is an extension of another paper published in
ICCD 2018 ``Dynamically Disabling Way-prediction to Reduce
Instruction Replay''.},
abstract = {Way-predictors are effective at reducing dynamic cache
energy by reducing the number of ways accessed, but
introduce additional latency for incorrect way-predictions.
While previous work has studied the impact of the increased
latency for incorrect way-predictions, we show that the
\textit{latency variability} has a far greater effect as it
forces replay of in-flight instructions on an incorrect
way-prediction. To address the problem, we propose a
solution that learns the confidence of the way-prediction
and dynamically disables it when it is likely to
mispredict. We further improve this approach by biasing the
confidence to reduce latency variability further at the
cost of reduced way-predictions. Our results show that
instruction replay in a way-predictor reduces IPC by 6.9\%
due to 10\% of the instructions being replayed. Our
confidence-based way-predictor degrades IPC by only 2.9\%
by replaying just 3.4\% of the instructions, reducing
way-predictor cache energy overhead (compared to serial
access cache) from 8.5\% to 1.9\%.}
}
@TechReport{ it:2019-002,
author = {C. Garoni and S. Serra-Capizzano},
title = {Block Generalized Locally {T}oeplitz Sequences: Theory and
Applications},
institution = it,
department = tdb,
year = 2019,
number = {2019-002},
month = apr,
abstract = {When dealing with a large linear system arising from the
numerical discretization of a differential equation (DE),
the knowledge of the spectral distribution of the
associated matrix has proved to be a useful information for
designing/analyzing appropriate solvers|especially,
preconditioned Krylov and multigrid solvers for the
considered system. The theory of generalized locally
Toeplitz (GLT) sequences is a powerful apparatus for
computing the asymptotic spectral distribution of matrices
$A_n$ arising from virtually any kind of numerical
discretization of DEs. Indeed, when the mesh-fineness
parameter n tends to infinity, these matrices $A_n$ give
rise to a sequence $\{ A_n \}$, which often turns out to be
a GLT sequence or one of its "relatives", i.e., a block GLT
sequence or a reduced GLT sequence. In particular, block
GLT sequences are encountered in the discretization of
systems of DEs as well as in the higher-order finite
element or discontinuous Galerkin approximation of
scalar/vectorial DEs. This work is a review, refinement,
extension, and systematic exposition of the theory of block
GLT sequences. It also includes several emblematic
applications of this theory in the context of DE
discretizations.}
}
@TechReport{ it:2018-014,
author = {Nikos Nikoleris and Erik Hagersten and Trevor E. Carlson},
title = {Delorean: Virtualized Directed Profiling for Cache
Modeling in Sampled Simulation},
institution = it,
department = docs,
year = 2018,
number = {2018-014},
month = dec,
abstract = {Current practice for accurate and efficient simulation
(e.g., SMARTS and Simpoint) makes use of sampling to
significantly reduce the time needed to evaluate new
research ideas. By evaluating a small but representative
portion of the original application, sampling can allow for
both fast and accurate performance analysis. However, as
cache sizes of modern architectures grow, simulation time
is dominated by warming microarchitectural state and not by
detailed simulation, reducing overall simulation
efficiency. While checkpoints can significantly reduce
cache warming, improving efficiency, they limit the
flexibility of the system under evaluation, requiring new
checkpoints for software updates (such as changes to the
compiler and compiler flags) and many types of hardware
modifications. An ideal solution would allow for accurate
cache modeling for each simulation run without the need to
generate rigid checkpointing data a priori.
Enabling this new direction for fast and flexible
simulation requires a combination of (1) a methodology that
allows for hardware and software flexibility and (2) the
ability to quickly and accurately model arbitrarily-sized
caches. Current approaches that rely on checkpointing or
statistical cache modeling require rigid, up-front state to
be collected which needs to be amortized over a large
number of simulation runs. These earlier methodologies are
insufficient for our goals for improved flexibility. In
contrast, our proposed methodology, Delorean, outlines a
unique solution to this problem. The Delorean simulation
methodology enables both flexibility and accuracy by
quickly generating a targeted cache model for the next
detailed region on the fly without the need for up-front
simulation or modeling. More specifically, we propose a
new, more accurate statistical cache modeling method that
takes advantage of hardware virtualization to precisely
determine the memory regions accessed and to minimize the
time needed for data collection while maintaining accuracy.
Delorean uses a multi-pass approach to understand the
memory regions accessed by the next, upcoming detailed
region. Our methodology collects the entire set of key
memory accesses and, through fast virtualization
techniques, progressively scans larger, earlier regions to
learn more about these key accesses in an efficient way.
Using these techniques, we demonstrate that Delorean allows
for the fast evaluation of systems and their software
though the generation of accurate cache models on the fly.
Delorean outperforms previous proposals by an order of
magnitude, with a simulation speed of 150 MIPS and a
similar average CPI error (below 4\%).}
}
@TechReport{ it:2018-013,
author = {Stanislav Morozov and Stefano Serra-Capizzano and Eugene
Tyrtyshnikov},
title = {How to Extend the Application Scope of {GLT}-Sequences},
institution = it,
department = tdb,
year = 2018,
number = {2018-013},
month = nov,
abstract = {In this paper we address the problem of finding the
distribution of eigenvalues and singular values for matrix
sequences. The main focus of this paper is the spectral
distribution for matrix sequences arising in discretization
of PDE. In the last two decades the theory of GLT-sequences
aimed at this problem has been developed. We investigate
the possibility of application of GLT-theory to
discretization of PDE on non-rectangular domains and show
that in many cases the present GLT-theory is insufficient.
We also propose a generalization of GLT-sequences that
enables one to cope with a wide range of PDE discretization
problems defined on polygonal domains.}
}
@TechReport{ it:2018-012,
author = {Sven-Erik Ekstr{\"o}m and Stefano Serra-Capizzano},
title = {Eigenvalue Isogeometric Approximations Based on
{B}-splines: Tools and Results},
institution = it,
department = tdb,
year = 2018,
number = {2018-012},
month = jul,
abstract = {In such a short note we consider the spectral analysis of
large matrices coming from the numerical approximation of
the eigenvalue problem \[ -(a(x)u'(x))'=\lambda b(x)
u(x),\quad\quad x\in (0,1), \] where $u(0)$ and $u(1)$ are
given, by using isogeometric methods based on B-splines. We
give precise estimates for the extremal eigenvalues and
global distributional results. The techniques involve
dyadic decomposition arguments, the GLT analysis, and basic
extrapolation methods.}
}
@TechReport{ it:2018-011,
author = {Tatiana Chistiakova and Per Mattsson and Bengt Carlsson
and Torbj{\"o}rn Wigren},
title = {Nonlinear System Identification of the Dissolved Oxygen to
Effluent Ammonium Dynamics in an Activated Sludge Process},
institution = it,
department = syscon,
year = 2018,
number = {2018-011},
month = jun,
abstract = {Aeration of biological reactors in wastewater treatment
plants is important to obtain a high removal of soluble
organic matter as well as for nitrification but requires a
significant use of energy. It is hence of importance to
control the aeration rate, for example, by ammonium
feedback control. The goal of this report is to model the
dynamics from the set point of an existing dissolved oxygen
controller to effluent ammonium using two types of system
identification methods for a Hammerstein model, including a
newly developed recursive variant. The models are estimated
and evaluated using noise corrupted data from a complex
mechanistic model (Activated Sludge Model no.1). The
performances of the estimated nonlinear models are compared
with an estimated linear model and it is shown that the
nonlinear models give a significantly better fit to the
data. The resulting models may be used for adaptive control
(using the recursive Hammerstein variant), gain-scheduling
control, L2 stability analysis, and model based fault
detection.}
}
@TechReport{ it:2018-010,
author = {Owe Axelsson and Maya Neytcheva},
title = {Preconditioners for Two-by-Two Block Matrices with Square
Blocks},
institution = it,
department = tdb,
year = 2018,
number = {2018-010},
month = may,
abstract = {Two-by-two block matrices with square blocks arise in the
numerical treatment of numerous applications of practical
significance, such as optimal control problems, constrained
by a state equation in the form of partial differential
equations, multiphase models, solving complex linear
systems in real arithmetics, to name a few.a
Such problems lead to algebraic systems of equations with
matrices of a certain two-by-two block form. For such
matrices, a number of preconditioners has been proposed,
some of them with tight eigenvalue bounds. In this paper it
is shown that in particular one of them, referred to as
PRESB, is very efficient, not only giving robust,
favourable properties of the spectrum but also enabling an
efficient implementation with low computational complexity.
Various applications and generalizations of this
preconditioning technique, such as in time-harmonic
parabolic and Stokes equations, eddy current
electromagnetic problems and problems with additional
box-constraints, i.e. upper and/or lower bounds of the
solution, are also discussed.
The method is based on the use of coupled inner-outer
iterations, where the inner iteration can be performed to
various relative accuracies. This leads to variable
preconditioners, thus, a flexible version of a Krylov
subspace iteration method must be used. Alternatively, some
version of a defect-correction iterative method can be
applied. }
}
@TechReport{ it:2018-009,
author = {Carlo Garoni and Mariarosa Mazza and Stefano
Serra-Capizzano},
title = {Block Generalized Locally Toeplitz Sequences: From the
Theory to the Applications},
institution = it,
department = tdb,
year = 2018,
number = {2018-009},
month = may,
abstract = {The theory of generalized locally Toeplitz (GLT) sequences
is a powerful apparatus for computing the asymptotic
spectral distribution of matrices $A_n$ arising from
virtually any kind of numerical discretization of
differential equations (DEs). Indeed, when the mesh
fineness parameter $n$ tends to infinity, these matrices
$A_n$ give rise to a sequence $\{A_n\}_n$, which often
turns out to be a GLT sequence or one of its ``relatives'',
i.e., a block GLT sequence or a reduced GLT sequence. In
particular, block GLT sequences are encountered in the
discretization of systems of DEs as well as in the
higher-order finite element or discontinuous Galerkin
approximation of scalar DEs. Despite the applicative
interest, a solid theory of block GLT sequences has been
developed only recently, in 2018. The purpose of the
present paper is to illustrate the potential of this theory
by presenting a few noteworthy examples of applications in
the context of DE discretizations.}
}
@TechReport{ it:2018-008,
author = {Owe Axelsson and Maya Neytcheva and Anders Str{\"o}m},
title = {An Efficient Preconditioning Method for State
Box-Constrained Optimal Control Problems},
institution = it,
department = tdb,
year = 2018,
number = {2018-008},
month = mar,
note = {This is a major revision of Technical Report 2017-004. In
the new version all the numerical experiments have been
rerun with new much more efficient dynamic stopping
criteria.},
abstract = {An efficient preconditioning technique used earlier for
two-by-two block matrix systems with square matrix blocks
is shown to be applicable also for a state variable
box-constrained optimal control problem. The problem is
penalized by a standard regularization term for the control
variable and for the box-constraint, using a Moreau-Yosida
penalization method. It is shown that there occur very few
nonlinear iteration steps and also few iterations to solve
the arising linearized equations on the fine mesh. This
holds for a wide range of the penalization and
discretization parameters. The arising nonlinearity can be
handled with a hybrid nonlinear-linear procedure that
raises the computational efficiency of the overall solution
method.}
}
@TechReport{ it:2018-007,
author = {Umberto Soverini and Torsten S{\"o}derstr{\"o}m},
title = {Identification of Two Dimensional Complex Sinusoids in
White Noise: a State-Space Frequency Approach},
institution = it,
department = syscon,
year = 2018,
number = {2018-007},
month = apr,
note = {Updated version of Technical Report 2017-021.},
abstract = {This paper proposes a new frequency domain approach for
identifying the parameters of two-dimensional complex
sinusoids from a finite number of data, when the
measurements are affected by additive and uncorrelated
two-dimensional white noise. The new method extends in two
dimensions a frequency identification procedure of complex
sinusoids, originally developed for the one-dimensional
case. The properties of the proposed method are analyzed by
means of Monte Carlo simulations and its features are
compared with those of other estimation algorithms. In
particular the practical advantage of the method is
highlighted. In fact the novel approach can operate just on
a specified sub-area of the 2D spectrum. This
area-selective feature allows a drastic reduction of the
computational complexity, which is usually very high when
standard time domain methods are used.}
}
@TechReport{ it:2018-006,
author = {Umberto Soverini and Torsten S{\"o}derstr{\"o}m},
title = {2D-Frequency Domain Identification of Complex Sinusoids in
the Presence of Additive Noise},
institution = it,
department = syscon,
year = 2018,
number = {2018-006},
month = apr,
note = {Updated version of Technical Report 2017-020.},
abstract = {This paper describes a new approach for identifying the
parameters of two-dimensional complex sinusoids from a
finite number of measurements, in presence of additive and
uncorrelated two-dimensional white noise. The proposed
approach is based on using frequency domain data. The new
method extends to the two-dimensional (2D) case some recent
results obtained with reference to the frequency ESPRIT
algorithm. The properties of the proposed method are
analyzed by means of Monte Carlo simulations and its
features are compared with those of a classical time domain
estimation algorithm. The practical advantages of the
method are highlighted. In fact the novel approach can
operate just on a specified sub-area of the 2D spectrum.
This area-selective feature allows a drastic reduction of
the computational complexity, which is usually very high
when standard time domain methods are used.}
}
@TechReport{ it:2018-005,
author = {Sven-Erik Ekstr{\"o}m and Isabella Furci and Stefano
Serra-Capizzano},
title = {Exact Formulae and Matrix-Less Eigensolvers for Block
Banded Symmetric {T}oeplitz Matrices},
institution = it,
department = tdb,
year = 2018,
number = {2018-005},
month = mar,
abstract = {Precise asymptotic expansions for the eigenvalues of a
Toeplitz matrix $T_n(f)$, as the matrix size $n$ tends to
infinity, have recently been obtained, under suitable
assumptions on the associated generating function $f$. A
restriction is that $f$ has to be polynomial, monotone, and
scalar-valued. In this paper we focus on the case where
$\mathbf{f}$ is an $s\times s$ matrix-valued trigonometric
polynomial with $s\ge 1$, and $T_n(\mathbf{f})$ is the
block Toeplitz matrix generated by $\mathbf{f}$, whose size
is $N(n,s)=sn$. The case $s=1$ corresponds to that already
treated in the literature. We numerically derive conditions
which ensure the existence of an asymptotic expansion for
the eigenvalues. Such conditions generalize those known for
the scalar-valued setting. Furthermore, following a
proposal in the scalar-valued case by the first author,
Garoni, and the third author, we devise an extrapolation
algorithm for computing the eigenvalues of banded symmetric
block Toeplitz matrices with a high level of accuracy and a
low computational cost. The resulting algorithm is an
eigensolver that does not need to store the original
matrix, does not need to perform matrix-vector products,
and for this reason is called {\em matrix-less}. We use the
asymptotic expansion for the efficient computation of the
spectrum of special block Toeplitz structures and we
provide exact formulae for the eigenvalues of the matrices
coming from the $\mathbb{Q}_p$ Lagrangian Finite Element
approximation of a second order elliptic differential
problem. Numerical results are presented and critically
discussed.}
}
@TechReport{ it:2018-004,
author = {Giovanni Barbarino and Stefano Serra-Capizzano},
title = {Non-{H}ermitian Perturbations of {H}ermitian
Matrix-Sequences and Applications to the Spectral Analysis
of Approximated {PDE}s},
institution = it,
department = tdb,
year = 2018,
number = {2018-004},
month = feb,
abstract = {This paper concerns the spectral analysis of
matrix-sequences which can be written as a non-Hermitian
perturbation of a given Hermitian matrix-sequence. The main
result reads as follows. Suppose that $X_n$ is a Hermitian
matrix of size $n$ and that $\{X_n\}_n\sim_{\lambda} f$,
i.e., the matrix-sequence $\{X_n\}_n$ enjoys an asymptotic
spectral distribution, in the Weyl sense, described by a
Lebesgue measurable function $f$; if $\|Y_n\|_2 = o(\sqrt
n)$ with $\|\cdot\|_2$ being the Schatten 2 norm, then
$\{X_n+Y_n\}_n\sim_{\lambda} f$.
In a previous paper by Leonid Golinskii and the second
author a similar result was proved, but under the technical
restrictive assumption that the involved matrix-sequences
$\{ X_n\}_n$ and $\{ Y_n\}_n$ are uniformly bounded in
spectral norm. Nevertheless, the result had a remarkable
impact in the analysis of both spectral distribution and
clustering of matrix-sequences arising from various
applications, including the numerical approximation of
partial differential equations (PDEs) and the
preconditioning of PDE discretization matrices. The new
result considerably extends the spectral analysis tools
provided by the former one, and in fact we are now allowed
to analyse variable-coefficient PDEs with unbounded
coefficients, preconditioned matrix-sequences, etc.
A few selected applications are considered, extensive
numerical experiments are discussed, and a further
conjecture is illustrated at the end of the paper.}
}
@TechReport{ it:2018-003,
author = {Jonatan Lind{\'e}n and Bengt Jonsson},
title = {A Skiplist-Based Concurrent Priority Queue with Minimal
Memory Contention},
institution = it,
department = docs,
year = 2018,
number = {2018-003},
month = feb,
note = {Revised and corrected version of Technical Report
2013-025.},
abstract = {Priority queues are fundamental to many multiprocessor
applications. Several priority queue algorithms based on
skiplists have been proposed, as skiplists allow concurrent
accesses to different parts of the data structure in a
simple way. However, for priority queues on
multiprocessors, an inherent bottleneck is the operation
that deletes the minimal element. We present a
linearizable, lock-free, concurrent priority queue
algorithm, based on skiplists, which minimizes the
contention for shared memory that is caused by the
\textsc{DeleteMin} operation. The main idea is to minimize
the number of global updates to shared memory that are
performed in one \textsc{DeleteMin}. In comparison with
other skiplist-based priority queue algorithms, our
algorithm achieves a 30 - 80\% improvement.}
}
@TechReport{ it:2018-002,
author = {Pietro Benedusi and Carlo Garoni and Rolf Krause and
Xiaozhou Li and Stefano Serra-Capizzano},
title = {Discontinuous {G}alerkin Discretization of the Heat
Equation in Any Dimension: the Spectral Symbol},
institution = it,
department = tdb,
year = 2018,
number = {2018-002},
month = jan,
abstract = {The multidimensional heat equation, along with its more
general version involving variable diffusion coefficients,
is discretized by a discontinuous Galerkin (DG) method in
time and a finite element (FE) method of arbitrary
regularity in space. We show that the resulting space-time
discretization matrices enjoy an asymptotic spectral
distribution as the mesh fineness increases, and we
determine the associated spectral symbol, i.e., the
function that carefully describes the spectral
distribution. The analysis of this paper is carried out in
a stepwise fashion, without omitting details, and it is
supported by several numerical experiments. It is
preparatory to the development of specialized solvers for
linear systems arising from the DG/FE approximation of the
heat equation in the case of both constant and variable
diffusion coefficients.}
}
@TechReport{ it:2018-001,
author = {Carlo Garoni and Stefano Serra-Capizzano and Debora
Sesana},
title = {The Theory of Block Generalized Locally Toeplitz
Sequences},
institution = it,
department = tdb,
year = 2018,
number = {2018-001},
month = jan,
note = {Updated 2018-01-30.},
abstract = {The theory of generalized locally Toeplitz (GLT) sequences
is a powerful apparatus for computing the asymptotic
singular value and eigenvalue distribution of matrices
$A_n$ arising from virtually any kind of numerical
discretization of differential equations (DEs). Indeed,
when the discretization parameter $n$ tends to infinity,
these matrices $A_n$ give rise to a sequence $\{A_n\}_n$,
which often turns out to be a GLT sequence or one of its
`relatives', i.e., a block GLT sequence or a reduced GLT
sequence. In particular, block GLT sequences are
encountered in the discretization of systems of DEs as well
as in the higher-order finite element or discontinuous
Galerkin approximation of scalar DEs. Despite the
applicative importance, a solid theory of block GLT
sequences is still missing. The purpose of the present
paper is to develop this theory in a systematic way.}
}
@TechReport{ it:2017-024,
title = {Coupled Electric Drives Data Set and Reference Models},
author = {Torbj{\"o}rn Wigren and Maarten Schoukens},
institution = it,
department = syscon,
year = 2017,
number = {2017-024},
month = nov,
note = {The data set can be downloaded from
\url{http://www.it.uu.se/research/publications/reports/2017-024/CoupledElectricDrivesDataSetAndReferenceModels.zip}.}
,
abstract = {The following report provides a description of the CE8
coupled electric drives laboratory process. A first set of
continuous time model structures that are suitable to
describe the nonlinear dynamics are presented. The data
sets, which are available in .mat and .csv file formats,
are then described in detail. The available data sets are
short, which constitute a challenge when performing
identification. In support of future work, Wiener models
are identified with a recursive algorithm that is
parameterized in continuous time. This approach reduces the
number of parameters to four for identification of third
order dynamics.}
}
@TechReport{ it:2017-023,
author = {Kim-Anh Tran and Alexandra Jimborean and Trevor E. Carlson
and Magnus Sj{\"a}lander and Konstantinos Koukos and
Stefanos Kaxiras},
title = {Transcending Hardware Limits with Software Out-Of-Order
Execution},
institution = it,
department = docs,
year = 2017,
number = {2017-023},
month = oct,
abstract = {Reducing the widening gap between processor and memory
speed has been steering processors' design over the last
decade, as memory accesses became the main performance
bottleneck. Out-of-order architectures attempt to hide
memory latency by dynamically reordering instructions,
while in-order architectures are restricted to static
instruction schedules. We propose a software-hardware
co-design to break out of the hardware limits of existing
architectures and attain increased memory and instruction
level parallelism by orchestrating coarse-grain
out-of-program-order execution in software (SWOOP). On
in-order architectures, SWOOP acts as a virtual reorder
buffer (ROB) while out-of-order architectures are endowed
with the ability to jump ahead to independent code, far
beyond the reach of the ROB. We build upon the decoupled
access-execute model, however, executed in a single
superscalar pipeline and within a single thread of control.
The compiler generates the Access and Execute code slices
and orchestrates their execution out-of-order, with the
support of frugal microarchitectural enhancements to
maximize efficiency. SWOOP significantly improves the
performance of memory-bound applications by 42\% on
in-order cores, and by 43\% on out-of-order architectures.
Furthermore, not only is SWOOP competitive with
out-of-order cores which benefit from double-sized reorder
buffers, but it is also considerably more energy efficient.
}
}
@TechReport{ it:2017-022,
author = {Ali Dorostkar},
title = {Function-Based Algebraic Multigrid Method for the {3D}
{P}oisson Problem on Structured Meshes},
institution = it,
department = tdb,
year = 2017,
number = {2017-022},
month = oct,
abstract = {Multilevel methods, such as Geometric and Algebraic
Multigrid, Algebraic Multilevel Iteration, Domain
Decomposition-type methods have been shown to be the
methods of choice for solving linear systems of equations,
arising in many areas of Scientific Computing. The methods,
in particular the multigrid methods, have been efficiently
implemented in serial and parallel and are available via
many scientific libraries.
The multigrid methods are primarily used as preconditioners
for various Krylov subspace iteration methods. They exhibit
convergence that is independent or nearly independent on
the number of degrees of freedom and can be tuned to be
also robust with respect to other problem parameters. The
methods also possess optimal computational complexity. As a
drawback, of particular importance when solving very large
scale problems, we point out their high demand for computer
memory. Since the methods utilize hierarchical structures,
where the amount of computations decreases and that of
communication increases, their parallel implementation
might exhibit lesser scalability. Further, as the
implementation usually relies on sparse matrix-vector
multiplications, this may also decrease parallel
performance for very large problems.
In this work we utilize a different framework to construct
multigrid methods, based on an analytical function
representation of the matrix, that may keep the amount of
computation high and local and may reduce significantly the
memory requirements. The approach is particularly suitable
for modern computer architectures. An implementation of the
latter for the three-dimensional discrete Laplace operator
is derived and implemented. The same function
representation technology is used to construct smoothers of
approximate inverse type.},
note = {Updated 2017-10-26.}
}
@TechReport{ it:2017-021,
author = {Umberto Soverini and Torsten S{\"o}derstr{\"o}m},
title = {Identification of Two Dimensional Complex Sinusoids in
White Noise: a State-Space Frequency Approach},
institution = it,
department = syscon,
year = 2017,
number = {2017-021},
month = oct,
note = {Updated by Technical Report 2018-007, April 2018. See
\url{http://www.it.uu.se/research/publications/reports/2018-007}.}
,
abstract = {This paper proposes a new frequency domain approach for
identifying the parameters of two–dimensional complex
sinusoids from a finite number of data, when the
measurements are affected by additive and uncorrelated
two–dimensional white noise. The new method extends in
two dimensions a frequency identification procedure of
complex sinusoids, originally developed for the
one–dimensional case. The properties of the proposed
method are analyzed by means of Monte Carlo simulations and
its features are compared with those of other estimation
algorithms. In particular the practical advantage of the
method will be highlighted. In fact the novel approach can
operate just on a specified sub–area of the 2D spectrum.
This area–selective feature allows a drastic reduction of
the computational complexity, which is usually very high
when standard time domain methods are used.}
}
@TechReport{ it:2017-020,
author = {Umberto Soverini and Torsten S{\"o}derstr{\"o}m},
title = {2D-Frequency Domain Identification of Complex Sinusoids in
the Presence of Additive Noise},
institution = it,
department = syscon,
year = 2017,
number = {2017-020},
month = oct,
note = {Updated by Technical Report 2018-006, April 2018. See
\url{http://www.it.uu.se/research/publications/reports/2018-006}.}
,
abstract = {This paper describes a new approach for identifying the
parameters of two–dimensional complex sinusoids from a
finite number of measurements, in presence of additive and
uncorrelated two–dimensional white noise. The proposed
approach is based on using frequency domain data. As a
major feature, it enables the estimation to be frequency
selective. The new method extends to the two–dimensional
(2D) case some recent results obtained with reference to
the frequency ESPRIT algorithm. The properties of the
proposed method are analyzed by means of Monte Carlo
simulations and its features are compared with those of a
classical time domain estimation algorithm. The practical
advantages of the method are highlighted. In fact the novel
approach can operate just on a specified sub–area of the
2D spectrum. This area–selective feature allows a drastic
reduction of the computational complexity, which is usually
very high when standard time domain methods are used.}
}
@TechReport{ it:2017-019,
author = {Zhouyang Ge and Hanna Holmgren and Martin Kronbichler and
Luca Brandt and Gunilla Kreiss},
title = {Effective Slip Over Partially Filled Microcavities and its
Possible Failure},
institution = it,
department = tdb,
year = 2017,
number = {2017-019},
month = sep,
abstract = {Microscale roughness on an otherwise smooth hydrophobic
surface can significantly reduce the resistance to an
external liquid flow. We study static drag reduction over a
lubricant- infused surface by looking at an array of
two-dimensional transverse grooves partially filled with a
second immiscible fluid. Numerical simulations at separate
length scales are used to probe the static drag reduction
property and the dynamic wetting behavior. Nano-scale phase
field simulations are used to extract the characteristic
contact line velocities. Micron-scale two-phase simulations
using the level set method are used to model the interface
deformation and the flow in and above the cavities. We
study the dependence of the effective slip by varying
viscosity ratios, capillary numbers, the static contact
angle and the filling rate of the cavity (meaning the
amount of lubricant fluid). We observe an increase of the
effective slip with the cavity filling and identify a
potentially new failure mode.}
}
@TechReport{ it:2017-018,
author = {Antonio Cicone and Carlo Garoni and Stefano
Serra-Capizzano},
title = {Spectral and Convergence Analysis of the Discrete {ALIF}
Method},
institution = it,
department = tdb,
year = 2017,
number = {2017-018},
month = sep,
abstract = {The Adaptive Local Iterative Filtering (ALIF) method is a
recently proposed iterative procedure to decompose a signal
into a finite number of ``simple components'' called
intrinsic mode functions. % It is an alternative to the
well-known and widely used empirical mode decomposition, a
method proposed in 1998 by Huang and his research team at
NASA. % In this paper we consider the discrete version of
the ALIF method and we perform a spectral analysis of the
related iteration matrices, with particular focus on the
eigenvalue clustering and the eigenvalue distribution. %
Based on the eigenvalue distribution, we formulate a
necessary condition for the convergence of the Discrete
ALIF method. We also provide a simple criterion to
construct appropriate filters satisfying this condition. %
Our analysis, which represents a first step toward a
complete mathematical understanding of the ALIF method,
relies on recent matrix-theoretic results about sampling
matrices and, above all, on the theory of generalized
locally Toeplitz sequences, which we extend in this paper.
% Several numerical examples in support of the theoretical
analysis are presented.}
}
@TechReport{ it:2017-017,
author = {Owe Axelsson and Zhao-Zheng Liang and Maya Neytcheva},
title = {Parallel Solution Methods and Preconditioners for
Evolution Equations},
institution = it,
department = tdb,
year = 2017,
number = {2017-017},
month = sep,
abstract = {The recent development of the high performance computer
platforms shows a clear trend towards heterogeneity and
hierarchy. In order to utilize the computational power
particular attention must be paid to finding new algorithms
or adjust existing ones so that they better match the HPC
computer architecture.
In this work we consider an alternative to classical
time-stepping methods based on use of time-harmonic
properties and discuss solution approaches that allow
efficient utilization of modern HPC resources. The method
in focus is based on a truncated Fourier expansion of the
solution of an evolutionary problem. The analysis is done
for linear equations and it is remarked on the possibility
to use two- or multilevel methods for nonlinear problems,
which can add to an even higher degree of parallelization.
The arising block matrix system to be solved admits a
two-by-two block form with square blocks, for which a very
efficient preconditioner exists. It leads to tight
eigenvalue bounds for the preconditioned matrix and, hence,
to a very fast convergence of a preconditioned Krylov
subspace or iterative refinement method. The analytical
background is shown as well as some illustrating numerical
examples. }
}
@TechReport{ it:2017-016,
author = {Sven-Erik Ekstr{\"o}m and Isabella Furci and Stefano
Serra-Capizzano},
title = {Are the Eigenvalues of the B-spline IgA Approximation of
$-\Delta u = \lambda u$ Known in Almost Closed Form?},
institution = it,
department = tdb,
year = 2017,
number = {2017-016},
month = aug,
abstract = {In this paper we consider the B-spline IgA approximation
of the second-order eigenvalue problem $-\Delta u = \lambda
u$ on $\Omega=(0,1)^d$, with zero Dirichlet boundary
conditions and with $\Delta = \sum_{j=1}^{d}
\frac{\partial^2}{\partial x_j^2}$, $d\ge 1$. We use
B-splines of degree ${\bf p}=(p_1,\ldots,p_d)$ and maximal
smoothness and we consider the natural Galerkin approach.
By using elementary tensor arguments, we show that the
eigenvalue-eigenvector structure of the discrete problem
can be reduced to the case of $d=1, p\ge 1$, regularity
$C^{p-1}$, with coefficient matrix $L_n^{[p]}$ having size
$N(n,p)=n+p-2$. In previous works, it has been established
that the normalized sequence $\{n^{-2}L_n^{[p]}\}_n$ has a
canonical distribution in the eigenvalue sense and the
so-called spectral symbol $e_p(\theta)$ has been identified.
In this paper we provide numerical evidence of a precise
asymptotic expansion for the eigenvalues, which obviously
begins with the function $e_p$, up to the largest $n_p^{\rm
out}=p+{\rm mod}(p,2)-2$ eigenvalues which behave as
outliers. More precisely, for every integer $\alpha\ge0$,
every $n$, every $p\ge 3$ and every $j=1,\ldots,\hat
N=N(n,p)-n_p^{\rm out}=n-{\rm mod}(p,2)$, the following
asymptotic expansion holds: \begin{align*} \lambda_j(n^{-2}
L_n^{[p]})=e_p(\theta_{j,n,p})+\sum_{k=1}^{\alpha}c_k^{(p)}(\theta_{j,n,p})h^k+E_{j,n,\alpha}^{(p)},
\end{align*} where: \begin{itemize} \item the eigenvalues
of $n^{-2}L_n^{[p]}$ are arranged in nondecreasing order
and $e_p$ is increasing; \item
$\{c_k^{(p)}\}_{k=1,2,\ldots}$ is a sequence of functions
from $[0,\pi]$ to $\mathbb R$ which depends only on $e_p$;
\item for any $p\ge 3$ and $k$, there exists
$\bar\theta(p,k)>0$ such that $c_k^{(p)}$ vanishes (at
least numerically) on the whole nontrivial interval
$[0,\bar\theta(p,k)]$, so that the formula is exact, up to
machine precision, for a large portion of the small
eigenvalues; \item $h=\frac{1}{n}$ and
$\theta_{j,n,p}=\frac{j\pi}{n}=j\pi h$, $j=1,\ldots, n-{\rm
mod}(p,2)$; \item $E_{j,n,\alpha}^{(p)}=O(h^{\alpha+1})$ is
the remainder (the error), which satisfies the inequality
$|E_{j,n,\alpha}^{(p)}|\le C_{\alpha} h^{\alpha+1}$ for
some constant $C_{\alpha}$ depending only on $\alpha$ and
$e_p$. \end{itemize} For the case $p=1,2$ the complete
structure of the eigenvalues and eigenvectors is identified
exactly. Indeed, for such values of $p$, the matrices
$L_n^{[p]}$ belong to Toeplitz -minus- Hankel algebras and
this is also the reason why there are no outliers, that is
$n_p^{\rm out}=0$.
Moreover, for $p\ge 3$ and based on the eigenvalue
asymptotics for $n^{-2}L_n^{[p]}$, we devise an
extrapolation algorithm for computing the eigenvalues of
the discrete problem with a high level of accuracy and with
a relatively negligible computational cost. However, the
algorithm is not necessary for all the spectrum and indeed,
for $p\ge 3$ and $\theta_{j,n,p}$ belonging to the interval
$[0,\bar\theta(p)]$, $\bar\theta(p)=\inf_k
\bar\theta(p,k)$, the value $e_p(\theta_{j,n,p})$ coincides
with $\lambda_j(n^{-2} L_n^{[p]})$, up to machine precision.
Such expansions are of the same type studied in the
literature for the eigenvalues of a sequence of Toeplitz
matrices $\{T_n(f)\}$ and of a sequence of preconditioned
Toeplitz matrices $\{T_n^{-1}(g)T_n(f)\}$, for $f$
trigonometric polynomial, $g$ nonnegative, not identically
zero trigonometric polynomial.
Extensive numerical experiments are discussed and further future research steps are illustrated at the end of the paper. }
}
@TechReport{ it:2017-015,
author = {Sven-Erik Ekstr{\"o}m and Carlo Garoni},
title = {An Interpolation-Extrapolation Algorithm for Computing the
Eigenvalues of Preconditioned Banded Symmetric Toeplitz
Matrices},
institution = it,
department = tdb,
year = 2017,
number = {2017-015},
month = aug,
abstract = {In the past few years, Bogoya, B{\"o}ttcher, Grudsky, and
Maximenko obtained for the eigenvalues of a Toeplitz matrix
$T_n(f)$, under suitable assumptions on the generating
function $f$, the precise asymptotic expansion as the
matrix size $n$ goes to infinity. On the basis of several
numerical experiments, it was conjectured by
Serra-Capizzano that a completely analogous expansion also
holds for the eigenvalues of the preconditioned Toeplitz
matrix $T_n(u)^{-1}T_n(v)$, provided $f=v/u$ is monotone
and further conditions on $u$ and $v$ are satisfied. Based
on this expansion, we here propose and analyze an
interpolation--extrapolation algorithm for computing the
eigenvalues of $T_n(u)^{-1}T_n(v)$. We illustrate the
performance of the algorithm through numerical experiments
and we also present its generalization to the case where
$f=v/u$ is non-monotone.}
}
@TechReport{ it:2017-014,
author = {Zhao-Zheng Liang and Owe Axelsson and Maya Neytcheva},
title = {A Robust Structured Preconditioner for Time-Harmonic
Parabolic Optimal Control Problems},
institution = it,
department = tdb,
year = 2017,
number = {2017-014},
month = aug,
abstract = {We consider the iterative solution of optimal control
problems constrained by the time-harmonic parabolic
equations. Due to the time-harmonic property of the control
equations, a suitable discretization of the corresponding
optimality systems leads to a large complex linear system
with special two-by-two block matrix of saddle point form.
For this algebraic system, an efficient preconditioner is
constructed, which results in a fast Krylov subspace
solver, that is robust with respect to the mesh size,
frequency and regularization parameters. Furthermore, the
implementation is straightforward and the computational
complexity is of optimal order, linear in the number of
degrees of freedom. We show that the eigenvalue
distribution of the corresponding preconditioned matrix
leads to a condition number bounded above by 2. Numerical
experiments confirming the theoretical derivations are
presented, including comparisons with some other existing
preconditioners.}
}
@TechReport{ it:2017-013,
author = {Davide Bianchi and Stefano Serra-Capizzano},
title = {Spectral Analysis of Finite-Difference Approximations of
$1-d$ Waves in Non-Uniform Grids},
institution = it,
department = tdb,
year = 2017,
number = {2017-013},
month = jul,
abstract = {Preserving the finite positive velocity of propagation of
continuous solutions of wave equations is one of the key
issues, when building numerical approximation schemes for
control and inverse problems. And this is hard to achieve
uniformly on all possible ranges of numerical solutions. In
particular, high frequencies often generate spurious
numerical solutions, behaving in a pathological manner and
making the propagation properties of continuous solutions
fail. The latter may lead to the divergence of the ``most
natural" approximation procedures for numerical control or
identification problems.
On the other hand, the velocity of propagation of high
frequency numerical wave-packets, the so-called group
velocity, is well known to be related to the spectral gap
of the corresponding discrete spectra. Furthermore most
numerical schemes in uniform meshes fail to preserve the
uniform gap property and, consequently, do not share the
propagation properties of continuous waves.
However, recently, S. Ervedoza, A. Marica and the E. Zuazua
have shown that, in $1-d$, uniform propagation properties
are ensured for finite-difference schemes in suitable
non-uniform meshes behaving in a monotonic manner. The
monotonicity of the mesh induces a preferred direction of
propagation for the numerical waves. In this way, meshes
that are suitably designed can ensure that all numerical
waves reach the boundary in an uniform time, which is the
key for the fulfillment of boundary controllability
properties.
In this paper we study the gap of discrete spectra of the
Laplace operator in $1-d$ for non-uniform meshes, analysing
the corresponding spectral symbol, which allows to show how
to design the discretization grid for improving the gap
behaviour. The main tool is the study of an univariate
monotonic version of the spectral symbol, obtained by
employing a proper rearrangement.
The analytical results are illustrated by a number of
numerical experiments. We conclude discussing some open
problems.}
}
@TechReport{ it:2017-012,
author = {Fayyaz Ahmad and Eman Salem Al-Aidarous and Dina Abdullah
Alrehaili and Sven-Erik Ekstr{\"o}m and Isabella Furci and
Stefano Serra-Capizzano},
title = {Are the Eigenvalues of Preconditioned Banded Symmetric
{T}oeplitz Matrices Known in Almost Closed Form?},
institution = it,
department = tdb,
year = 2017,
number = {2017-012},
month = jun,
abstract = {Bogoya, B{\"o}ttcher, Grudsky, and Maximenko have recently
obtained the precise asymptotic expansion for the
eigenvalues of a sequence of Toeplitz matrices
$\{T_n(f)\}$, under suitable assumptions on the associated
generating function $f$. In this paper we provide numerical
evidence that some of these assumptions can be relaxed and
extended to the case of a sequence of preconditioned
Toeplitz matrices $\{T_n^{-1}(g)T_n(f)\}$, for $f$
trigonometric polynomial, $g$ nonnegative, not identically
zero trigonometric polynomial, $r=f/g$, and where the ratio
$r(\cdot)$ plays the same role as $f(\cdot)$ in the
nonpreconditioned case. Moreover, based on the eigenvalue
asymptotics, we devise an extrapolation algorithm for
computing the eigenvalues of preconditioned banded
symmetric Toeplitz matrices with a high level of accuracy,
with a relatively low computational cost, and with
potential application to the computation of the spectrum of
differential operators.}
}
@TechReport{ it:2017-011,
author = {Sholeh Yasini and Torbj{\"o}rn Wigren},
title = {Parametric Convergence Analysis of an Adaptive Filtering
Algorithm with Output Quantization},
institution = it,
department = tdb,
year = 2017,
number = {2017-011},
month = jun,
abstract = {This report analyses global parametric convergence
properties of a recursive algorithm for identification of
linear finite impulse response (FIR) dynamics with
quantized output measurements. The problem is addressed by
analytic calculation of the right hand side of the
associated ODE for a second order model. The ODE is then
analysed numerically to investigate the possibilities for
proving parametric convergence based on the coupling
between the switch point and the dynamic gain.}
}
@TechReport{ it:2017-010,
author = {Sven-Erik Ekstr{\"o}m and Stefano Serra-Capizzano},
title = {Eigenvalues and Eigenvectors of Banded {T}oeplitz Matrices
and the Related Symbols},
institution = it,
department = tdb,
year = 2017,
number = {2017-010},
month = may,
abstract = {It is known that for the tridiagonal Toeplitz matrix,
having the main diagonal with constant $a_0=2$ and the two
first off-diagonals with constants $a_{1}=-1$ (lower) and
$a_{-1}=-1$ (upper), there exists closed form formulas,
giving the eigenvalues of the matrix and a set of
associated eigenvectors. The latter matrix corresponds to
the well known case of the 1D discrete Laplacian, but with
a little care the formulas can be generalized to any triple
$(a_0,a_{1},a_{-1})$ of complex values.
In the first part of this article, we consider a
tridiagonal Toeplitz matrix of the same form
$(a_0,a_{\omega},a_{-\omega})$, but where the two
off-diagonals are positioned $\omega$ steps from the main
diagonal instead of only one. We show that its eigenvalues
and eigenvectors also can be identified in closed form. To
achieve this, ad hoc sampling grids have to be considered,
in connection with a new symbol associated with the
standard Toeplitz generating function. In the second part,
we restrict our attention to the symmetric real case
($a_0,a_{\omega}=a_{-\omega}$ real values) and we analyze
the relations with the standard generating function of the
Toeplitz matrix. Furthermore, as numerical evidences
clearly suggest, it turns out that the eigenvalue behavior
of a general banded symmetric Toeplitz matrix with real
entries can be described qualitatively in terms of that of
the symmetrically sparse tridiagonal case with real $a_0$,
$a_{\omega}=a_{-\omega}$, $\omega=2,3,\ldots$, and also
quantitatively in terms of that having monotone symbols, as
those related to classical Finite Difference discretization
of the operators $(-1)^q \frac{\partial^{2q}}{\partial
x^{2q}}$, where the case of $q=1$ coincides with $a_0=2$,
$a_{1}=a_{-1}=-1$.}
}
@TechReport{ it:2017-009,
author = {Mariarosa Mazza and Ahmed Ratnani and Stefano
Serra-Capizzano},
title = {Spectral Analysis and Spectral Symbol for the {2D}
curl-curl (Stabilized) Operator with Applications to the
Related Iterative Solutions},
institution = it,
department = tdb,
year = 2017,
number = {2017-009},
month = apr,
abstract = {In this paper, we study structural and spectral features
of linear systems of equations arising from Galerkin
approximations of $H(\mathrm{curl})$ elliptic variational
problems, based on the Isogeometric Analysis (IgA)
approach. Such problems arise in Time Harmonic Maxwell and
magnetostatic problems, as well in the preconditioning of
MagnetoHydroDynamics equations, and lead to large linear
systems, with different and severe sources of
ill-conditioning.
First, we consider a Compatible B-Splines discretization
based on a discrete De Rham sequence and we study the
structure of the resulting matrices $\mathcal{A}_{n}$. It
turns out that $\mathcal{A}_{n}$ shows a two-by-two pattern
and is a principal submatrix of a two-by-two block matrix,
where each block is two-level banded, almost Toeplitz, and
where the bandwidths grow linearly with the degree of the
B-splines.
Looking at the coefficients in detail and making use of the
theory of the Generalized Locally Toeplitz (GLT) sequences,
we identify the symbol of each of these blocks, that is a
function describing asymptotically, i.e., for $n$ large
enough, the spectrum of each block. From this spectral
knowledge and thanks to some new spectral tools we retrieve
the symbol of $\{\mathcal{A}_{n}\}_{n}$ which as expected
is a two-by-two matrix-valued bivariate trigonometric
polynomial. In particular, there is a nice elegant
connection with the continuous operator, which has an
infinite dimensional kernel, and in fact the symbol is a
dyad having one eigenvalue like the one of the IgA
Laplacian, and one identically zero eigenvalue: as a
consequence, we prove that one half of the spectrum of
$\mathcal{A}_{n}$, for $\nn$ large enough, is very close to
zero and this represents the discrete counterpart of the
infinite dimensional kernel of the continuous operator.
From the latter information, we are able to give a detailed
spectral analysis of the matrices $\mathcal{A}_{n}$, which
is fully confirmed by several numerical evidences.
Finally, by taking into consideration the GLT theory and
making use of the spectral results, we furnish indications
on the convergence features of known iterative solvers and
we suggest proper iterative techniques for the numerical
solution of the involved linear systems.}
}
@TechReport{ it:2017-008,
author = {Mahdad Davari and Erik Hagersten and Stefanos Kaxiras},
title = {Scope-Aware Classification: Taking the Hierarchical
Private/Shared Data Classification to the Next Level},
institution = it,
department = docs,
year = 2017,
number = {2017-008},
month = apr,
abstract = {Hierarchical techniques are commonplace in ameliorating
the bottlenecks, such as cache coherence, in the design of
scalable multi/manycores. Furthermore, there have been
proposals to simplify the coherence based on the
data-race-free semantics of the software and private/shared
data classification, where cores self-invalidate their
shared data upon synchronizations. However, naive
private/shared data classification in the hierarchies
nullifies such optimizations by increasing the amount of
data misclassified as shared and therefore being needlessly
self-invalidated.
We introduce a private/shared data classification approach
for hierarchical clusters, where a datum is concurrently
classified as private and shared with respect to different
classification scopes. Such scope-aware classification
eliminates the needless self-invalidation of the valid data
at synchronizations, resulting in a coherence scheme that
reduces the average network traffic and execution time by
30\% and 5\%, respectively. }
}
@TechReport{ it:2017-007,
author = {Torbj{\"o}rn Wigren},
title = {{MATLAB} Software for Nonlinear and Delayed Recursive
Identification - Revision 1},
institution = it,
department = tdb,
year = 2017,
number = {2017-007},
month = apr,
note = {The software package can be downloaded from
\url{http://www.it.uu.se/research/publications/reports/2017-007/RecursiveNonlinearNetworkedIdentificationSW.zip}.}
,
abstract = {This report is the user~s manual for a package of MATLAB
scripts and functions, developed for recursive prediction
error identification of nonlinear state space systems. The
identified state space model incorporates delay, which
allows a treatment of general nonlinear networked
identification, as well as of general nonlinear systems
with delay. The core of the package is an implementation of
an output error identification algorithm. The algorithm is
based on a continuous time, structured black box state
space model of a nonlinear system. The software can only be
run off-line, i.e. no true real time operation is possible.
The algorithms are however implemented so that true on-line
operation can be obtained by extraction of the main
algorithmic loop. The user must then provide the real time
environment. The software package contains scripts and
functions that allow the user to either input live
measurements or to generate test data by simulation. The
scripts and functions for the setup and execution of the
identification algorithms are somewhat more general than
what is described in the references. The functionality for
display of results include scripts for plotting of e.g.
data, parameters, prediction errors, eigenvalues and the
condition number of the Hessian. The estimated model
obtained at the end of a run can be simulated and the model
output plotted, alone or together with the data used for
identification. Model validation is supported by two
methods apart from the display functionality. First, a
calculation of the RPEM loss function can be performed,
using parameters obtained at the end of an identification
run. Secondly, the accuracy as a function of the output
signal amplitude can be assessed.}
}
@TechReport{ it:2017-006,
author = {Karl Ljungkvist and Martin Kronbichler},
title = {Multigrid for Matrix-Free Finite Element Computations on
Graphics Processors},
institution = it,
department = tdb,
year = 2017,
number = {2017-006},
month = apr,
note = {Updated 2017-04-20.},
abstract = {In this paper, we consider matrix-free finite-element
techniques for efficient numerical solution of partial
differential equations on modern manycore processors such
as graphics cards. We present a GPU parallelization of a
completely matrix-free geometric multigrid iterative
solver, with support for general curved and adaptively
refined meshes with hanging nodes. Comparing our
implementation running on a Pascal P100 GPU to a highly
optimized multi-core implementation running on comparable
Broadwell CPUs, we demonstrate speedups of around a factor
of 2x across three different Poisson-based applications and
a variety of element degrees in 2D and 3D. We also show
that atomic intrinsics is consistently the fastest way for
shared-memory updates on the GPU, in contrast to previous
architectures, and mixed-precision arithmetic can be used
successfully, yielding a speedup of up to 83\% over a full
double precision approach.}
}
@TechReport{ it:2017-005,
author = {Saleh Rezaeiravesh and Mattias Liefvendahl},
title = {Grid Construction Strategies for Wall-Resolving Large Eddy
Simulation and Estimates of the Resulting Number of Grid
Points},
institution = it,
department = tdb,
year = 2017,
number = {2017-005},
month = apr,
abstract = {Estimates of the total number of grid points required for
wall-resolving large eddy simulation (WR-LES) of canonical
wall-bounded turbulent flows, corresponding to different
grid construction strategies, are derived. The common basis
for all strategies is that the first off-wall grid spacing
is of the order of the local viscous length scale. First,
the estimate of the number of grid points for the
block-nested grids, which are widely used in literature to
calculate the computational cost of WR-LES, is reviewed in
a general setting. Then, different functions, with
appropriate controlling parameters, are introduced for
distributing the grid points in the wall-normal direction.
By using these functions along with assuming grid spacings
in the streamwise and spanwise directions to be independent
of the wall-normal coordinate, block-structured grids can
be constructed, for which analytical expressions are
derived to show the dependency of the total number of grid
points to the flow Reynolds number. It is shown that under
equivalent conditions, this class of grids demands more
grid points than the block-nested ones. In particular, for
a zero-pressure-gradient turbulent boundary layer at high
Reynolds numbers, the increase in the number of grid points
can be up to $\mathcal{O}(10^2)$, which relaxes to up to
$\mathcal{O}(10)$ for fully-developed turbulent channel
flow.}
}
@TechReport{ it:2017-004,
author = {Owe Axelsson and Maya Neytcheva and Anders Str{\"o}m},
title = {An Efficient Preconditioning Method for State
Box-Constrained Optimal Control Problems},
institution = it,
department = tdb,
year = 2017,
number = {2017-004},
month = mar,
note = {Updated 2017-04-12. A major revision appears in Technical
Report 2018-008, see
\url{http://www.it.uu.se/research/publications/reports/2018-008}.}
,
abstract = {An efficient preconditioning technique used earlier for
two-by-two block matrix systems with square matrices is
shown to be applicable also for a state variable
box-constrained optimal control problem. The problem is
penalized by a standard regularization term for the control
variable and for the box-constraint, using a Moreau-Yosida
penalization method. It is shown that there arises very few
nonlinear iteration steps and also few iterations to solve
the arising linearized equations on the fine mesh. This
holds for a wide range of the penalization and
discretization parameters. The arising nonlinearity can be
handled with a hybrid nonlinear-linear procedure that
raises the computational efficiency of the overall solution
method.}
}
@TechReport{ it:2017-003,
author = {Pavol Bauer and Stefan Engblom},
title = {The {URDME} manual Version 1.3},
institution = it,
department = tdb,
year = 2017,
number = {2017-003},
month = mar,
abstract = {We have developed URDME, a general software for simulation
of stochastic reaction-diffusion processes on unstructured
meshes. This allows for a more flexible handling of
complicated geometries and curved boundaries compared to
simulations on structured, cartesian meshes. The underlying
algorithm is the next subvolume method, extended to
unstructured meshes by obtaining jump coefficients from a
finite element formulation of the corresponding macroscopic
equation.
This manual describes version 1.3 of the software. URDME
1.3 includes support for Comsol Multiphysics 5.x and PDE
Toolbox version 1.5 and above.}
}
@TechReport{ it:2017-002,
author = {C. Garoni and S. Serra-Capizzano},
title = {{G}eneralized {L}ocally {T}oeplitz Sequences: Theory and
Applications},
institution = it,
department = tdb,
year = 2017,
number = {2017-002},
month = feb,
abstract = {We present an extensive review on the theory of
Generalized Locally Toeplitz (GLT) matrix-sequences, as an
extension of the theory of Toeplitz operators and of the
Fourier Analysis for variable-coefficients
integrodifferential operators.}
}
@TechReport{ it:2017-001,
author = {Mattias Liefvendahl and Timofey Mukha and Saleh
Rezaeiravesh},
title = {Formulation of a Wall Model for {LES} in a Collocated
Finite-Volume Framework},
institution = it,
department = tdb,
year = 2017,
number = {2017-001},
month = jan,
abstract = {Wall-modelled Large-Eddy Simulation (WMLES) is a
turbulence modelling approach that aims to reduce the
computational costs of traditional (wall-resolved) LES by
introducing special treatment of the near-wall region. In
this report, a detailed derivation is given of a widely
used wall model which is based on implicitly enforcing the
correct local wall shear stress. The model is developed in
the framework of a collocated finite volume method, with
unstructured meshes and arbitrary polyhedral grid cells.
The expression for the law of the wall proposed by Spalding
is used to relate the finite volume cell flow velocity to
the wall-shear stress. The computational cost and
predictive accuracy of the overall method is evaluated by a
series of turbulent channel flow simulations covering a
range of Re-numbers, from $10\,000$ to $125\,000$, based on
the bulk velocity and channel half-height. For validation,
the WMLES-results are compared to publicly available
results from direct numerical simulations. It is
demonstrated that the WMLES approach significantly reduces
the computational cost, as compared to wall-resolved LES,
while maintaining an acceptable accuracy of, at least,
first-order statistical moments of the unknowns.}
}
@TechReport{ it:2016-017,
author = {S.-E. Ekstr{\"o}m and S. Serra-Capizzano},
title = {Eigenvalues of Banded Symmetric {T}oeplitz Matrices are
Known Almost in Close Form?},
institution = it,
department = tdb,
year = 2016,
number = {2016-017},
month = sep,
abstract = {It is well-known that the eigenvalues of (real) symmetric
banded Toeplitz matrices of size $n$ are approximately
given by an equispaced sampling of the symbol $f(\theta)$,
up to an error which grows at most as $h=(n+1)^{-1}$, where
the symbol is a real-valued cosine polynomial.
Under the condition that $f$ is monotone, we show that
there is hierarchy of symbols so that
\[ \lambda_{j}^{(h)}-f\left(\theta_{j}^{(h)}\right)=\sum_k
c_k\left(\theta_{j}^{(h)}\right)\, h^k,\quad \quad
\theta_j^{(h)}=j\pi h, j=1,\ldots,n, \]
with $c_k(\theta)$ higher order symbols. In the general
case, a more complicate expression holds but still we find
a structural hierarchy of symbols. The latter asymptotic
expansions constitute a starting point for computing the
eigenvalues of large symmetric banded Toeplitz matrices by
using classical extrapolation methods.
Selected numerics are shown in 1D and a similar study is
briefly discussed in the multilevel setting ($d$D, $d\ge
2$) with blocks included, so opening the door to a fast
computation of the spectrum of matrices approximating
partial differential operators.}
}
@TechReport{ it:2016-016,
author = {Torsten S{\"o}derstr{\"o}m and Umberto Soverini},
title = {Errors-in-Variables Identification using Maximum
Likelihood Estimation in the Frequency Domain},
institution = it,
department = syscon,
year = 2016,
number = {2016-016},
month = sep,
abstract = {This report deals with the identification of
errors-in-variables (EIV) models corrupted by additive and
uncorrelated white Gaussian noises when the noise--free
input is an arbitrary signal, not required to be periodic.
In particular, a frequency domain maximum likelihood (ML)
estimator is proposed and analyzed in some detail. As some
other EIV estimators, this method assumes that the ratio of
the noise variances is known. The estimation problem is
formulated in the frequency domain. It is shown that the
parameter estimates are consistent. An explicit algorithm
for computing the asymptotic covariance matrix of the
parameter estimates is derived. The possibility to
effectively use lowpass filtered data by using only part of
the frequency domain is discussed, analyzed and
illustrated. }
}
@TechReport{ it:2016-015,
author = {Afshin Zafari and Elisabeth Larsson and Marco Righero and
M. Alessandro Francavilla and Giorgio Giordanengo and
Francesca Vipiana and Giuseppe Vecchi},
title = {Task Parallel Implementation of a Solver for
Electromagnetic Scattering Problems},
institution = it,
department = tdb,
year = 2016,
number = {2016-015},
month = aug,
abstract = {Electromagnetic computations, where the wavelength is
small in relation to the geometry of interest, become
computationally demanding. In order to manage computations
for realistic problems like electromagnetic scattering from
aircraft, the use of parallel computing is essential. In
this paper, we describe how a solver based on a
hierarchical nested equivalent source approximation can be
implemented in parallel using a task based programming
model. We show that the effort for moving from the serial
implementation to a parallel implementation is modest due
to the task based programming paradigm, and that the
performance achieved on a multicore system is excellent
provided that the task size, depending on the method
parameters, is large enough.}
}
@TechReport{ it:2016-014,
author = {Vasilis Spiliopoulos and Andreas Sembrant and Georgios
Keramidas and Erik Hagersten and Stefanos Kaxiras},
title = {A Unified {DVFS}-Cache Resizing Framework},
institution = it,
department = docs,
year = 2016,
number = {2016-014},
month = aug,
abstract = {Cache resizing and DVFS are two well-known techniques,
employed to reduce leakage and dynamic power consumption
respectively. Although extensively studied, these
techniques have not been explored in combination. In this
work we argue that optimal frequency and cache size are
highly affected by each other, therefore should be studied
together.
We present a framework that drives DVFS and Cache Resizing
decisions in a unified, co-ordinated way. We show that MLP
is the key to understand how performance is affected by
both techniques and we develop an analytical model to
quantify performance variation under different cache sizes
and core frequencies. Finally, we expose this information
to the OS and/or the application, which are responsible for
setting core frequency and cache size based on
energy-efficiency policies defined by the user.
Our experimental results show that our model can drive DVFS
and Cache Resizing decisions to reduce dynamic and static
energy consumption and improve EDP by 18\% on average for
SPEC2006. We evaluate different policies and showcase that
with our model, it is trivial to build any policy involving
energy-performance requirements.}
}
@TechReport{ it:2016-013,
author = {Elias Castegren and Tobias Wrigstad},
title = {{LOLCAT}: Relaxed Linear References for Lock-free
Programming},
institution = it,
department = csd,
year = 2016,
number = {2016-013},
month = jul,
abstract = {A linear reference is a reference guaranteed to be
unaliased. This is a powerful property that simplifies
reasoning about programs, but is also a property that is
too strong for certain applications. For example, lock-free
algorithms, which implement protocols to ensure safe
concurrent access to data structures, are generally not
typable with linear references as they involve sharing of
mutable state.
This paper presents a type system with a relaxed notion of
linearity that allows an unbounded number of aliases to an
object as long as at most one alias at a time owns the
right to access the contents of the object. This ownership
can be transferred between aliases, but can never be
duplicated.
The resulting language is flexible enough to express
several lock-free algorithms and at the same time powerful
enough to guarantee the absence of data-races when
accessing owned data. The language is formalised and proven
sound, and is also available as a prototype
implementation.}
}
@TechReport{ it:2016-012,
author = {Marco Donatelli and Paola Novara and Lucia Romani and
Stefano Serra-Capizzano and Debora Sesana},
title = {Surface Subdivision Algorithms and Structured Linear
Algebra: a Computational Approach to Determine Bounds of
Extraordinary Rule Weights},
institution = it,
department = tdb,
year = 2016,
number = {2016-012},
month = jul,
abstract = {In the vicinity of extraordinary vertices, the action of a
primal subdivision scheme for the construction of arbitrary
topology surfaces can be represented by structured matrices
that form a hybrid matrix algebra related to the
block-circulant algebra. Exploiting the block
diagonalization of such matrices, we can easily take into
consideration the constraints to be satisfied by their
eigenvalues and provide an efficient computational approach
for determining the ranges of variability of the weights
defining the extraordinary rules. Application examples of
this computational strategy are shown to find the bounds of
extraordinary rule weights for improved variants of two
existing subdivision schemes.}
}
@TechReport{ it:2016-011,
author = {Ken Mattsson},
title = {Diagonal-Norm Upwind {SBP} Operators},
institution = it,
department = tdb,
year = 2016,
number = {2016-011},
month = jun,
abstract = { High-order accurate first derivative finite difference
operators are derived that naturally introduce artificial
dissipation. The boundary closures are based on the
diagonal-norm summation-by-parts (SBP) framework and the
boundary conditions are imposed using a penalty (SAT)
technique, to guarantee linear stability for a large class
of initial boundary value problems. These novel first
derivative SBP operators have a non-central difference
stencil in the interior, and come in pairs (for each order
of accuracy). The resulting SBP-SAT approximations lead to
fully explicit ODE systems. The accuracy and stability
properties are demonstrated for linear first- and
second-order hyperbolic problems in 1D, and for the
compressible Euler equations in 2D. The newly derived first
derivative SBP operators lead to significantly more robust
and accurate numerical approximations, compared with the
usage of (previously derived) central difference first
derivative SBP operators.}
}
@TechReport{ it:2016-010,
author = {Afshin Zafari and Elisabeth Larsson and Martin Tillenius},
title = {Duct{T}eip: A Task-Based Parallel Programming Framework
for Distributed Memory Architectures},
institution = it,
department = tdb,
year = 2016,
number = {2016-010},
month = jun,
abstract = {Current high-performance computer systems used for
scientific computing typically combine shared memory
compute nodes in a distributed memory environment.
Extracting high performance from these complex systems
requires tailored approaches. Task based parallel
programming has been successful both in simplifying the
programming and in exploiting the available hardware
parallelism. We have previously developed a task library
for shared memory systems which performs well compared with
other libraries. Here we extend this to distributed memory
architectures. We use a hierarchical decomposition of tasks
and data in order to accommodate the different levels of
hardware. Our experiments on implementing distributed
Cholesky factorization show that our framework has low
overhead and scales to at least 800 cores. We perform a
comparison with related frameworks and show that DuctTeip
is highly competitive in its class of frameworks. }
}
@TechReport{ it:2016-009,
author = {Andreas Svensson},
title = {On the Role of {M}onte {C}arlo Methods in {S}wedish {M.
Sc.} Engineering Education},
institution = it,
department = syscon,
year = 2016,
number = {2016-009},
month = may,
abstract = {Monte Carlo methods have quite recently become
well-established tools for scientific computations in many
different fields. We raise the question whether the
education has followed this development, and investigate to
what extent Monte Carlo methods are present in Swedish M.
Sc. engineering education today. By studying the course
syllabuses, we conclude that 11\% of the Swedish M. Sc.
engineering students are admitted to a program with a
mandatory course containing Monte Carlo methods. Further,
60\% of all students have the option to actively choose a
course which at least mentions Monte Carlo methods. Courses
containing Monte Carlo methods are mostly on advanced level
with a clear application focus, and tend to be given at the
bigger universities. We thus conclude that Monte Carlo
methods have found their way into the M. Sc. Engineering
education, but the question about level and to what extent
has perhaps not yet reached maturity among the Swedish
universities.}
}
@TechReport{ it:2016-008,
author = {Andreas Svensson and Thomas B. Sch{\"o}n},
title = {Comparing Two Recent Particle Filter Implementations of
{B}ayesian System Identification},
institution = it,
department = syscon,
year = 2016,
number = {2016-008},
month = may,
abstract = {Bayesian system identification is a theoretically
well-founded and currently emerging area. We describe and
evaluate two recent state-of-the-art sample-based methods
for Bayesian parameter inference from the statistics
literature, particle Metropolis-Hastings (PMH) and SMC$^2$,
and apply them to a non-trivial real world system
identification problem with large uncertainty present. We
discuss their different properties from a user perspective,
and conclude that they show similar performance in
practice, while PMH is significantly easier to implement
than SMC$^2$.}
}
@TechReport{ it:2016-007,
author = {Elias Castegren and Tobias Wrigstad},
title = {Reference Capabilities for Trait Based Reuse and
Concurrency Control},
institution = it,
department = csd,
year = 2016,
number = {2016-007},
month = may,
note = {Extended version of \emph{Reference Capabilities for
Concurrency Control}, ECOOP 2016..},
abstract = {The proliferation of shared mutable state in
object-oriented programming complicates software
development as two seemingly unrelated operations may
interact via an alias and produce unexpected results. In
concurrent programming this manifests itself as data-races.
Concurrent object-oriented programming further suffers from
the fact that code that warrants synchronisation cannot
easily be distinguished from code that does not. The burden
is placed solely on the programmer to reason about alias
freedom, sharing across threads and side-effects to deduce
where and when to apply concurrency control, without
inadvertently blocking parallelism.
This paper presents a reference capability approach to
concurrent and parallel object-oriented programming where
all uses of aliases are guaranteed to be data-race free.
The static type of an alias describes its possible sharing
without using explicit ownership or effect annotations.
Type information can express non-interfering deterministic
parallelism without dynamic concurrency control,
thread-locality, lock-based schemes, and guarded-by
relations giving multi-object atomicity to nested data
structures. Unification of capabilities and traits allows
trait-based reuse across multiple concurrency scenarios
with minimal code duplication. The resulting system brings
together features from a wide range of prior work in a
unified way.}
}
@TechReport{ it:2016-006,
author = {Josefin Ahlkrona},
title = {The {ISCAL} method and the Grounding Line - Combining the
{S}tokes equations with the Shallow Ice Approximation and
Shelfy Stream Approximation},
institution = it,
department = tdb,
year = 2016,
number = {2016-006},
month = apr,
abstract = {The Ice Sheet Coupled Approximation Level (ISCAL) method
is extended so that the non-linear Stokes equations
governing ice sheet flow are coupled with a hybrid model.
The hybrid model is a combination of the Shallow Ice
Approximation (SIA) and the Shelfy Stream Approximation
(SSA). The Stokes equations are only solved where the
hybrid model is inaccurate, which is determined by an
automatic error estimation. The method is tested on short
simulations of coupled ice sheet/ice shelf flow. The ISCAL
method applies the SIA in the high friction inland areas,
the SSA at the margins and the shelf, and the Stokes
equation at the grounding line, and occasionally at the
dome. A method for static load balancing of the ISCAL
method is proposed. }
}
@TechReport{ it:2016-005,
author = {Josefin Ahlkrona and Victor Shcherbakov},
title = {A Meshfree Approach to Non-{N}ewtonian Free Surface Ice
Flow: Application to the {H}aut {G}lacier d~{A}rolla},
institution = it,
department = tdb,
year = 2016,
number = {2016-005},
month = apr,
abstract = {Numerical models of glacier and ice sheet dynamics
traditionally employ finite difference or finite element
methods. Although these are highly developed and mature
methods, they suffer from some drawbacks, such as inability
to handle complex geometries (finite differences) or a
costly assembly procedure for nonlinear problems (finite
elements). Additionally, they are mesh-based, and therefore
moving domains become a challenge. In this paper, we
introduce a novel meshfree approach based on a radial basis
function (RBF) method. The meshfree nature of RBF methods
enables efficient handling of moving margins and free ice
surface. RBF methods are also highly accurate, easy to
implement, and allow for reduction the computational cost
associated with the linear system assembly, since stated in
strong form. To demonstrate the global RBF method we model
the velocity field of ice flow in the Haut Glacier
d'Arolla, which is governed by the nonlinear Stokes
equations. We test the method for different basal
conditions and for a free moving surface. We also compare
the global RBF method with its localized counterpart---the
RBF partition of unity method (RBF--PUM)---that allows for
a significant gain in the computational efficiency. We find
that the RBF methods are well suited for ice dynamics
modelling, especially the partition of unity approach.}
}
@TechReport{ it:2016-004,
author = {Nikos Nikoleris and Andreas Sandberg and Erik Hagersten
and Trevor E. Carlson},
title = {Implementing Fast, Virtualized Profiling to Eliminate
Cache Warming},
institution = it,
department = docs,
year = 2016,
number = {2016-004},
month = mar,
abstract = {Simulation is an important part of the evaluation of
next-generation computing systems. Detailed, cycle-level
simulation, however, can be very slow when evaluating
realistic workloads on modern microarchitectures. Sampled
simulation (e.g., SMARTS and SimPoint) improves simulation
performance by an order of magnitude or more through the
reduction of large workloads into a small but
representative sample. Additionally, the execution state
just prior to a simulation sample can be stored into
checkpoints, allowing for fast restoration and evaluation.
Unfortunately, changes in software, architecture or
fundamental pieces of the microarchitecture (e.g.,
hardware-software co-design) require checkpoint
regeneration. The end result for co-design degenerates to
creating checkpoints for each modification, a task
checkpointing was designed to eliminate. Therefore, a
solution is needed that allows for fast and accurate
simulation, without the need for checkpoints.
Virtualized fast-forwarding proposals, like FSA, are an
alternative to checkpoints that speed up sampled simulation
by advancing the execution at near-native speed between
simulation points. They rely, however, on functional
simulation to warm the architectural state prior to each
simulation point, a costly operation for moderately-sized
last-level caches (e.g., above $8$MB). Simulating future
systems with DRAM caches of many GBs can require warming of
billions of instructions, dominating the time for
simulation and negating the benefit of virtualized
fast-forwarding.
This paper proposes CoolSim, an efficient simulation
framework that eliminates cache warming. CoolSim advances
between simulation points using virtualized
fast-forwarding, while collecting sparse memory reuse
information (MRI). The MRI is collected more than an order
of magnitude faster than functional warming. At the
simulation point, detailed simulation is used to evaluate
the design while a statistical cache model uses the
previously acquired MRI to estimate whether each memory
request hits in the cache. The MRI is an architecturally
independent metric and therefore a single profile can be
used in simulations of any size cache. We describe a
prototype implementation of CoolSim based on KVM and gem5
running $19$x faster than the state-of-the-art sampled
simulation, while it estimates the CPI of the SPEC CPU2006
benchmarks with $3.62\%$ error on average, across a wide
range of cache sizes.}
}
@TechReport{ it:2016-003,
author = {Torbj{\"o}rn Wigren},
title = {A Tradeoff Between Data Rate and Regulation Performance in
Networked Data Flow Control},
institution = it,
department = syscon,
year = 2016,
number = {2016-003},
month = jan,
abstract = {The report investigates fundamental trade-offs related to
the static regulation performance in networked control
systems with delay and saturation in the feedback loop. The
trade-offs are a consequence of required $\mathcal{L}_2$
stability of the networked system, in the limit where the
delay tends to infinity. First a relation between the
relative static regulation accuracy and the static gain of
the part of the plant that affects the disturbance is
derived. Based on this, the special case with one
directional networked flow of an arbitrary medium is
considered, where the saturation is a consequence of
assumed one-directional flow. For this case it is shown
that the trade-off becomes one between relative static
regulation accuracy and flow capacity. In the wireless case
this implies that there is a tradeoff between the relative
static regulation performance and the achievable end to end
Shannon data rate. A numerical study of a wireless transmit
queue data flow controller illustrates and validates the
discovered fundamental trade-offs and limitations.}
}
@TechReport{ it:2016-002,
author = {Stefan P{\aa}lsson and Bj{\"o}rn Victor},
title = {Proceedings fr{\aa}n 5:e Utvecklingskonferensen f{\"o}r
Sveriges ingenj{\"o}rsutbildningar},
institution = it,
year = 2016,
number = {2016-002},
month = feb,
note = {In Swedish.},
abstract = {Den 5:e utvecklingskonferensen f{\"o}r Sveriges
ingenj{\"o}rsutbildningar genomf{\"o}rdes den 18-19
november 2015 vid Uppsala universitet, Uppsala.
Arrang{\"o}r f{\"o}r konferensen var den
Teknisk-naturvetenskapliga fakulteten vid Uppsala
universitet. Konferensen har sedan 2008 arrangerats
vartannat {\aa}r, och {\"a}r en nationell konferens
specifikt f{\"o}r Sveriges ingenj{\"o}rsutbildningar.
Konferensens syfte {\"a}r att utveckla
ingenj{\"o}rsutbildningarnas kvalitet genom att
underl{\"a}tta kommunikation och fr{\"a}mja samarbete.
Konferensen ska i f{\"o}rsta hand identifiera och diskutera
aktuella och gemensamma fr{\aa}gor, det vill s{\"a}ga ge
m{\"o}jlighet till erfarenhetsutbyte kring utveckling av
ingenj{\"o}rsutbildning snarare {\"a}n att vara en
traditionellt vetenskaplig konferens f{\"o}r rapportering
av forskning om ingenj{\"o}rsutbildning.
Huvudansvaret f{\"o}r Utvecklingskonferensen ligger p{\aa}
de nationella organen RET/TUF-gruppen f{\"o}r
civilingenj{\"o}rsutbildning tillsammans med
Samverkansgruppen f{\"o}r
h{\"o}gskoleingenj{\"o}rsutbildningar. De tidigare
konferenserna har h{\aa}llits vid KTH 2008, Lunds Tekniska
h{\"o}gskola 2009, Link{\"o}pings universitet 2011 och
Ume{\aa} universitet 2013. N{\"a}sta utvecklingskonferens
{\"a}r planerad till Chalmers tekniska h{\"o}gskola 2017.
M{\aa}lgruppen f{\"o}r konferensen {\"a}r l{\"a}rare inom
ingenj{\"o}rsutbildningar, personer aktiva inom
programledning f{\"o}r ingenj{\"o}rsutbildning (exempelvis
programansvariga, administrat{\"o}rer, studiev{\"a}gledare,
studentrepresentanter), och pedagogiska ledare och
utvecklare inom ingenj{\"o}rsutbildning. Konferensens teman
inkluderade bl.a. aktivt l{\"a}rande, ingenj{\"o}rsrollen och programutveckling. }
}
@TechReport{ it:2016-001,
author = {Marco Donatelli and Ali Dorostkar and Mariarosa Mazza and
Maya Neytcheva and Stefano Serra-Capizzano},
title = {A Block Multigrid Strategy for Two-Dimensional Coupled
{PDE}s},
institution = it,
department = tdb,
year = 2016,
number = {2016-001},
month = jan,
abstract = {We consider the solution of linear systems of equations,
arising from the finite element approximation of coupled
differential boundary value problems. Letting the fineness
parameter tend to zero gives rise to a sequence of large
scale structured two-by-two block matrices. We are
interested in the efficient iterative solution of the so
arising linear systems, aiming at constructing optimal
preconditioning methods that are robust with respect to the
relevant parameters of the problem. We consider the case
when the originating systems are solved by a preconditioned
Krylov method, as inner solver, and propose an efficient
preconditioner for that, based on the Generalized Locally
Toeplitz framework.
In this paper, we exploit the almost two-level block
Toeplitz structure of the arising block matrix. We provide
a spectral analysis of the underlying matrices and then, by
exploiting the spectral information, we design a multigrid
method with an ad hoc grid transfer operator. As shown in
the included examples, choosing the damped Jacobi or
Gauss-Seidel methods as smoothers and using the resulting
solver as a preconditioner leads to a competitive strategy
that outperforms some aggregation-based algebraic multigrid
methodss, widely employed in the relevant literature.}
}
@TechReport{ it:2015-038,
author = {Sven-Olof Nystr{\"o}m},
title = {Subtyping and Algebraic Data Types},
institution = it,
department = csd,
year = 2015,
number = {2015-038},
month = dec,
abstract = {We present a new method for type inference. Traditional
approaches rely on an inductively defined domain of types.
Instead, we specify the properties of the type system as a
set of axioms, and give a polynomial-time algorithm for
checking whether there is any domain of types for which the
program types. We show the correctness of the algorithm and
also prove that safety properties are satisfied; any
program accepted by the type system will not cause type
errors at run-time.
The advantages of our approach is that is simpler and more
general. The algorithm for checking that a program types is
a simple mechanism for propagating type information which
should be easy to extend to support other programming
language features. The type checking algorithm is more
general than other approaches as the algorithm will accept
any program that types under any type system that satisfies
the axioms.
We also show how to make type information available to
compilers and other development tools through an algorithm
to determine entailment.
The language we consider is lambda calculus extended with a
constructors and a form of type construct we call
\emph{open case expressions}. Open case expressions allow a
program to manipulate abstract data types where the sets of
constructors overlap.}
}
@TechReport{ it:2015-037,
author = {Muneeb Khan and David Black-Schaffer and Erik Hagersten},
title = {{P}erf-{I}nsight: A Simple, Scalable Approach to Optimal
Data Prefetching in Multicores},
institution = it,
department = docs,
year = 2015,
number = {2015-037},
month = dec,
abstract = {Aggressive hardware prefetching is extremely beneficial
for single-threaded performance but can lead to significant
slowdowns in multicore processors due to oversubscription
of off-chip bandwidth and shared cache capacity. This work
addresses this problem by adjusting prefetching on a
per-application basis to improve overall system
performance. Unfortunately, an exhaustive search of all
possible per-application prefetching combinations for a
multicore workload is prohibitively expensive, even for
small processors with only four cores.
In this work we develop Perf-Insight, a simple, scalable
mechanism for understanding and predicting the impact of
any available hardware/software prefetching choices on
applications' bandwidth consumption and performance. Our
model considers the overall system bandwidth, the bandwidth
sensitivity of each co-running application, and how
applications' bandwidth usage and performance vary with
prefetching choices. This allows us to profile individual
applications and efficiently predict total system bandwidth
and throughput. To make this practical, we develop a
low-overhead profiling approach that scales linearly,
rather than exponentially, with the number of cores, and
allows us to profile applications while running in the mix.
With Perf-Insight we are able to achieve an average
weighted speedup of 21\% for 14 mixes of 4 applications on
commodity hardware, with no mix experiencing a slowdown.
This is significantly better than hardware prefetching,
which only achieves an average speedup of 9\%, with three
mixes experiencing slowdowns. Perf-Insight delivers
performance very close to the best possible prefetch
settings (22\%). Our approach is simple, low-overhead,
applicable to any collection of prefetching options and
performance metric, and suitable for dynamic runtime use on
commodity multicore systems.}
}
@TechReport{ it:2015-036,
author = {Owe Axelsson and Shiraz Farouq and Maya Neytcheva},
title = {A Preconditioner for Optimal Control Problems, Constrained
by {S}tokes Equation with a Time-Harmonic Control},
institution = it,
department = tdb,
year = 2015,
number = {2015-036},
month = dec,
abstract = {In an earlier paper preconditioning of stationary
Stokes-constrained optimal control problems has been
considered.
In this article we construct an efficient preconditioner
for solving the algebraic systems arising from discretized
optimal control problems with time-periodic Stokes
equations. A simplified analysis of the derivation of the
preconditioner and its properties is presented. The
reconditioner is fully parameter independent and the
condition number of the corresponding preconditioned matrix
is bounded by $2$. The o-constructed preconditioner is
favourably compared with another preconditioner for the
same problem.}
}
@TechReport{ it:2015-035,
author = {Johan {\"O}fverstedt and Per Normann},
title = {Deterministic Parallel Graph Coloring with Repartitioning
by Auxiliary Graph Coloring},
institution = it,
department = tdb,
year = 2015,
number = {2015-035},
month = dec,
abstract = {In this paper we propose a deterministic parallel graph
coloring algorithm that enables Multi-Coloring in parallel
for sparse undirected graphs by coarse-grained segmentation
and auxiliary graph coloring. The proposed algorithm is
implemented and tested on standard problem instances from
engineering applications and benchmarked against various
relevant deterministic graph coloring algorithms.
Quantified results show that the proposed algorithm is
competitive or better than the sequential Multi-Coloring
algorithm with respect to execution time on multi-core
architectures. The upper bound on the number of colors is
guaranteed to be the same as for the Multi-Coloring
algorithm.}
}
@TechReport{ it:2015-034,
author = {Adriaan Larmuseau and Marco Patrignani and Dave Clarke},
title = {Implementing a Secure Abstract Machine -- Extended
Version},
institution = it,
department = csd,
year = 2015,
number = {2015-034},
month = nov,
note = {This technical report serves as the companion report to a
SEC@SAC 2016 paper of the same name.},
abstract = {Abstract machines are both theoretical models used to
study language properties and practical models of language
implementations. As with all language implementations,
abstract machines are subject to security violations by the
context in which they reside. This paper presents the
implementation of an abstract machine for ML that preserves
the abstractions of the language it implements, in possibly
malicious, low-level contexts. To guarantee this security
result, we make use of a low-level memory isolation
mechanism and derive the formalisation of the machine
through a methodology, whose every step is accompanied by
formal properties that ensure that the step has been
carried out properly. We provide an implementation of the
abstract machine and analyse its performance for relevant
scenarios.}
}
@TechReport{ it:2015-033,
author = {Volkan Cambazoglu and Ram{\=u}nas Gutkovas and Johannes
{\AA}man Pohjola and Bj{\"o}rn Victor},
title = {Modelling and Analysing a WSN Secure Aggregation Protocol:
A Comparison of Languages and Tool Support},
institution = it,
year = 2015,
number = {2015-033},
month = nov,
note = {Updated 2015-12-02: The results in subsection 4.1.3 are
updated because we realised that Pwb can evaluate the SHIA
model faster for network sizes of 2 and 4, and also can
handle network size of 8.},
abstract = {A security protocol promises protection of a significant
piece of information while using it for a specific purpose.
Here, the protection of the information is vital and a
formal verification of the protocol is an essential step
towards guaranteeing this protection. In this work, we
study a secure aggregation protocol (SHIA) for Wireless
Sensor Networks and verify the protocol in three formal
modelling tools (Pwb, mCRL2 and ProVerif). The results of
formal verification heavily depend on the model
specification and the ability of the tools to deal with the
model. Among the three tools, there is difference in data
representation, communication types and the level of
abstraction in order to represent SHIA. ProVerif and mCRL2
are mature and well-established tools, geared respectively
towards security and distributed systems; however, their
expressiveness constrains modelling SHIA and its security
properties. Pwb is an experimental tool developed by the
authors; its relative immaturity is offset by its increased
expressive power and customisability. This leads to
different models of the same protocol, each contributing in
different ways to our understanding of SHIA's security
properties.}
}
@TechReport{ it:2015-032,
author = {Sofia Cassel and Falk Howar and Bengt Jonsson and Bernhard
Steffen},
title = {Active Learning for Extended Finite State Machines},
institution = it,
department = docs,
year = 2015,
number = {2015-032},
month = oct,
note = {This report updates and supercedes Technical Report
2015-004.},
abstract = {We present a black-box active learning algorithm for
inferring extended finite state machines (EFSM)s, combining
data flow and control behavior. Different dialects of EFSMs
are widely used in tools for model-based software
development, verification, and testing. Our algorithm
infers a class of EFSMs called \emph{register automata}.
Register automata have a finite control structure, extended
with variables (registers), assignments, and guards. Our
algorithm is parameterized on a particular theory, i.e., a
set of operations and tests on the data domain that can be
used in guards.
Key to our learning technique is a novel learning model
based on so-called \emph{tree queries}. The learning
algorithm uses the tree queries to infer symbolic data
constraints on parameters, e.g., sequence numbers, time
stamps, identifiers, or even simple arithmetic. We describe
sufficient conditions for the properties that the symbolic
constraints provided by a tree query in general must have
to be usable in our learning model. We also show that,
under these conditions, our framework induces a
generalization of the classical Nerode equivalence and
canonical automata construction to the symbolic setting. We
have evaluated our algorithm in a black-box scenario, where
tree queries are realized through (black-box) testing. Our
case studies include connection establishment in TCP and a
priority queue from the Java Class Library.}
}
@TechReport{ it:2015-031,
author = {Per Normann and Johan {\"O}fverstedt},
title = {Deterministic Parallel Graph Coloring with Symmetry
Breaking},
institution = it,
department = tdb,
year = 2015,
number = {2015-031},
month = oct,
abstract = {In this paper we propose a deterministic parallel graph
coloring algorithm that enables Multi-Coloring in parallel
for sparse undirected graphs by coarse-grained segmentation
and symmetry breaking. The proposed algorithm is
implemented and tested on standard problem instances from
engineering applications and benchmarked against various
deterministic graph coloring algorithms. Quantified results
show that the proposed algorithm is competitive or better
than the sequential Multi-Coloring algorithm with respect
to execution time on multi-core architectures. The upper
bound on the number of colors is guaranteed to be the same
as for the Multi-Coloring algorithm.}
}
@TechReport{ it:2015-030,
author = {Owe Axelsson and Shiraz Farouq and Maya Neytcheva},
title = {Comparison of preconditioned {K}rylov subspace iteration
methods for {PDE}-constrained optimization problems.
{S}tokes control},
institution = it,
department = tdb,
year = 2015,
number = {2015-030},
month = sep,
abstract = {The governing dynamics of fluid flow is stated as a system
of partial differential equations referred to as the
Navier-Stokes system. In industrial and scientific
applications, fluid flow control becomes an optimization
problem where the governing partial differential equations
of the fluid flow are stated as constraints. When
discretized, the optimal control of the Navier-Stokes
equations leads to large sparse saddle point systems in two
levels.
In this paper we consider distributed optimal control for
the Stokes system and test the particular case when the
arising linear system can be compressed after eliminating
the control function. In that case, a system arises in a
form which enables the application of an efficient block
matrix preconditioner that previously has been applied to
solve complex-valued systems in real arithmetic. Under
certain conditions the condition number of the so
preconditioned matrix is bounded by 2. The numerical and
computational efficiency of the method in terms of number
of iterations and execution time is favorably compared with
other published methods.}
}
@TechReport{ it:2015-029,
author = {Kjellin Lagerqvist, Nanna},
title = {Resultat och reflektioner kring mailkategorisering av
anv{\"a}ndares mail till Uppsala l{\"a}ns landsting kring
{\aa}tkomst av journaler via n{\"a}tet},
institution = it,
department = docs,
year = 2015,
number = {2015-029},
month = sep,
note = {In Swedish. Updates and supercedes Technical Report nr
2015-010.},
abstract = {P{\aa} uppdrag av Benny Eklund, Uppsala l{\"a}ns
landsting, har mail inkomna till mailboxen med adress
sustains@lul.se under fj{\"a}rde kvartalet 2012 till och
med f{\"o}rsta kvartalet 2014 l{\"a}sts och kategoriserats.
Mailboxens syfte har varit att motta feedback fr{\aa}n
anv{\"a}ndare av Sustains, senare Journalen. Nedan
ben{\"a}mns b{\aa}da versionerna av systemet vid
samlingsnamnet Journal via n{\"a}tet. Feedbacken var av
typen fritt formulerade {\aa}sikter och erfarenheter.
Anv{\"a}ndarna har inte anv{\"a}nt n{\aa}gon mall eller
svarat p{\aa} n{\aa}gra specifika fr{\aa}gor utan har
ombetts ber{\"a}tta fritt om sina upplevelser.
Under den iterativa genomg{\aa}ngen av mailen utformades
fjorton kategorier utifr{\aa}n vilka anv{\"a}ndarnas
feedback sorterades. Resultatet av detta visade att de
flesta anv{\"a}ndare var positiva till Journal via
n{\"a}tet och det fr{\"a}msta anv{\"a}ndningsomr{\aa}det
var som minnesanteckning och komplement till ett tidigare
v{\aa}rdbes{\"o}k. {\"A}ven anv{\"a}ndare som inte hade
n{\aa}gon v{\aa}rdkontakt i Uppsala l{\"a}n, och
d{\"a}rf{\"o}r inte s{\aa}g n{\aa}got inneh{\aa}ll i
journalen, var positiva till tj{\"a}nsten och efterfr{\aa}gade den till sina landsting.}
}
@TechReport{ it:2015-028,
author = {Adriaan Larmuseau and Marco Patrignani and Dave Clarke},
title = {A Secure Compiler for {ML} Modules - Extended Version},
institution = it,
department = csd,
year = 2015,
number = {2015-028},
month = sep,
note = {This technical report is an updated version of TR 2015-017
that serves as the companion report to an APLAS 2015 paper
of the same title.},
abstract = {Many functional programming languages compile to low-level
languages such as C or assembly. Most security properties
of those compilers, however, apply only when the compiler
compiles whole programs. This paper presents a compilation
scheme that securely compiles a standalone module of
ModuleML, a light-weight version of an ML with modules,
into untyped assembly. The compilation scheme is secure in
that it reflects the abstractions of a ModuleML module, for
every possible piece of assembly code that it interacts
with. This is achieved by isolating the compiled module
through a low-level memory isolation mechanism and by
dynamically type checking the low-level interactions. We
evaluate an implementation of the compiler on relevant test
scenarios.}
}
@TechReport{ it:2015-027,
author = {Umberto Soverini and Torsten S{\"o}derstr{\"o}m},
title = {Frequency Domain Identification of Autoregressive Models
in the Presence of Additive Noise},
institution = it,
department = syscon,
year = 2015,
number = {2015-027},
month = sep,
abstract = {This paper describes a new approach for identifying
autoregressive models from a finite number of measurements,
in presence of additive and uncorrelated white noise. As a
major novelty, the proposed approach deals with frequency
domain data. In particular, two different frequency domain
algorithms are proposed. The first algorithm is based on
some theoretical results concerning the so--called dynamic
Frisch Scheme. The second algorithm maps the AR
identification problem into a quadratic eigenvalue problem.
Both methods resemble in many aspects some other
identification algorithms, originally developed in the time
domain. The features of the proposed methods are compared
to each other and with those of other time domain
algorithms by means of Monte Carlo simulations.}
}
@TechReport{ it:2015-026,
author = {Adriaan Larmuseau and Dave Clarke},
title = {Modelling an Assembly Attacker by Reflection},
institution = it,
department = csd,
year = 2015,
number = {2015-026},
month = aug,
note = {This technical report is an extended version of a paper
titled: \emph{A High-Level Model for an Assembly Language
Attacker by means of Reflection} that is to appear at SETTA
2015.},
abstract = {Many high-level functional programming languages are
compiled to or interoperate with, low-level languages such
as C and assembly. Research into the security of these
compilation and interoperation mechanisms often makes use
of high-level attacker models to simplify formalisations.
In practice, however, the validity of such high-level
attacker models is frequently called into question. In this
technical report we formally prove that a light-weight
ML-like including references, equipped with a reflection
operator can serve as an accurate model for malicious
assembly language programs, when reasoning about the
security threats posed to the abstractions of high-level
functional programs that reside within a protected memory
space. The proof proceeds by relating a bisimulation over
the inputs and observations of the assembly language
attacker to a bisimulation over the inputs and observations
of the high-level attacker.}
}
@TechReport{ it:2015-025,
author = {Fritjof Fagerlund and Fredrik Hellman and Axel
M{\aa}lqvist and Auli Niemi},
title = {Improved {M}onte {C}arlo Methods for Computing Failure
Probabilities of Porous Media Flow Systems},
institution = it,
department = tdb,
year = 2015,
number = {2015-025},
month = aug,
abstract = {We study improvements of standard and multilevel Monte
Carlo methods for point evaluation of the cumulative
distribution function (failure probability) applied to
porous media two-phase flow simulations with uncertain
permeability. In an injection scenario with sweep
efficiency of the injected phase as quantity of interest,
we seek the probability that this quantity of interest is
smaller than a critical value. In the sampling procedure,
we use computable error bounds on the sweep efficiency
functional to solve only a subset of all realizations to
highest accuracy by means of what we call selective
refinement. We quantify the performance gains possible by
using selective refinement in combination with both the
standard and multilevel Monte Carlo method. We also
identify issues in the process of practical implementation
of the methods. We conclude that significant savings (one
order of magnitude) in computational cost are possible for
failure probability estimation in a realistic setting using
the selective refinement technique, both in combination
with standard and multilevel Monte Carlo.}
}
@TechReport{ it:2015-024,
author = {Owe Axelsson and Shiraz Farouq and Maya Neytcheva},
title = {Comparison of Preconditioned {K}rylov Subspace Iteration
Methods for {PDE}-Constrained Optimization Problems.
{P}oisson and Convection-Diffusion Control},
institution = it,
department = tdb,
year = 2015,
number = {2015-024},
month = aug,
abstract = {Saddle point matrices of a special structure arise in
optimal control problems. In this paper we consider
distributed optimal control for various types of scalar
stationary partial differential problems and compare the
efficiency of several numerical solution methods. We test
the particular case when the arising linear system can be
compressed after eliminating the control function. In that
case, a system arises in a form which enables application
of an efficient block matrix preconditioner that previously
has been applied to solve complex-valued systems in real
arithmetic. Under certain conditions the condition number
of the so preconditioned matrix is bounded by 2. The
numerical and computational efficiency of the method in
terms of number of iterations and elapsed time is favorably
compared with other published methods. }
}
@TechReport{ it:2015-023,
author = {Carlo Garoni and Stefano Serra-Capizzano},
title = {The theory of {G}eneralized {L}ocally {T}oeplitz
sequences: a review, an extension, and a few representative
applications},
institution = it,
department = tdb,
year = 2015,
number = {2015-023},
month = aug,
note = {Revised, corrected, updated and extended version of TR
2015-016.},
abstract = {We review and extend the theory of Generalized Locally
Toeplitz (GLT) sequences, which goes back to the pioneering
work by Tilli on Locally Toeplitz (LT) sequences and was
developed by the second author during the last decade.
Informally speaking, a GLT sequence $\{A_n\}_n$ is a
sequence of matrices with increasing size, equipped with a
Lebesgue-measurable function $\kappa$ (the so-called
symbol). This function characterizes the asymptotic
singular value distribution of $\{A_n\}_n$; in the case
where the matrices $A_n$ are Hermitian, it also
characterizes the asymptotic eigenvalue distribution of
$\{A_n\}_n$. Three fundamental examples of GLT sequences
are: (i) the sequence of Toeplitz matrices generated by a
function $f$ in $L^1$; (ii) the sequence of diagonal
sampling matrices containing the evaluations of a
Riemann-integrable function $a$ over a uniform grid; (iii)
any zero-distributed sequence, i.e., any sequence of
matrices possessing an asymptotic singular value
distribution characterized by the identically zero
function. The symbol of the GLT sequence (i) is $f$, the
symbol of the GLT sequence (ii) is $a$, and the symbol of
any GLT sequence of the form (iii) is 0. The set of GLT
sequences is a *-algebra. More precisely, suppose that
$\{A_n^{(1)}\}_n,\ldots,\{A_n^{(r)}\}_n$ are GLT sequences
with symbols $\kappa_1,\ldots,\kappa_r$, and let
$A_n=\textup{ops}(A_n^{(1)},\ldots,A_n^{(r)})$ be a matrix
obtained from $A_n^{(1)},\ldots,A_n^{(r)}$ by means of
certain algebraic operations `ops', such as linear
combinations, products, inversions and Hermitian
transpositions; then, $\{A_n\}_n$ is a GLT sequence with
symbol $\kappa=\textup{ops}(\kappa_1,\ldots,\kappa_r)$.
As already proved in several contexts, the theory of GLT
sequences is a powerful apparatus for computing the
asymptotic singular value and eigenvalue distribution of
the discretization matrices $A_n$ arising from the
numerical approximation of continuous problems, such as
integral equations and, especially, partial differential
equations. Indeed, when the discretization parameter $n$
tends to infinity, the discretization matrices $A_n$ give
rise to a sequence $\{A_n\}_n$, which often turns out to be
a GLT sequence.
However, in this work we are not concerned with the
applicative interest of the theory of GLT sequences, for
which we limit to outline some of the numerous applications
and to refer the reader to the available literature. On the
contrary, we focus on the mathematical foundations. We
propose slight (but relevant) modifications of the original
definitions, and we introduce for the first time the
concept of LT sequences in the multivariate/multilevel
setting. With the new definitions, based on the notion of
approximating class of sequences, we are able to enlarge
the applicability of the theory, by generalizing and/or
simplifying a lot of key results. In particular, we remove
a technical hypothesis concerning the Riemann-integrability
of the so-called `weight functions', which appeared in the
statement of many spectral distribution and algebraic
results for GLT sequences. Moreover, we provide a formal
and detailed proof of the fact that the sequences of
matrices mentioned in items (i)--(iii) fall in the class of
LT sequences. Several versions of this result were already
present in previous papers, but only partial proofs were
given.
As a final step, we extend the theory of GLT sequences. We
first prove an approximation result, which is particularly
useful to show that a given sequence of matrices is a GLT
sequence. By using this result, we provide a new and easier
proof of the fact that $\{A_n^{-1}\}_n$ is a GLT sequence
with symbol $\kappa^{-1}$ whenever $\{A_n\}_n$ is a GLT
sequence of invertible matrices with symbol $\kappa$ and
$\kappa\ne 0$ almost everywhere. Finally, using again the
approximation result, we prove that $\{f(A_n)\}_n$ is a GLT
sequence with symbol $f(\kappa)$, as long as
$f:\mathbb{R}\to\mathbb{R}$ is continuous and $\{A_n\}_n$
is a GLT sequence of Hermitian matrices with symbol
$\kappa$. This has important implications, e.g., in proving
that the geometric mean of two GLT sequences is still a GLT
sequence, with symbol given by the the geometric mean of the symbols.}
}
@TechReport{ it:2015-022,
author = {Tomas Wilkinson and Anders Brun},
title = {Experiments on Large Scale Document Visualization using
Image-based Word Clouds},
institution = it,
department = vi2,
year = 2015,
number = {2015-022},
month = jul,
abstract = {In this paper, we introduce image-based word clouds as a
novel tool for a quick and aesthetic overviews of common
words in collections of digitized text manuscripts. While
OCR can be used to enable summaries and search
functionality to printed modern text, historical and
handwritten documents remains a challenge. By segmenting
and counting word images, without applying manual
transcription or OCR, we have developed a method that can
produce word- or tag clouds from document collections. Our
new tool is not limited to any specific kind of text. We
make further contributions in ways of stop-word removal,
class based feature weighting and visualization. An
evaluation of the proposed tool includes comparisons with
ground truth word clouds on handwritten marriage licenses
from the 17th century and the George Washington database of
handwritten letters, from the 18th century. Our experiments
show that image-based word clouds capture the same
information, albeit approximately, as the regular word
clouds based on text data.}
}
@TechReport{ it:2015-021,
author = {Joachim Parrow and Johannes Borgstr{\"o}m and Lars-Henrik
Eriksson and Ram{\=u}nas Gutkovas and Tjark Weber},
title = {Modal Logics for Nominal Transition Systems},
institution = it,
department = csd,
year = 2015,
number = {2015-021},
month = jun,
note = {Accepted for CONCUR 2015. This version includes proofs in
an appendix.},
abstract = {We define a uniform semantic substrate for a wide variety
of process calculi where states and action labels can be
from arbitrary nominal sets. A Hennessy-Milner logic for
these systems is introduced, and proved adequate for
bisimulation equivalence. A main novelty is the use of
finitely supported infinite conjunctions. We show how to
treat different bisimulation variants such as early, late
and open in a systematic way, and make substantial
comparisons with related work. The main definitions and
theorems have been formalized in Nominal Isabelle. }
}
@TechReport{ it:2015-020,
author = {Per Normann and Johan {\"O}fverstedt},
title = {Deterministic Parallel Graph Coloring with Hashing},
institution = it,
department = tdb,
year = 2015,
number = {2015-020},
month = jun,
abstract = {In this paper we propose a new deterministic parallel
graph coloring algorithm. Parallelism is achieved by
distribution of vertices to processors by hashing. The
hashing is based on markers assigned to each conflict prone
vertex.}
}
@TechReport{ it:2015-019,
author = {Andreas Svensson and Thomas B Sch{\"o}n and Manon Kok},
title = {Some Details on State Space Smoothing using the
Conditional Particle Filter},
institution = it,
department = syscon,
year = 2015,
number = {2015-019},
month = jun,
abstract = {This technical report gives some additional details on the
numerical examples used in \emph{Nonlinear state space
smoothing using the conditional particle filter}, by the
same authors, published in Proceedings of the 17th IFAC
Symposium on System Identication (SYSID), Beijing, China,
October 2015.}
}
@TechReport{ it:2015-018,
author = {Johannes Nygren and Torbj{\"o}rn Wigren and Kristiaan
Pelckmans},
title = {Delay-Independent Stability Criteria for Networked Control
Systems},
institution = it,
department = syscon,
year = 2015,
number = {2015-018},
month = jun,
abstract = {The report analyses a networked control system consisting
of a LTI system coupled with a static nonlinearity, subject
to large delays in the feedback loop. This model is valid
for example in wireless data flow control, where a
saturation occurs since the flow is one-directional. The
present report extends previous results by proving
necessity, in case the loop gain is uniformly less than 1.
The results are validated and illustrated in a simulation
study.}
}
@TechReport{ it:2015-017,
author = {Adriaan Larmuseau and Marco Patrignani and Dave Clarke},
title = {A Secure Compiler for {ML} Modules - Extended Version},
institution = it,
department = csd,
year = 2015,
number = {2015-017},
month = jun,
abstract = {Many functional programming languages compile to low-level
languages such as C or assembly. Most security properties
of those compilers, however, apply only when the compiler
compiles whole programs. This paper presents a compilation
scheme that securely compiles a standalone module of
ModuleML, a light-weight version of an ML with modules,
into untyped assembly. The compilation scheme is secure in
that it reflects the abstractions of a ModuleML module, for
every possible piece of assembly code that it interacts
with. This is achieved by isolating the compiled module
through a low-level memory isolation mechanism and by
dynamically type checking the low-level interactions. We
evaluate an implementation of the compiler on relevant test
scenarios.}
}
@TechReport{ it:2015-016,
author = {Carlo Garoni and Stefano Serra-Capizzano},
title = {{G}eneralized {L}ocally {T}oeplitz sequences: a review and
an extension},
institution = it,
department = tdb,
year = 2015,
number = {2015-016},
month = may,
note = {Revised, corrected, updated and extended by TR 2015-023
(\url{http://www.it.uu.se/research/publications/reports/2015-023}).}
,
abstract = {We review the theory of Generalized Locally Toeplitz (GLT)
sequences, hereinafter called `the GLT theory', which goes
back to the pioneering work by Tilli on Locally Toeplitz
(LT) sequences and was developed by the second author
during the last decade: every GLT sequence has a measurable
symbol; the singular value distrbution of any GLT sequence
is identified by the symbol (also the eigenvalue
distribution if the sequence is made by Hermitian
matrices); the GLT sequences form an algebra, closed under
linear combinations, (pseudo)-inverse if the symbol
vanishes in a set of zero measure, product and the symbol
obeys to the same algebraic manipulations.
As already proved in several contexts, this theory is a
powerful tool for computing/analyzing the asymptotic
spectral distribution of the discretization matrices
arising from the numerical approximation of continuous
problems, such as Integral Equations and, especially,
Partial Differential Equations, including variable
coefficients, irregular domains, different approximation
schemes such as Finite Differences, Finite Elements,
Collocation/Galerkin Isogeometric Analysis etc.
However, in this review we are not concerned with the
applicative interest of the GLT theory, for which we limit
to refer the reader to the numerous applications available
in the literature.
On the contrary, we focus on the theoretical foundations.
We propose slight (but relevant) modifications of the
original definitions, which allow us to enlarge the
applicability of the GLT theory. In particular, we remove a
certain `technical' hypothesis concerning the
Riemann-integrability of the so-called `weight functions',
which appeared in the statement of many spectral
distribution and algebraic results for GLT sequences.
With the new definitions, we introduce new technical and
useful results and we provide a formal proof of the fact
that sequences formed by multilevel diagonal sampling
matrices, as well as multilevel Toeplitz sequences, fall in
the class of LT sequences; the latter results were
mentioned in previous papers, but no direct proof was given
especially regarding the case of multilevel diagonal
sampling matrix-sequences.
As a final step, we extend the GLT theory: we first prove
an approximation result, which is particularly useful to
show that a given sequence of matrices is a GLT sequence;
by using this result, we provide a new and easier proof of
the fact that $\{A_n^{-1}\}_n$ is a GLT sequence with
symbol $\kappa^{-1}$ whenever $\{A_n\}_n$ is a GLT sequence
of invertible matrices with symbol $\kappa$ and $\kappa\ne
0$ almost everywhere; finally, using again the
approximation result, we prove that $\{f(A_n)\}_n$ is a GLT
sequence with symbol $f(\kappa)$, as long as
$f:\mathbb{R}\to\mathbb{R}$ is continuous and $\{A_n\}_n$
is a GLT sequence of Hermitian matrices with symbol
$\kappa$.
This latter theoretical property has important
implications, e.g. in proving that the geometric means of
GLT sequences are still GLT, so obtaining for free that the
spectral distribution of the mean is just the geometric
mean of the symbols.}
}
@TechReport{ it:2015-015,
author = {Adriaan Larmuseau and Dave Clarke},
title = {Formalizing a Secure Foreign Function Interface - Extended
Version},
institution = it,
department = csd,
year = 2015,
number = {2015-015},
month = may,
note = {This technical report is an extended version of the paper
of the same name that is to appear at SEFM 2015.},
abstract = {Many high-level functional programming languages provide
programmers with the ability to interoperate with untyped
and low-level languages such as C and assembly. Research
into such interoperation has generally focused on a closed
world scenario, one where both the high-level and low-level
code are defined and analyzed statically. In practice,
however, components are sometimes linked in at run-time
through malicious means. In this paper we formalize an
operational semantics that securely combines MiniML, a
light-weight ML, with a model of a low-level attacker,
without relying on any static checks. We prove that the
operational semantics are secure by establishing that they
preserve and reflect the equivalences of MiniML. To that
end a notion of bisimulation for the interaction between
the attacker and MiniML is developed.}
}
@TechReport{ it:2015-014,
author = {Timofey Mukha and Mattias Liefvendahl},
title = {Large-Eddy Simulation of Turbulent Channel Flow},
institution = it,
department = tdb,
year = 2015,
number = {2015-014},
month = may,
abstract = {Channel flow, at $Re_{\tau}\approx 395$, has been computed
using large-eddy simulation (LES) and the general-purpose
software \texttt{OpenFOAM}. The purpose of the study is to
evaluate the applicability of \texttt{OpenFOAM} for
modelling wall-bounded turbulent flows, of which channel
flow is a canonical example. A wide range of statistical
quantities is reported, which includes: the mean velocity;
the fluctuations of velocity; the turbulent shear stress;
higher order statistical moments, skewness and flatness;
the fluctuations of vorticity; spatial two-point
correlations of velocity fluctuations. The results are
compared with data obtained using direct numerical
simulation (DNS). The simulations are carried out on three
grid refinement levels and a detailed analysis of how the
grid size affects the solution is given. The general
conclusion that can be drawn is that \texttt{OpenFOAM} can
be successfully used for LES of wall-bounded flows. The
investigation of grid convergence showed that even
relatively coarse grids can be used if only first order
statistics are of interest. However, for higher order
statistical moments, the gain of using finer grids is evident.}
}
@TechReport{ it:2015-013,
author = {Torbj{\"o}rn Wigren},
title = {Constraints in nonlinear $\mathcal{L}_2$-stable networked
control},
institution = it,
department = syscon,
year = 2015,
number = {2015-013},
month = may,
abstract = {The report derives a robust networked controller design
method for systems with saturation where the delay is large
and unknown, as in unidirectional flow-control. A classical
linear robust criterion is first formulated in terms of the
sensitivity- and complementary sensitivity functions. Based
on the Popov-criterion a new asymptotic constraint is
derived, which specifies the minimum amount of low
frequency gain in the sensitivity function, to guarantee
non-linear closed loop $\mathcal{L}_2$-stability. This
result guides the selection of the design criterion,
thereby adjusting the linear controller design for better
handling of delay and saturation. The controller design
method then uses gridding to pre-compute the
$\mathcal{L}_2$ stability region. Based on the pre-computed
stability region, a robust $\mathcal{L}_2$-stable
controller can be selected. Alternatively, an adaptive
controller could recompute $\mathcal{L}_2$-stable
controllers on-line using the pre-computed stability
region. Simulations show that the controller meets the
specified stability and performance requirements.}
}
@TechReport{ it:2015-012,
author = {Carlo Garoni and Carla Manni and Stefano Serra-Capizzano
and Debora Sesana and Hendrik Speleers},
title = {Lusin Theorem, {GLT} Sequences and Matrix Computations: An
Application to the Spectral Analysis of {PDE}
Discretization Matrices},
institution = it,
department = tdb,
year = 2015,
number = {2015-012},
month = mar,
abstract = {We extend previous results on the spectral distribution of
discretization matrices arising from B-spline Isogeometric
Analysis (IgA) approximations of a general $d$-dimensional
second-order elliptic Partial Differential Equation (PDE)
with variable coefficients.
First, we provide the spectral symbol of the Galerkin
B-spline IgA stiffness matrices, assuming only that the PDE
coefficients belong to $L^{\infty}$. This symbol describes
the asymptotic spectral distribution when the fineness
parameters tend to zero (so that the matrix-size tends to
infinity).
Second, we prove the positive semi-definiteness of the
$d\times d$ symmetric matrix in the Fourier variables
$(\theta_1,\ldots,\theta_d)$, which appears in the
expression of the symbol. This matrix is related to the
discretization of the (negative) Hessian operator, and its
positive semi-definiteness implies the non-negativity of
the symbol.
The mathematical arguments used in our derivation are based
on the Lusin theorem, on the theory of Generalized Locally
Toeplitz (GLT) sequences, and on careful Linear Algebra
manipulations of matrix determinants.
These arguments are very general and can be also applied to
other PDE discretization techniques than B-spline IgA.}
}
@TechReport{ it:2015-011,
author = {Ali Dorostkar and Maya Neytcheva and Stefano
Serra-Capizzano},
title = {Schur Complement Matrix and its (Elementwise)
Approximation: A Spectral Analysis Based on {GLT}
Sequences},
institution = it,
department = tdb,
year = 2015,
number = {2015-011},
month = mar,
abstract = {Using the notion of the so-called \textit{spectral symbol}
in the Generalized Locally Toeplitz (GLT) setting, we
derive the GLT symbol of the sequence of matrices $\{A_n\}$
approximating the elasticity equations. Further, as the GLT
class defines an algebra of matrix sequences and Schur
complements are obtained via elementary algebraic operation
on the blocks of $A_n$, we derive the symbol
$f^{\mathcal{S}}$ of the associated sequences of Schur
complements $\{S_n\}$ and that of its element-wise
approximation. }
}
@TechReport{ it:2015-010,
author = {Kjellin Lagerqvist, Nanna},
title = {Resultat och reflektioner kring mailkategorisering av
anv{\"a}ndares mail till Uppsala l{\"a}ns landsting kring
{\aa}tkomst av journaler via n{\"a}tet},
institution = it,
department = docs,
year = 2015,
number = {2015-010},
month = mar,
note = {In Swedish. Updated and superceded by Technical Report nr
2015-029.},
abstract = {P{\aa} uppdrag av Benny Eklund, Uppsala l{\"a}ns
landsting, har mail inkomna till mailboxen med adress
sustains@lul.se under fj{\"a}rde kvartalet 2012 till och
med f{\"o}rsta kvartalet 2014 l{\"a}sts och kategoriserats.
Mailboxens syfte har varit att motta feedback fr{\aa}n
anv{\"a}ndare av Sustains, senare Journalen. Nedan
ben{\"a}mns b{\aa}da versionerna av systemet vid
samlingsnamnet Journal via n{\"a}tet. Feedbacken var av
typen fritt formulerade {\aa}sikter och erfarenheter.
Anv{\"a}ndarna har inte anv{\"a}nt n{\aa}gon mall eller
svarat p{\aa} n{\aa}gra specifika fr{\aa}gor utan har
ombetts ber{\"a}tta fritt om sina upplevelser.
Under den iterativa genomg{\aa}ngen av mailen utformades
fjorton kategorier utifr{\aa}n vilka anv{\"a}ndarnas
feedback sorterades. Resultatet av detta visade att de
flesta anv{\"a}ndare var positiva till Journal via
n{\"a}tet och det fr{\"a}msta anv{\"a}ndningsomr{\aa}det
var som minnesanteckning och komplement till ett tidigare
v{\aa}rdbes{\"o}k. {\"A}ven anv{\"a}ndare som inte hade
n{\aa}gon v{\aa}rdkontakt i Uppsala l{\"a}n, och
d{\"a}rf{\"o}r inte s{\aa}g n{\aa}got inneh{\aa}ll i
journalen, var positiva till tj{\"a}nsten och efterfr{\aa}gade den till sina landsting.}
}
@TechReport{ it:2015-009,
author = {Emilie Blanc},
title = {Approximation of the Diffusive Representation by
Decreasing Exponential Functions},
institution = it,
department = tdb,
year = 2015,
number = {2015-009},
month = feb,
abstract = {Diffusive representation of pseudo-differential operators
is a theory that has attracted interest during the last
years, and the discretization of the diffusive
representation allows significant simplifications for
numerical integration encountered in many physical models.
The feasibility of such integration relies on efficient
determination of the coefficients involved in the
representation. In this report a novel way to determine
such coefficients is proposed based on non-linear
optimization. Compared to the typical method using Gaussian
quadrature, our new approach is shown to lead to more
accurate approximation in a particular case with
application to computational biology.}
}
@TechReport{ it:2015-008,
author = {Ali Dorostkar and Maya Neytcheva and Stefano
Serra-Capizzano},
title = {Spectral Analysis of Coupled {PDE}s and of their {S}chur
Complements via the Notion of {G}eneralized {L}ocally
{T}oeplitz Sequences},
institution = it,
department = tdb,
year = 2015,
number = {2015-008},
month = feb,
abstract = {We consider large linear systems of algebraic equations
arising from the Finite Element approximation of coupled
partial differential equations. As case study we focus on
the linear elasticity equations, formulated as a saddle
point problem to allow for modeling of purely
incompressible materials. Using the notion of the so-called
\textit{spectral symbol} in the Generalized Locally
Toeplitz (GLT) setting, we derive the GLT symbol (in the
Weyl sense) of the sequence of matrices $\{A_n\}$
approximating the elasticity equations. Further, exploiting
the property that the GLT class { defines an algebra of
matrix sequences} and the fact that the Schur complements
are obtained via elementary algebraic operation on the
blocks of $A_n$, we derive the symbols $f^{\mathcal{S}}$ of
the associated sequences of Schur complements $\{S_n\}$. As
a consequence of the GLT theory, the eigenvalues of $S_n$
for large $n$ are described by a sampling of
$f^{\mathcal{S}}$ on a uniform grid of its domain of
definition. We extend the existing GLT technique with novel
elements, related to block-matrices and Schur complement
matrices, and illustrate the theoretical findings with
numerical tests. }
}
@TechReport{ it:2015-007,
author = {Aletta Nyl{\'e}n and Mohamed Shenify},
title = {Proceedings from the 1st {A}lbaha {U}niversity--{U}ppsala
{U}niversity Collaborative Symposium on Quality in
Computing Education},
institution = it,
year = 2015,
number = {2015-007},
month = feb,
abstract = {This is the proceedings from the first AlBaha University -
Uppsala University Collaborative Symposium on Quality in
Computing Education (ABU3QCE), held in AlBaha, Saudi
Arabia, 24-25 February 2015.
ABU3QCE 2015 is a local symposium dedicated to the exchange
of research and practice focusing on enhancing quality in
computing education. Contributions cover a broad spectrum
of computing education challenges ranging from; computer
science, computer engineering, computer information
systems, computer information technology to software
engineering education. ABU3QCE aims to publish research
that combines teaching and learning experience with
theoretically founded research within the field. The
proceedings papers cover a wide range of topics such as
cultural aspects of teaching and learning, technology
enhanced teaching, and professional competencies and their
role in the curriculum and in higher education.
The symposium is a collaborative initiative of AlBaha
University, Saudi Arabia, and Uppsala University, Sweden.
It is our hope that this symposium will highlight current
efforts, and also be the starting point for discussions,
and inspire others to contribute to take the quality of
computing education one step further.}
}
@TechReport{ it:2015-006,
author = {Farshid Besharati and Mahdad Davari and Christian
Danheimer Furedal and Bj{\"o}rn Forsberg and Niklas
Forsmark and Henrik Grandin and Jimmy Gunnarsson and Engla
Ling and Marcus Lofvars and Sven Lundgren and Luis Mauricio
and Erik Norgren and Magnus Norgren and Johan Risch and
Christos Sakalis and Stefanos Kaxiras},
title = {The {EVI} Distributed Shared Memory System},
institution = it,
department = docs,
year = 2015,
number = {2015-006},
month = feb,
abstract = {With the data handled by companies and research institutes
getting larger and larger every day, there is a clear need
for faster computing. At the same time, we have reached the
limit of power consumption and more power efficient
computing is also called for, both in the datacenter and in
the supercomputer room. For that, there is a great push,
both in industry and academia, towards increasing the
amount of computing power per watt consumed.
With this shift towards a different computing paradigm,
many older ideas are looked upon in a new light. One of
these is the distributed shared memory (DSM) systems. It is
becoming harder and harder to achieve higher performance
and better power efficiency at the same form factor as we
have always had. Furthermore, while we have seen a stop in
the constant increase of processor speeds, there is a
constant increase in network communication speeds. Software
implemented DSM is again a viable solution for high
performance computing, without the need for sacrificing
ease of programming for performance gains.
The goal of this course was to develop such a system, and
learn in the process. We chose to work with the Adapteva
Parallella boards and design a DSM system there. Over one
semester we designed and developed that system.}
}
@TechReport{ it:2015-005,
author = {Carlo Garoni and Carla Manni and Stefano Serra-Capizzano
and Debora Sesana and Hendrik Speleers},
title = {Spectral Analysis and Spectral Symbol of Matrices in
Isogeometric {G}alerkin Methods},
institution = it,
department = tdb,
year = 2015,
number = {2015-005},
month = jan,
abstract = {A linear full elliptic second order Partial Differential
Equation (PDE), defined on a $d$-dimensional domain
$\Omega$, is approximated by the isogeometric Galerkin
method based on uniform tensor-product B-splines of degrees
$(p_1,\ldots,p_d)$. The considered approximation process
leads to a $d$-level stiffness matrix, banded in a
multilevel sense. This matrix is close to a $d$-level
Toeplitz structure when the PDE coefficients are constant
and the physical domain $\Omega$ is just the hypercube
$(0,1)^d$ without using any geometry map. In such a
simplified case, a detailed spectral analysis of the
stiffness matrices has been carried out in a previous work.
In this paper, we complete the picture by considering
non-constant PDE coefficients and an arbitrary domain
$\Omega$, parameterized with a non-trivial geometry map. We
compute and study the spectral symbol of the related
stiffness matrices. This symbol describes the asymptotic
eigenvalue distribution when the fineness parameters tend
to zero (so that the matrix-size tends to infinity). The
mathematical technique used for computing the symbol is
based on the theory of Generalized Locally Toeplitz (GLT)
sequences.}
}
@TechReport{ it:2015-004,
author = {Sofia Cassel and Falk Howar and Bengt Jonsson and Bernhard
Steffen},
title = {Learning Extended Finite State Machines (extended
version)},
institution = it,
department = docs,
year = 2015,
number = {2015-004},
month = feb,
note = {Updated and superceded by Technical Report 2015-032.},
abstract = {We present a black-box active learning algorithm for
inferring extended finite state machines (EFSM)s, combining
data flow and control behavior. Different dialects of EFSMs
are widely used in tools for model-based software
development, verification, and testing. Our algorithm
infers a class of EFSMs called \emph{register automata}.
Register automata have a finite control structure, extended
with variables (registers), assignments, and guards. Our
algorithm is parameterized on a particular theory, i.e., a
set of operations and tests on the data domain that can be
used in guards.
Key to our learning technique is a novel learning model
based on so-called \emph{tree queries}. The learning
algorithm uses the tree queries to infer symbolic data
constraints on parameters, e.g., sequence numbers, time
stamps, identifiers, or even simple arithmetic. We describe
sufficient conditions for the properties that the symbolic
constraints provided by a tree query in general must have
to be usable in our learning model. We also show that,
under these conditions, our framework induces a
generalization of the classical Nerode equivalence and
canonical automata construction to the symbolic setting. We
have evaluated our algorithm in a black-box scenario, where
tree queries are realized through (black-box) testing. Our
case studies include connection establishment in TCP and a
priority queue from the Java Class Library.}
}
@TechReport{ it:2015-003,
author = {Ali Dorostkar and Maya Neytcheva and Bj{\"o}rn Lund},
title = {On Some Block-Preconditioners for Saddle Point Systems and
their {CPU-GPU} Performance},
institution = it,
department = tdb,
year = 2015,
number = {2015-003},
month = jan,
abstract = {In this work we emphasize some aspects of the numerical
and computational performance of block preconditioners for
systems with matrices of saddle point form. We discuss the
quality of a sparse approximation of the related Schur
complement for constructing an efficient preconditioner and
the achieved numerical efficiency in terms of number of
iterations. We also present a performance study of the
computational efficiency of the corresponding
preconditioned iterative solution methods, implemented
using publicly available numerical linear algebra software
packages, both on multicore CPU and GPU devices. We show
that the presently available GPU accelerators can be very
efficiently used in computer simulations involving
inner-outer solution methods and hierarchical data
structures. The benchmark problem originates from a
geophysical application, namely, the elastic Glacial
Isostatic Adjustment model, discretized using the finite
element method.}
}
@TechReport{ it:2015-002,
author = {Marco Donatelli and Mariarosa Mazza and Stefano
Serra-Capizzano},
title = {Spectral Analysis and Structure Preserving Preconditioners
for Fractional Diffusion Equations},
institution = it,
department = tdb,
year = 2015,
number = {2015-002},
month = jan,
abstract = {Fractional partial order diffusion equations are a
generalization of classical partial differential equations,
used to model anomalous diffusion phenomena. When using the
implicit Euler formula and the shifted Gr{\"u}nwald
formula, it has been shown that the related discretizations
lead to a linear system whose coefficient matrix has a
Toeplitz-like structure. In this paper we focus our
attention on the case of variable diffusion coefficients.
Under appropriate conditions, we show that the sequence of
the coefficient matrices belongs to the Generalized Locally
Toeplitz class and we compute the symbol describing its
asymptotic eigenvalue distribution, as the matrix size
diverges. We employ the spectral information for analyzing
known methods of preconditioned Krylov and multigrid type,
with both positive and negative results and with a look
forward to the multidimensional setting. We also propose
two new tridiagonal structure preserving preconditioners to
solve the resulting linear system, with Krylov methods such
as CGNR and GMRES. A number of numerical examples shows
that our proposal is more effective than recently used
circulant preconditioner.}
}
@TechReport{ it:2015-001,
author = {Victor Shcherbakov and Elisabeth Larsson},
title = {Radial Basis Function Partition of Unity Methods for
Pricing Vanilla Basket Options},
institution = it,
department = tdb,
year = 2015,
number = {2015-001},
month = jan,
abstract = {Mesh-free methods based on radial basis function (RBF)
approximation are widely used for solving PDE problems.
They are flexible with respect to the problem geometry and
highly accurate. A disadvantage of these methods is that
the linear system to be solved becomes dense for globally
supported RBFs. A remedy is to introduce localisation
techniques such as partition of unity (PU). RBF-PU methods
allow for significant sparsification of the linear system
and lower the computational effort. In this work we apply a
global RBF method as well as an RBF-PU method to problems
in option pricing. We consider one- and two-dimensional
vanilla options. In order to price American options we
employ a penalty approach. The RBF-PU method is competitive
with already existing methods and the results are promising
for extension to higher-dimensional problems.}
}
@TechReport{ it:2014-024,
author = {Stefano Serra-Capizzano},
title = {{T}oeplitz Matrices: Spectral Properties and
Preconditioning in the {CG} Method},
institution = it,
department = tdb,
year = 2014,
number = {2014-024},
month = dec,
abstract = {We consider multilevel Toeplitz matrices $T_n(f)$
generated by Lebes\-gue integrable functions $f$ defined
over $I^d$, $I=[-\pi,\pi)$, $d\ge 1$. We are interested in
the solution of linear systems with coefficient matrix
$T_n(f)$ when the size of $T_n(f)$ is large. Therefore the
use of iterative methods is recommended for computational
and numerical stability reasons. In this note we focus our
attention on the (preconditioned) conjugate gradient (P)CG
method and on the case where the symbol $f$ is known and
univariate ($d=1$): the second section treat spectral
properties of Toeplitz matrices $T_n(f)$; the third deals
with the spectral behavior of $T_n^{-1}(g) T_n(f)$ and the
fourth with the band Toeplitz preconditioning; in the fifth
section we consider the matrix algebra preconditioning
through the Korovkin theory. Then in the sixth section we
study the multilevel case $d>1$ by emphasizing the results
that have a plain generalization (those in the Sections 2,
3, and 4) and the results which strongly depend on the
number $d$ of levels (those in Section 5): in particular
the quality of the matrix algebra preconditioners
(circulants, trigonometric algebras, Hartley etc.)
deteriorates sensibly as $d$ increases.
A section of conclusive remarks and two appendices treating
the theory of the (P)CG method and spectral distributional
results of structured matrix sequences.}
}
@TechReport{ it:2014-023,
author = {Venkatraman Iyer and Frederik Hermans and Thiemo Voigt},
title = {Detecting and Avoiding Multiple Sources of Interference in
the 2.4 {GHz} Spectrum},
institution = it,
department = docs,
year = 2014,
number = {2014-023},
month = dec,
abstract = {Sensor networks operating in the 2.4 GHz band often face
cross-technology interference from co-located WiFi and
Bluetooth devices. To enable effective interference
mitigation, a sensor network needs to know the type of
interference it is exposed to. However, existing approaches
to interference detection are not able to handle multiple
concurrent sources of interference. In this paper, we
address the problem of identifying multiple channel
activities impairing a sensor network~s communication, such
as simultaneous WiFi traffic and Bluetooth data transfers.
We present SpeckSense, an interference detector that
distinguishes between different types of interference using
a unsupervised learning technique. Additionally, SpeckSense
features a classifier that distinguishes between moderate
and heavy channel traffic, and also identifies WiFi
beacons. In doing so, it facilitates interference avoidance
through channel blacklisting. We evaluate SpeckSense on
common mote hardware and show how it classifies concurrent
interference under real-world settings. We also show how
SpeckSense improves the performance of an existing
multichannel data collection protocol by 30\%.}
}
@TechReport{ it:2014-022,
author = {Carlo Garoni and Stefano Serra-Capizzano and Paris
Vassalos},
title = {Tools for Determining the Asymptotic Spectral Distribution
of {H}ermitian Matrix-Sequences and Applications},
institution = it,
department = tdb,
year = 2014,
number = {2014-022},
month = dec,
abstract = {We consider sequences of Hermitian matrices with
increasing dimension, and we provide a general tool for
deducing the asymptotic spectral distribution of a
`difficult' sequence $\{A_n\}_n$, starting from the one of
`simpler' sequences $\{B_{n,m}\}_n$ that approximate
$\{A_n\}_n$ when $m\to\infty$. The tool is based on the
notion of approximating class of sequences (a.c.s.), which
was inspired by the work of Paolo Tilli and the second
author, and is applied here in a more general setting. An
a.c.s.-based proof of the famous Szego theorem on the
spectral distribution of Toeplitz matrices is finally presented.}
}
@TechReport{ it:2014-021,
author = {Carlo Garoni and Stefano Serra-Capizzano and Debora
Sesana},
title = {Spectral Analysis and Spectral Symbol of $d$-variate
$\mathbb{Q}_p$ {L}agrangian {FEM} Stiffness Matrices},
institution = it,
department = tdb,
year = 2014,
number = {2014-021},
month = nov,
abstract = {We study the spectral properties of the stiffness matrices
coming from the $\mathbb{Q}_p$ Lagrangian FEM approximation
of $d$-dimensional second order elliptic differential
problems; here, $p=(p_1,\ldots,p_d)\in\mathbb{N}^d$ and
$p_j$ represents the polynomial approximation degree in the
$j$-th direction. After presenting a construction of these
matrices, we investigate the conditioning (behavior of the
extremal eigenvalues and singular values) and the
asymptotic spectral distribution in the Weyl sense, and we
find out the so-called (spectral) symbol describing the
asymptotic spectrum.
We also study the properties of the symbol, which turns out
to be a $d$-variate function taking values in the space of
$D(p)\times D(p)$ Hermitian matrices, where
$D(p)=\prod_{j=1}^d p_j$. Unlike the stiffness matrices
coming from the $p$\,-degree B-spline IgA approximation of
the same differential problems, where a unique $d$-variate
real-valued function describes all the spectrum, here the
spectrum is described by $D(p)$ different functions, that
is the $D(p)$ eigenvalues of the symbol, which are
well-separated, far away, and exponentially diverging with
respect to $p$ and $d$. This very involved picture provides
a clean explanation of: a) the difficulties encountered in
designing robust solvers, with convergence speed
independent of the matrix size, of the approximation
parameters $p$, and of the dimensionality $d$; b) the
possible convergence deterioration of known iterative
methods, already for moderate $p$ and $d$.}
}
@TechReport{ it:2014-020,
author = {Magnus Grandin and Sverker Holmgren},
title = {Parallel Data Structures and Algorithms for
High-Dimensional Structured Adaptive Mesh Refinement},
institution = it,
department = tdb,
year = 2014,
number = {2014-020},
month = oct,
abstract = {Numerical solution of high-dimensional partial
differential equations often results in challenging
computations. Using a uniform discretization of the spatial
domain quickly becomes untractable due to the exponential
increase in problem size with dimensionality. However, by
employing a spatially adaptive discretization scheme the
number of grid points can often be reduced significantly.
In this note we describe a parallel version of an earlier
presented adaptive scheme which generates the mesh by
recursive bisection, allowing mesh blocks to be arbitrarily
anisotropic to allow for fine structures in some directions
without over-refining in other directions. We extend the
serial framework by presenting parallel algorithms for
organizing the mesh blocks in a distributed kd-tree and the
necessary operations for implementing structured adaptive
mesh refinement on a parallel computer system.}
}
@TechReport{ it:2014-019,
author = {Magnus Grandin},
title = {Data Structures and Algorithms for High-Dimensional
Structured Adaptive Mesh Refinement},
institution = it,
department = tdb,
year = 2014,
number = {2014-019},
month = oct,
abstract = {Spatial discretization of high-dimensional partial
differential equations requires data representations that
are of low overhead in terms of memory and complexity.
Uniform discretization of computational domains quickly
grows out of reach due to an exponential increase in
problem size with dimensionality. Even with spatial
adaptivity, the number of mesh data points can be
unnecesarily large if care is not taken as to where
refinement is done. We propose an adaptive scheme that
generates the mesh by recursive bisection, allowing mesh
blocks to be arbitrarily anisotropic to allow for fine
structures in some directions without over-refining in
those directions that suffice with less refinement. We
describe in detail how the mesh blocks are organized in a
kd-tree and the algorithms that update the mesh as is
necessary for preserved accuracy in the solution.
Algorithms for refinement, coarsening and 2:1 balancing of
a mesh hierarchy are derived, and we describe how
information is retrieved from the tree structure by means
of binary search. To show the capabilities of our
framework, we present results showing examples of generated
meshes and evaluate the algorithmic scalability on a suite
of test problems. In summary, we conclude that although the
worst-case complexity of sorting the nodes and building the
node map index is $n^2$, the average runtime scaling in our
examples is no worse than $n \log n$.}
}
@TechReport{ it:2014-018,
author = {Olov Ros{\'e}n and Alexander Medvedev},
title = {Parallelization of the Particle Filter via Series
Expansions},
institution = it,
department = syscon,
year = 2014,
number = {2014-018},
month = aug,
abstract = {Parallelizability of an algorithm is nowadays a highly
desirable property as computer hardware is becoming
increasingly parallel. In this paper, a formulation of the
particle filtering algorithm, suitable for parallel or
distributed computing, is proposed. From the particle set,
a series expansion is fitted to the posterior probability
density function. The global information expressed by the
particles can in this way be compressed to a few
informative coefficients that can be efficiently
communicated between the local processing units.
Experiments on a shared-memory multicore processor using up
to 8 cores show that linear speedup in the number of used
cores is achieved.}
}
@TechReport{ it:2014-017,
author = {David R. Cok and Aaron Stump and Tjark Weber},
title = {The 2013 {SMT} Evaluation},
institution = it,
department = csd,
year = 2014,
number = {2014-017},
month = jul,
abstract = {After 8 years of SMT Competitions, the SMT Steering
Committee decided, for 2013, to sponsor an evaluation of
the status of SMT benchmarks and solvers, rather than
another competition. This report summarizes the results of
the evaluation, conducted by the authors. The key
observations are that (1) the competition results are quite
sensitive to randomness and (2) the most significant need
for the future is assessment and improvement of benchmarks
in the light of SMT applications. The evaluation also
measured competitiveness of solvers, general coverage of
solvers, logics, and benchmarks, and degree of
repeatability of measurements and competitions.}
}
@TechReport{ it:2014-016,
author = {Torbj{\"o}rn Wigren},
title = {Identifiability and Limit Cycles},
institution = it,
department = syscon,
year = 2014,
number = {2014-016},
month = may,
abstract = {The report discusses when the non-linear dynamic equations
of a non-linear system in a limit-cycle can be determined
from measured data. The minimal order needed for this turns
out to be the minimal dimension in which the stable orbit
of the system does not intersect itself. This is
illustrated with a fourth order spiking neuron model, which
is identified using a non-linear second order differential
equation model.}
}
@TechReport{ it:2014-015,
author = {Sven-Olof Nystr{\"o}m},
title = {Subtyping, consistency and derivability},
institution = it,
department = csd,
year = 2014,
number = {2014-015},
month = may,
abstract = {Earlier work on subtyping has focused on the problem of
constructing a typing for a given program. This paper
considers a slightly different problem: Given a lambda
term, is the corresponding constraint system
\emph{consistent}? An $O(n^3)$ algorithm for checking the
consistency of constraint systems is presented, where $n$
is the size of the constraint system.
The paper also considers the problem of
\emph{derivability}, i.e., whether a property can be
derived from the corresponding constraint system and gives
an $O(n^3)$ algorithm for checking derivability of a class
of constraints.}
}
@TechReport{ it:2014-014,
author = {Torbj{\"o}rn Wigren},
title = {{MATLAB} Software for Identification of Nonlinear
Autonomous Systems - Revision 1},
institution = it,
department = syscon,
year = 2014,
number = {2014-014},
month = apr,
note = {The software package can be downloaded from
\url{http://www.it.uu.se/research/publications/reports/2014-014/SWAutonomous.zip}.}
,
abstract = {This report is intended as a user~s manual for a package
of MATLAB scripts and functions, developed for recursive
and batch identification of nonlinear autonomous state
space models of order 2. The core of the package consists
of implementations of four algorithms for this purpose.
There are two least squares batch schemes and two recursive
algorithms based on Kalman filtering techniques.
The algorithms are based on a continuous time, structured
black box state space model of a nonlinear autonomous
system of order 2. The software can only be run off-line,
i.e. no true real time operation is possible. The recursive
algorithms are however implemented so that true on-line
operation can be obtained by extraction of the main
algorithmic loops. The user must then provide the real time
environment. The software package contains scripts and
functions that allow the user to either input live
measurements or to generate test data by simulation. The
functionality for display of results include scripts for
plotting of data and parameters. The estimated model
obtained at the end of a run can be simulated and the model
output plotted, alone or together with the data used for
identification.}
}
@TechReport{ it:2014-013,
author = {Thomas Lind and {\AA}sa Cajander and Bengt Sandblad},
title = {Inf{\"o}randet av {R}aindance Bokf{\"o}ringsportal vid
Uppsala universitet - En kortfattad rapport fr{\aa}n
{KiA}-projektet},
institution = it,
department = vi2,
year = 2014,
number = {2014-013},
month = apr,
note = {In Swedish.},
abstract = {Under senv{\aa}ren och h{\"o}sten 2013 genomf{\"o}rdes en
studie f{\"o}r att dra l{\"a}rdomar av inf{\"o}randet som
skedde inf{\"o}r {\aa}rsskiftet 2012-2013 utav
Bokf{\"o}ringsportalen, en del av ekonomisystemet Raindance
vid Uppsala universitet. Ut{\"o}ver Bokf{\"o}ringsportalen
har studien {\"a}ven ber{\"o}rt fr{\aa}gor om inf{\"o}rande
av IT kopplat till avdelningen f{\"o}r ekonomi och
upphandling mer generellt.
Studien har utf{\"o}rts inom ramen f{\"o}r KiA-projektet
och baseras p{\aa} fyra intervjuer med personal vid
universitetsf{\"o}rvaltningens avdelning f{\"o}r ekonomi
och upphandling samt sex intervjuer med
ekonomiadministrat{\"o}rer fr{\aa}n olika institutioner vid
universitetet.
Intervjuerna visar p{\aa} ett brett spektra av
uppfattningar och inst{\"a}llningar till inf{\"o}randet av
Bokf{\"o}ringsportalen, d{\"a}r vissa anser att hela deras
arbetssituation har f{\"o}r{\"a}ndrats medan andra ser
f{\"o}r{\"a}ndringen som knappt m{\"a}rkbar. Synen p{\aa}
f{\"o}r{\"a}ndringen som positiv eller negativ varierar
ocks{\aa} bland respondenterna. Vitt skilda
f{\"o}rh{\aa}llanden i organisationen av
ekonomiadministrat{\"o}rernas roller och arbetsuppgifter,
samt faktorer r{\"o}rande institutionerna i {\"o}vrigt,
bidrar till att skapa v{\"a}ldigt olika
f{\"o}ruts{\"a}ttningar vid f{\"o}r{\"a}ndring av IT som
p{\aa}verkar administrat{\"o}rernas arbetsmilj{\"o}.}
}
@TechReport{ it:2014-012,
author = {Per L{\"o}tstedt and Lina Meinecke},
title = {Simulation of Stochastic Diffusion via First Exit Times},
institution = it,
department = tdb,
year = 2014,
number = {2014-012},
month = apr,
abstract = {In molecular biology it is of interest to simulate
diffusion stochastically. In the mesoscopic model we
partition a biological cell into voxels in an unstructured
mesh. In each voxel the number of molecules is recorded at
each time step and molecules can jump between neighboring
voxels to model diffusion. The jump rates are computed by
discretizing the diffusion equation on the unstructured
mesh. If the mesh is of poor quality, due to a complicated
cell geometry, standard discretization methods can generate
negative jump coefficients, which no longer allows the
interpretation as the probability to leave the subvolume.
We propose a method based on the mean first exit time of a
molecule from a subvolume, which guarantees positive jump
coefficients. Two approaches to exit times, a global and a
local one, are presented and tested in simulations with
diffusion and chemical reactions on meshes of different
quality in two dimensions.}
}
@TechReport{ it:2014-011,
author = {Martin Tillenius and Elisabeth Larsson and Erik Lehto and
Natasha Flyer},
title = {A Task Parallel Implementation of an {RBF}-generated
Finite Difference Method for the Shallow Water Equations on
the Sphere},
institution = it,
department = tdb,
year = 2014,
number = {2014-011},
month = apr,
abstract = {Radial basis function-generated finite difference (RBF-FD)
methods have recently been proposed as very interesting for
global scale geophysical simulations, and have been shown
to outperform established pseudo-spectral and discontinuous
Galerkin methods for shallow water test problems. In order
to be competitive for very large scale simulations, the
implementation of the RBF-FD methods needs to be efficient
and adapted for modern multicore based computer
architectures. The main computational operations in the
method consist of unstructured sparse matrix-vector
multiplications, which are in general not well suited for
multicore-based computers. In this work, the method is
implemented for clusters of multicore computers using a
task-based parallel programming model. Performance
experiments showed that our implementation achieves 71\% of
theoretical speedup within one computational node, and
90~100\% of linear speedup between nodes. A speedup of 178
times compared with the original MATLAB implementation was
achieved for a global shallow water problem with a 30km
resolution. }
}
@TechReport{ it:2014-010,
author = {Martin Tillenius},
title = {{SuperGlue}: A Shared Memory Framework using
Data-Versioning for Dependency-Aware Task-Based
Parallelization},
institution = it,
department = tdb,
year = 2014,
number = {2014-010},
month = apr,
abstract = {In computational science, making efficient use of modern
multicore based computer hardware is necessary in order to
deal with complex real-life application problems. However,
with increased hardware complexity, the cost in man hours
of writing and re-writing software to adapt to evolving
computer systems is becoming prohibitive. Task based
parallel programming models aim to allow the application
programmers to focus on the algorithms and applications,
while the performance is handled by a runtime system that
schedules the tasks onto nodes, cores, and accelerators. In
this paper we describe a task parallel programming model
where dependencies are represented through data versioning.
The benefits of using this type of model are that it is
easy to represent different types of dependencies and that
scheduling decisions can be made locally. We implement this
as a freely available C++ header-only template library, and
show experimental results indicating that our
implementation scales well, and performs well in comparison
to other related efforts.}
}
@TechReport{ it:2014-009,
author = {Torbj{\"o}rn Wigren},
title = {On a Limitation in Networked Flow Control},
institution = it,
department = syscon,
year = 2014,
number = {2014-009},
month = mar,
abstract = {The paper analyzes a continuous time flow control system,
with flow of a general quantity from a source node to a
sink node. The flow is one-directional, meaning that there
is a saturation between the nodes that limits the flow to
be positive and below a maximum. The controlled plant is
located in the sink node and the controller is located in
the source node. The plant and the controller are modeled
by linear filters parameterized with poles and zeros. Feed
forward control from measured disturbances is included.
Delays affect both the downlink control signal and the
uplink measurement signals. The paper proves that for large
delays, $L_2$-stability does not follow from the Popov
criterion unless the quotient of the products of all zeros
and the product of all poles is less than $1/kG_p$, where
$k$ is the slope of the saturation and $G_p$ is the gain
constant of the loop gain. In case the plant models a leaky
reservoir, the conclusion is that the amount of low
frequency gain of the controller cannot be arbitrarily high
at the same time as the amount of leakage of the reservoir
is arbitrarily low. In communications this means that an
increased requirement to regulate static errors of the
reservoir needs to be accompanied by a reduced flow
capacity.}
}
@TechReport{ it:2014-008,
author = {Torsten S{\"o}derstr{\"o}m and Roberto Diversi and Umberto
Soverini},
title = {A Generalized Instrumental Variable Framework for {EIV}
Identification Methods when the Measurement Noises are
Mutually Correlated},
institution = it,
department = syscon,
year = 2014,
number = {2014-008},
month = mar,
abstract = {In this paper, the previously introduced Generalized
Instrumental Variable Estimator (GIVE) is extended to the
case of errors-in-variables models where the additive input
and output noises are mutually correlated white processes.
It is shown how many estimators proposed in the literature
can be described as various special cases of a generalized
instrumental variable framework. It is also investigated
how to analyze the common situation where some of the
equations that define the estimator are to hold exactly,
and others to hold approximately in a least squares sense,
providing a detailed study of the accuracy analysis.}
}
@TechReport{ it:2014-007,
author = {Ali Dorostkar and Dimitar Lukarski and Bj{\"o}rn Lund and
Maya Neytcheva and Yvan Notay and Peter Schmidt},
title = {Parallel Performance Study of Block-Preconditioned
Iterative Methods on Multicore Computer Systems},
institution = it,
department = tdb,
year = 2014,
number = {2014-007},
month = mar,
abstract = {In this work we benchmark the performance of a
preconditioned iterative method, used in large scale
computer simulations of a geophysical application, namely,
the elastic Glacial Isostatic Adjustment model. The model
is discretized using the finite element method. It gives
raise to algebraic systems of equations with matrices that
are large, sparse, nonsymmetric, indefinite and with a
saddle point structure. The efficiency of solving systems
of the latter type is crucial as it is to be embedded in a
time-evolution procedure, where systems with matrices of
similar type have to be solved repeatedly many times.
The computer code for the simulations is implemented using
available open source software packages - Deal.ii,
Trilinos, PARALUTION and AGMG. These packages provide
toolboxes with state-of-art implementations of iterative
solution methods and preconditioners for multicore computer
platforms and GPU. We present performance results in terms
of numerical and computational efficiency, number of
iterations and execution time, and compare the timing
results against a sparse direct solver from a commercial
finite element package, that is often used by applied
scientists in their simulations.}
}
@TechReport{ it:2014-006,
author = {H{\"o}{\"o}k, Lars Josef},
title = {On the Bimodality in an Introductory Programming Course:
an Analysis of Student Performance Factors},
institution = it,
department = tdb,
year = 2014,
number = {2014-006},
month = mar,
abstract = {In this work, the student performance in an introductory
programming course given at the department of information
technology at Uppsala University is analyzed. The results
from the final exam are studied and the potential
bimodality of the distribution is investigated. A
questionnaire, answered by the students at the final exam
is analyzed, including study behavior and potential
connections to the performance at the final exam.}
}
@TechReport{ it:2014-005,
author = {Andreas Sandberg and Erik Hagersten and David
Black-Schaffer},
title = {Full Speed Ahead: Detailed Architectural Simulation at
Near-Native Speed},
institution = it,
department = docs,
year = 2014,
number = {2014-005},
month = mar,
abstract = {Popular microarchitecture simulators are typically several
orders of magnitude slower than the systems they simulate.
This leads to two problems: First, due to the slow
simulation rate, simulation studies are usually limited to
the first few billion instructions, which corresponds to
less than 10\% the execution time of many standard
benchmarks. Since such studies only cover a small fraction
of the applications, they run the risk of reporting
unrepresentative application behavior unless sampling
strategies are employed. Second, the high overhead of
traditional simulators make them unsuitable for
hardware/software co-design studies where rapid turn-around
is required.
In spite of previous efforts to parallelize simulators,
most commonly used full-system simulations remain single
threaded. In this paper, we explore a simple and effective
way to parallelize sampling full-system simulators. In
order to simulate at high speed, we need to be able to
efficiently fast-forward between sample points. We
demonstrate how hardware virtualization can be used to
implement highly efficient fast-forwarding in the standard
gem5 simulator and how this enables efficient execution
between sample points. This extremely rapid fast-forwarding
enables us to reach new sample points much quicker than a
single sample can be simulated. Together with efficient
copying of simulator state, this enables parallel execution
of sample simulation. These techniques allow us to
implement a highly scalable sampling simulator that
exploits sample-level parallelism.
We demonstrate how virtualization can be used to
fast-forward simulators at 90\% of native execution speed
on average. Using virtualized fast-forwarding, we
demonstrate a parallel sampling simulator that can be used
to accurately estimate the IPC of standard workloads with
an average error of 2.2\% while still reaching an execution
rate of 2.0 GIPS (63\% of native) on average. We
demonstrate that our parallelization strategy scales almost
linearly and simulates one core at up to 93\% of its native
execution rate, 19,000x faster than detailed simulation,
while using 8 cores.}
}
@TechReport{ it:2014-004,
author = {Emil Kieri},
title = {Stiff Convergence of Force-Gradient Operator Splitting
Methods},
institution = it,
department = tdb,
year = 2014,
number = {2014-004},
month = feb,
abstract = {We consider force-gradient, also called modified
potential, operator splitting methods for problems with
unbounded operators. We prove that force-gradient operator
splitting schemes retain their classical orders of accuracy
for time-dependent partial differential equations of
parabolic or Schr{\"o}dinger type, provided that the
solution is sufficiently regular.}
}
@TechReport{ it:2014-003,
author = {{\AA}sa Cajander and Thomas Lind and Gerolf Nauwerck and
Britta Nyberg and Bengt Sandblad},
title = {Ekonomiadministrat{\"o}rernas {IT}-relaterade
arbetsmilj{\"o} vid {U}ppsala universitet - En kortfattad
rapport fr{\aa}n {KIA}-projektet},
institution = it,
department = vi2,
year = 2014,
number = {2014-003},
month = feb,
note = {In Swedish.},
abstract = { Denna rapport inneh{\aa}ller en kartl{\"a}ggning av
ekonomiadministrat{\"o}rers, ekonomiassistenters och
ekonomiadministrat{\"o}rers digitala arbetsmilj{\"o} p{\aa}
Uppsala universitet. Rapporten {\"a}r skriven med
utg{\aa}ngspunkt fr{\aa}n att l{\"a}saren har inblick i hur
ekonomiassistenterekonomiadministrat{\"o}rer arbetar idag
p{\aa} Uppsala universitet, samt har kunskap kring de olika
IT-system som anv{\"a}nds. Kartl{\"a}ggningen gjordes under
h{\"o}sten 2013 d{\aa} 12 ekonomiassistenter
ekonomiadministrat{\"o}rer bes{\"o}ktes under 2-3 timmar
och metoden Contextual Inquiry anv{\"a}ndes. Inledningsvis
f{\"o}rklaras begreppen arbetsmilj{\"o} och IT, och Robert
Karaseks modell med dimensionerna krav kontroll och
st{\"o}d presenteras. Dessa dimensioner ligger sedan till
grund f{\"o}r kartl{\"a}ggningen som kortfattat presenterar
de problem som har identifierats kopplat till den digitala
arbetsmilj{\"o}n. N{\aa}gra av de problem som identifierats
i kartl{\"a}ggningen {\"a}r avsaknaden av {\"o}verblick,
st{\"a}ndiga avbrott, och fragmenterad information.
Rapporten avslutas med en lista med rekommendationer p{\aa} f{\"o}rb{\"a}ttringar.}
}
@TechReport{ it:2014-002,
author = {Peter Hellstr{\"o}m},
title = {Problems in the Integration of Timetabling and Train
Traffic Control},
institution = it,
department = vi2,
year = 2014,
number = {2014-002},
month = jan
}
@TechReport{ it:2014-001,
author = {Martin Tillenius and Elisabeth Larsson and Rosa M. Badia
and Xavier Martorell},
title = {Resource-Aware Task Scheduling},
institution = it,
department = tdb,
year = 2014,
number = {2014-001},
month = jan,
abstract = {Dependency-aware task-based parallel programming models
have proven to be successful for developing efficient
application software for multicore-based computer
architectures. The programming model is amenable to
programmers, thereby supporting productivity, while
hardware performance is achieved through a run-time system
that dynamically schedules tasks onto cores in such a way
that all dependencies are respected. However, even if the
scheduling is completely successful with respect to load
balancing, the scaling with the number of cores may be
sub-optimal due to resource contention. Here we consider
the problem of scheduling tasks not only with respect to
their inter-dependencies, but also with respect to their
usage of resources such as memory and bandwidth. At the
software level, this is achieved by user annotations of the
task resource consumption. In the run-time system, the
annotations are translated into scheduling constraints.
Experimental results for different hardware, demonstrating
performance gains both for model examples and real
applications are presented. Furthermore, we provide a set
of tools to detect resource sensitivity and predict the
performance improvements that can be achieved by
resource-aware scheduling. These tools are solely based on
parallel execution traces and require no instrumentation or
modification of the application code.}
}
@TechReport{ it:2013-027,
author = {Bengt Sandblad},
title = {Checklista f{\"o}r god arbetsmilj{\"o} vid datorst{\"o}tt
arbete},
institution = it,
department = vi2,
year = 2013,
number = {2013-027},
month = dec,
note = {In Swedish.},
abstract = {Redan idag sk{\"o}ts det mesta av allt arbete inom
administrativt arbete, {\"a}rendehantering m.m. med
hj{\"a}lp av datorer. Att arbetet {\"a}r datorst{\"o}tt
inneb{\"a}r givetvis inte att de professionella som ska
utf{\"o}ra det direkta arbetet har som huvuduppgift att
hantera en dator. De ska kunna utf{\"o}ra sitt arbete
p{\aa} ett effektivt s{\"a}tt och ha en s{\aa} bra
arbetssituation som m{\"o}jligt. Sj{\"a}lvfallet ska
ocks{\aa} arbetet pr{\"a}glas av en god arbetsmilj{\"o}.
Det h{\"a}r dokumentet beskriver hur man kan utv{\"a}rdera
arbetsmilj{\"o}- och h{\"a}lsoaspekter i syfte att
f{\"o}rebygga eller {\aa}tg{\"a}rda olika slags
arbetsmilj{\"o}problem. Inneh{\aa}llet utg{\aa}r i
m{\aa}ngt och mycket fr{\aa}n att arbetet utf{\"o}rs med
hj{\"a}lp av IT-st{\"o}d, men en hel del {\"a}r relevant
{\"a}ven f{\"o}r arbeten som inte i huvudsak st{\"o}ds av
IT. Basen i utv{\"a}rderingen {\"a}r en checklista som
finns i slutet av dokumentet. Checklistan kan anv{\"a}ndas
f{\"o}r att utv{\"a}rdera befintliga arbeten, men den kan
ocks{\aa} anv{\"a}ndas i f{\"o}rebyggande syfte. }
}
@TechReport{ it:2013-026,
author = {Sofia Cassel and Falk Howar and Bengt Jonsson and Maik
Merten and Bernhard Steffen},
title = {A Succinct Canonical Register Automaton Model},
institution = it,
department = docs,
year = 2013,
number = {2013-026},
month = dec,
note = {This is an extended version of a paper published in ATVA
2011. The extended version has been accepted for
publication in JLAP.},
abstract = {We present a novel canonical automaton model, based on
register automata, that can be used to specify protocol or
program behavior. Register automata have a finite control
structure and a finite number of registers (variables), and
process sequences of terms that carry data values from an
infinite domain. We consider register automata that compare
data values for equality. A major contribution is the
definition of a canonical automaton representation of any
language recognizable by a deterministic register
automaton, by means of a Nerode congruence. This canonical
form is well suited for modeling, e.g., protocols or
program behavior. Our model can be exponentially more
succinct than previous proposals, since it filters out
'accidental' relations between data values. This opens the
way to new practical applications, e.g., in automata
learning.}
}
@TechReport{ it:2013-025,
author = {Jonatan Lind{\'e}n and Bengt Jonsson},
title = {A Skiplist-Based Concurrent Priority Queue with Minimal
Memory Contention},
institution = it,
department = docs,
year = 2013,
number = {2013-025},
month = dec,
note = {Updated by Technical Report 2018-003, February 2018. See
\url{http://www.it.uu.se/research/publications/reports/2018-003}.}
,
abstract = {Priority queues are fundamental to many multiprocessor
applications. Several priority queue algorithms based on
skiplists have been proposed, as skiplists allow concurrent
accesses to different parts of the data structure in a
simple way. However, for priority queues on
multiprocessors, an inherent bottleneck is the operation
that deletes the minimal element. We present a
linearizable, lock-free, concurrent priority queue
algorithm, based on skiplists, which minimizes the
contention for shared memory that is caused by the {\sc
DeleteMin} operation. The main idea is to minimize the
number of global updates to shared memory that are
performed in one {\sc DeleteMin}. In comparison with other
skiplist-based priority queue algorithms, our algorithm
achieves a 30 -- 80\% improvement.}
}
@TechReport{ it:2013-024,
author = {Thomas Lind and Fredrik Brattl{\"o}f and {\AA}sa Cajander
and Bengt Sandblad and Bengt G{\"o}ransson and Anders
Jansson},
title = {F{\"o}rstudierapport: Inf{\"o}rande av
verksamhetsst{\"o}djande {IT}-system. Problem, effekter och
nytta},
institution = it,
department = vi2,
year = 2013,
number = {2013-024},
month = dec,
note = {In Swedish.},
abstract = {Under h{\"o}sten 2011 har en f{\"o}rstudie genomf{\"o}rts
f{\"o}r att kartl{\"a}gga och analysera dagens processer
f{\"o}r utveckling, anskaffande, inf{\"o}rande och
utv{\"a}rdering av administrativa IT-system vid Uppsala
universitet (UU). F{\"o}rstudien, Inf{\"o}rande av
verksamhetsst{\"o}djande IT-system. Problem, effekter och
nytta, har genomf{\"o}rts av forskare vid avdelningen
f{\"o}r m{\"a}nniska-datorinteraktion (MDI) vid
institutionen f{\"o}r informationsteknologi, UU.
F{\"o}rstudien har gjorts p{\aa} uppdrag av
universitetsdirekt{\"o}r Ann Fust och kontaktperson har
varit Britta Nyberg, enheten f{\"o}r planering,
uppf{\"o}ljning och st{\"o}d f{\"o}r verksamhetsutveckling.
Arbetet har dels best{\aa}tt av en kartl{\"a}ggning och
analys av dagens utvecklings- och inf{\"o}randeprocesser
och de problem man upplever i samband med dessa, dels
n{\aa}gra analyser av hur anv{\"a}ndare uppfattar de
IT-system man idag har.
Sammanfattningsvis har kartl{\"a}ggningen och analysen
visat att det finns en stor f{\"o}rb{\"a}ttringspotential
n{\"a}r det g{\"a}ller processer f{\"o}r verksamhets- och
IT-utveckling samt hur anv{\"a}ndbarhetsaspekter beaktas i
utveckling, anskaffande, inf{\"o}rande och utv{\"a}rdering
av IT-system. Kartl{\"a}ggningen av processer som
anv{\"a}nds vid UU visar att det inte finns n{\aa}gra
enhetliga processer som anv{\"a}nds generellt inom UU, men
att det lokalt finns fungerande s{\aa}dana. N{\aa}gra
exempel {\"a}r f{\"o}rvaltningen som sedan n{\aa}gra {\aa}r
arbetar enligt PM3, och avdelningen f{\"o}r IT och
ink{\"o}p som anv{\"a}nder sig av ITIL. I de idag
p{\aa}g{\aa}ende IT-projekten varierar arbetss{\"a}ttet
mycket. Det finns inga rekommenderade processer eller
arbetss{\"a}tt utan projektledaren l{\"a}gger upp arbetet
baserat p{\aa} egna erfarenheter.
Inom UU arbetar man generellt inte med
anv{\"a}ndarcentrerade processer, och
anv{\"a}ndbarhetsaspekter {\"a}r inte prioriterade. Inom
vissa projekt och i viss f{\"o}rvaltning f{\"o}rekommer en
del arbete med fokus p{\aa} anv{\"a}ndbarhet.
Referensgrupper anv{\"a}nds som en form av
anv{\"a}ndarmedverkan, men med olika m{\aa}l och syften.
Inf{\"o}randeprocesser upplevs generellt som problematiska
inom UU och h{\"a}r finns p{\aa}tagliga problem. Den
upplevda anv{\"a}ndbarheten i de administrativa IT-systemen
varierar, men generellt anser f{\"o}rstudiens
intervjupersoner att det finns stor
f{\"o}rb{\"a}ttringspotential.
Fallstudien av Raindanceportalen visar att olika
anv{\"a}ndargrupper upplever systemet p{\aa} helt olika
s{\"a}tt. De som har utbildning i Raindance
(ekonomiadministrat{\"o}rer) och anv{\"a}nder det i sina
k{\"a}rnuppgifter upplever att systemet i ganska stor
utstr{\"a}ckning st{\"o}der arbetet. {\"O}vriga
anv{\"a}ndare som anv{\"a}nder systemet mer s{\"a}llan och
som administrativt st{\"o}dsystem har klart st{\"o}rre
problem med systemet.
I en avslutande diskussion ger vi en sammanst{\"a}llning av
de observerade problemen, ger f{\"o}rslag p{\aa} vad som
fordras f{\"o}r att utveckla kunskaper kring problem och
m{\"o}jligheter och f{\"o}r att inf{\"o}ra
f{\"o}rb{\"a}ttrade processer, samt f{\"o}r att ~ p{\aa} sikt ~ f{\aa} b{\"a}ttre och effektivare administrativa IT-system inom UU.}
}
@TechReport{ it:2013-023,
author = {Ali Safdari-Vaighani and Alfa Heryudono and Elisabeth
Larsson},
title = {A Radial Basis Function Partition of Unity Collocation
Method for Convection-Diffusion Equations},
institution = it,
department = tdb,
year = 2013,
number = {2013-023},
month = nov,
abstract = {Numerical solution of multi-dimensional PDEs is a
challenging problem with respect to computational cost and
memory requirements, as well as regarding representation of
realistic geometries and adaption to solution features.
Meshfree methods such as global radial basis function
approximation have been successfully applied to several
types of problems. However, due to the dense linear systems
that need to be solved, the computational cost grows
rapidly with dimension. In this paper, we instead propose
to use a locally supported RBF collocation method based on
a partition of unity approach to numerically solve
time-dependent PDEs. We investigate the stability and
accuracy of the method for convection-diffusion problems in
two space dimensions as well as for an American option
pricing problem. The numerical experiments show that we can
achieve both spectral and high-order algebraic convergence
for convection-diffusion problems, and that we can reduce
the computational cost for the option pricing problem by
adapting the node layout to the problem characteristics. }
}
@TechReport{ it:2013-022,
author = {Lina Meinecke and Per L{\"o}tstedt},
title = {Stochastic Diffusion Processes on {C}artesian Meshes},
institution = it,
department = tdb,
year = 2013,
number = {2013-022},
month = nov,
abstract = {Diffusion of molecules is simulated stochastically by
letting them jump between voxels in a Cartesian mesh. The
jump coefficients are first derived using finite
difference, finite element, and finite volume
approximations of the Laplacian on the mesh. An alternative
is to let the first exit time for a molecule in random walk
in a voxel define the jump coefficient. Such coefficients
have the advantage of always being non-negative. These four
different ways of obtaining the diffusion propensities are
compared theoretically and in numerical experiments.}
}
@TechReport{ it:2013-021,
author = {Bengt Carlsson and Jes{\'u}s Zambrano},
title = {Fault Detection and Isolation of Sensors in Aeration
Control Systems -- the Airflow Ratio Method},
institution = it,
department = syscon,
year = 2013,
number = {2013-021},
month = oct,
abstract = {In this paper, we consider the problem of detecting sensor
faults in the aeration system of an activated sludge
process. The purpose is to detect possible faults in the
dissolved oxygen sensors. The dissolved oxygen
concentration in each aerated zone is assumed to be
automatically controlled. As the basis for a fault
detection algorithm we propose to use the ratio of air flow
rates into different zones. The method is evaluated by
using the Benchmark Simulation Model n^{o}1 (BSM1) via
Monte Carlo simulations. Results show that this method
gives a good performance in terms of correct an early fault
detection and isolation.}
}
@TechReport{ it:2013-020,
author = {Dimitar Lukarski and Tobias Skoglund},
title = {A Priori Power Estimation of Linear Solvers on Multi-Core
Processors},
institution = it,
department = tdb,
year = 2013,
number = {2013-020},
month = sep,
abstract = {High-performance computing (HPC) centres simulate complex
scientific models which provide vital understanding of our
world. In the recent years, power efficiency has become a
critical aspect in the new HPC facilities because of high
energy consumption costs. In this work, we present our
study on power consumption of linear solvers on modern
multi-core CPUs which are widely used in many scientific
applications. We focus on both dense and sparse linear
solvers - parallel direct solvers for the dense, and
parallel iterative methods for the sparse problems.
We provide answers to the questions -- what is the energy
efficiency using multi-core parallel algorithms for linear
systems and do we save energy using more cores?
Furthermore, we propose a methodology for estimating total
power consumption. Based on benchmarks which achieve high
accuracy we estimate total power usage of the whole
solution phase on multi-core CPUs.}
}
@TechReport{ it:2013-019,
author = {Emil Kieri and Gunilla Kreiss and Olof Runborg},
title = {Coupling of {G}aussian Beam and Finite Difference Solvers
for Semiclassical {S}chr{\"o}dinger Equations},
institution = it,
department = tdb,
year = 2013,
number = {2013-019},
month = sep,
abstract = {In the semiclassical regime, solutions to the
time-dependent Schr{\"o}dinger equation are highly
oscillatory. The number of grid points required for
resolving the oscillations may become very large even for
simple model problems, making solution on a grid, e.g.,
using a finite difference method, intractable. Asymptotic
methods like Gaussian beams can resolve the oscillations
with little effort and yield good approximations when the
molecules are heavy and the potential is smooth. However,
when the potential has variations on a small length-scale,
quantum phenomena become important. Then asymptotic methods
are less accurate. The two classes of methods perform well
in different parameter regimes. This opens for hybrid
methods, using Gaussian beams where we can and finite
differences where we have to. We propose a new method for
treating the coupling between the finite difference method
and Gaussian beams. The new method reduces the needed
amount of overlap regions considerably compared to previous
methods, which improves the efficiency. We apply the method
to scattering problems in one and two dimensions. }
}
@TechReport{ it:2013-018,
author = {Martin Almquist and Ilkka Karasalo and Ken Mattsson},
title = {Atmospheric Sound Propagation over Large-Scale Irregular
Terrain},
institution = it,
department = tdb,
year = 2013,
number = {2013-018},
month = sep,
abstract = {A benchmark problem on atmospheric sound propagation over
irregular terrain has been solved using a stable
fourth-order accurate finite difference approximation of a
high-fidelity acoustic model. A comparison with the
parabolic equation method and ray tracing methods is made.
The results show that ray tracing methods can potentially
be unreliable in the presence of irregular terrain.}
}
@TechReport{ it:2013-017,
author = {T. S{\"o}derstr{\"o}m and J. Yuz},
title = {Analysing Model Validation Methods for Errors-in-Variables
Estimation},
institution = it,
department = syscon,
year = 2013,
number = {2013-017},
month = sep,
abstract = {When identifying a dynamic system the model has to be
validated as well. For an errors-in-variables situation
where both input and output measurements are noise
corrupted, this is a nontrivial task, seldom treated in the
literature. Some different approaches for model validation
are introduced and evaluated by theoretical analysis as
well as application to simulated data.}
}
@TechReport{ it:2013-016,
author = {Ken Mattsson and Martin Almquist and Mark H. Carpenter},
title = {Optimal Diagonal-Norm {SBP} Operators},
institution = it,
department = tdb,
year = 2013,
number = {2013-016},
month = sep,
abstract = {Optimal boundary closures are derived for first
derivative, finite difference operators of order $2$, $4$,
$6$ and $8$. The closures are based on a diagonal-norm
summation-by-parts (SBP) framework, thereby guaranteeing
linear stability on piecewise curvilinear multi-block grids
and entropy stability for nonlinear equations that support
a convex extension. The new closures are developed by
enriching conventional approaches with additional boundary
closure stencils and non-equidistant grid distributions at
the domain boundaries. Greatly improved accuracy is
achieved near the boundaries, as compared with traditional
diagonal norm operators of the same order. The superior
accuracy of the new optimal diagonal-norm SBP operators is
demonstrated for linear hyperbolic systems in one dimension
and for the nonlinear compressible Euler equations in two
dimensions.}
}
@TechReport{ it:2013-015,
author = {Olov Ros{\'e}n and Alexander Medvedev},
title = {Parallel Recursive Bayesian Estimation on Multicore
Computational Platforms Using Orthogonal Basis Functions},
institution = it,
department = syscon,
year = 2013,
number = {2013-015},
month = aug,
abstract = {A method to solve the recursive Bayesian estimation
problem by making use of orthogonal series expansions of
the involved probability density functions is presented.
The coefficients of the expansion for the posterior density
are then calculated recursively via prediction and update
equations. The method has two main benefits: it provides
high estimation accuracy at a relatively low computational
cost and it is highly amenable to parallel implementation.
An application to a bearings-only tracking problem shows
that the proposed method performs with the same accuracy as
the particle filter but at a 24 times lower computational
cost. A parallel implementation on a shared-memory
multicore machine demonstrates that linear speedup in the
number of cores is achievable.}
}
@TechReport{ it:2013-014,
author = {{\AA}man Pohjola, Johannes and Johannes Borgstr{\"o}m and
Joachim Parrow and Palle Raabjerg and Ioana Rodhe},
title = {Negative Premises in Applied Process Calculi},
institution = it,
department = csd,
year = 2013,
number = {2013-014},
month = jun,
abstract = {We explore two applications of negative premises to
increase the expressive power of psi-calculi: reliable
broadcasts and priorities. Together, these can be used to
model discrete time, which we illustrate with an example
from automotive applications. The negative premises can be
encoded by a two-level structural operational semantics
without negative premises; we use this fact to prove the
standard congruence and structural laws of bisimulation
with Nominal Isabelle.}
}
@TechReport{ it:2013-013,
author = {Jens Berg and Jan Nordstr{\"o}m},
title = {Duality Based Boundary Conditions and Dual Consistent
Finite Difference Discretizations of the {N}avier-{S}tokes
and {E}uler Equations},
institution = it,
department = tdb,
year = 2013,
number = {2013-013},
month = may,
abstract = {In this paper we derive new farfield boundary conditions
for the time-dependent Navier-Stokes and Euler equations in
two space dimensions. The new boundary conditions are
derived by simultaneously considering well-posedess of both
the primal and dual problems. We moreover require that the
boundary conditions for the primal and dual Navier-Stokes
equations converge to well-posed boundary conditions for
the primal and dual Euler equations.
We perform computations with a high-order finite difference
scheme on summation-by-parts form with the new boundary
conditions imposed weakly by the simultaneous approximation
term. We prove that the scheme is both energy stable and
dual consistent and show numerically that both linear and
non-linear integral functionals become superconvergent.}
}
@TechReport{ it:2013-012,
author = {Mikael Erlandsson and Anders Jansson},
title = {General Domain Properties in Vehicle Operation: A
Comparison between Trains and High-Speed Ferries},
institution = it,
department = vi2,
year = 2013,
number = {2013-012},
month = may,
abstract = {This paper focus on decision making in the domain of
vehicle driving, and the goal is to find out what
train-drivers have in common with officers of high-speed
ferries in terms of general domain properties. Such
properties may be important to identify because they can
say something about what constraints these rather diverse
work domains may have in common. Consequently, design ideas
within one domain can be transferred to another, bearing in
mind that tasks, strategies as well as domain-specific
knowledge and worker competencies, still have to be
introduced in the final design of any artefact. A new
information acquisition method called collegial
verbalisation is used to study vehicle drivers of trains
and high speed ferries. Central properties of the vehicle
operators' work are identified, and a comparison is made
between the two very different types of vehicles. Three
specific topics from the results are discussed in detail,
and some conclusions are made about the generality of them
with respect to other domains in transportation. Two of the
topics, operators' spatial division and temporal
perspective, are also discussed in relation to the concept
of situation awareness.}
}
@TechReport{ it:2013-011,
author = {Daniel Elfverson and Axel M{\aa}lqvist},
title = {Discontinuous {G}alerkin Multiscale Methods for Convection
Dominated Problems},
institution = it,
department = tdb,
year = 2013,
number = {2013-011},
month = may,
abstract = {We propose an extension of the discontinuous Galerkin
multiscale method, presented in [11], to convection
dominated problems with rough, heterogeneous, and highly
varying coefficients. The properties of the multiscale
method and the discontinuous Galerkin method allows us to
better cope with multiscale features as well as boundary
layers in the solution. In the proposed method the trail
and test spaces are spanned by a corrected basis calculated
on localized patches of size $\mathcal{O}(H\log(H^{-1}))$,
where $H$ is the mesh size. We prove convergence rates
independent of the variation in the coefficients and
present numerical experiments which verify the analytical
findings.}
}
@TechReport{ it:2013-010,
author = {Mark B. Flegg and Stefan Hellander and Radek Erban},
title = {Convergence of Methods for Coupling of Microscopic and
Mesoscopic Reaction-Diffusion Simulations},
institution = it,
department = tdb,
year = 2013,
number = {2013-010},
month = apr,
abstract = {In this paper, three multiscale methods for coupling of
mesoscopic (compartment-based) and microscopic
(molecular-based) stochastic reaction-diffusion simulations
are investigated. Two of the three methods that will be
discussed in detail have been previously reported in the
literature; the two-regime method (TRM) and the
compartment-placement method (CPM). The third method that
is introduced and analysed in this paper is the ghost cell
method (GCM). Presented is a comparison of sources of
error. The convergent properties of this error are studied
as the time step $\Delta t$ (for updating the
molecular-based part of the model) approaches zero. It is
found that the error behaviour depends on another
fundamental computational parameter $h$, the compartment
size in the mesoscopic part of the model. Two important
limiting cases, which appear in applications, are
considered: \par $\,$(i) $\Delta t \to 0$ and $h$ is fixed;
\par (ii) $\Delta t \to 0$ and $h \rightarrow 0$ such that
$\sqrt{\Delta t}/h$ is fixed. \\ The error for previously
developed approaches (the TRM and CPM) converges to zero
only in the limiting case (ii), but not in case (i). It is
shown that the error of the GCM converges in the limiting
case (i). Thus the GCM is superior to previous coupling
techniques if the mesoscopic description is much coarser
than the microscopic part of the model.}
}
@TechReport{ it:2013-009,
author = {Stefan Hellander},
title = {Single Molecule Simulations in Complex Geometries with
Embedded Dynamic One-Dimensional Structures},
institution = it,
department = tdb,
year = 2013,
number = {2013-009},
month = apr,
abstract = {Stochastic models of reaction-diffusion systems are
important for the study of bio- chemical reaction networks
where species are present in low copy numbers or if reac-
tions are highly diffusion limited. In living cells many
such systems include reactions and transport on
one-dimensional structures, such as DNA and microtubules.
The cytoskeleton is a dynamic structure where individual
fibers move, grow and shrink. In this paper we present a
simulation algorithm that combines single molecule simula-
tions in three-dimensional space with single molecule
simulations on one-dimensional structures of arbitrary
shape. Molecules diffuse and react with each other in
space, they associate to and dissociate from
one-dimensional structures as well as diffuse and react
with each other on the one-dimensional structure. A general
curve embed- ded in space can be approximated by a
piecewise linear curve to arbitrary accuracy. The resulting
algorithm is hence very flexible. Molecules bound to a
curve can move by pure diffusion or via active transport,
and the curve can move in space as well as grow and shrink.
The flexibility and accuracy of the algorithm is
demonstrated in four numerical examples.}
}
@TechReport{ it:2013-008,
author = {Nan Guan and Pontus Ekberg and Martin Stigge and Wang Yi},
title = {Improving the Scheduling of Certifiable Mixed-Criticality
Sporadic Task Systems},
institution = it,
department = docs,
year = 2013,
number = {2013-008},
month = apr,
abstract = {An increasing trend in embedded system design is to
integrate components with different levels of criticality
into a shared hardware platform for better cost and power
efficiency. Such mixed-criticality systems are subject to
certifications at different levels of rigorousness, for
validating the correctness of different subsystems on
various confidence levels. The realtime scheduling of
certifiable mixed-criticality systems has been recognized
to be a challenging problem, where using traditional
scheduling techniques may result in unacceptable resource
waste. In this paper we present an algorithm called PLRS to
schedule certifiable mixed-criticality sporadic tasks
systems. PLRS uses fixed-job-priority scheduling, and
assigns job priorities by exploring and balancing the
asymmetric effects between the workload on different
criticality levels. Comparing with the state-of-the-art
algorithm by Li and Baruah for such systems, which we refer
to as LB, PLRS is both more effective and more efficient:
(i) The schedulability test of PLRS not only theoretically
dominates, but also on average significantly outperforms
LB~s. (ii) The run-time complexity of PLRS is polynomial
(quadratic in the number of tasks), which is much more
efficient than the pseudo-polynomial run-time complexity of
LB.}
}
@TechReport{ it:2013-007,
author = {Emil Kieri},
title = {Accelerated Convergence for {S}chr{\"o}dinger Equations
with Non-Smooth Potentials},
institution = it,
department = tdb,
year = 2013,
number = {2013-007},
month = apr,
abstract = {When numerically solving the time-dependent
Schr{\"o}dinger equation for the electrons in an atom or
molecule, the Coulomb singularity poses a challenge. The
solution will have limited regularity, and high-order
spatial discretisations, which are much favoured in the
chemical physics community, are not performing to their
full potential. By exploiting knowledge about the jumps in
the derivatives of the solution we construct a correction,
and show how this improves the convergence rate of Fourier
collocation from second to fourth order. This allows for a
substantial reduction in the number of grid points. The new
method is applied to the higher harmonic generation from
atomic hydrogen.}
}
@TechReport{ it:2013-006,
author = {Torbj{\"o}rn Wigren and Johan Schoukens},
title = {Data for Benchmarking in Nonlinear System Identification},
institution = it,
department = syscon,
year = 2013,
number = {2013-006},
month = mar,
note = {The data can be downloaded from
\url{http://www.it.uu.se/research/publications/reports/2013-006/SNLA80mVZipped.zip}.}
,
abstract = {System identification is a fundamentally experimental
field of science in that it deals with modeling of system
dynamics using measured data. Despite this fact many
algorithms and theoretical results are only tested with
simulations at the time of publication. One reason for this
may be a lack of easily available live data. This paper
therefore presents three sets of data, suitable for
development, testing and benchmarking of system
identification algorithms for nonlinear systems. The data
sets are collected from laboratory processes that can be
described by block ~ oriented dynamic models, and by more
general nonlinear difference and differential equation
models. All data sets are available for free download.}
}
@TechReport{ it:2013-005,
author = {Owe Axelsson and Maya Neytcheva and Bashir Ahmad},
title = {A Comparison of Iterative Methods to Solve Complex Valued
Linear Algebraic Systems},
institution = it,
department = tdb,
year = 2013,
number = {2013-005},
month = mar,
abstract = {Complex valued linear algebraic systems arise in many
important applications. We present analytical and extensive
numerical comparisons of some available numerical solution
methods. It is advocated, in particular for large scale
ill-conditioned problems, to rewrite the complex-valued
system in real valued form leading to a two-by-two block
system of particular form, for which it is shown that a
very efficient and robust preconditioned iterative solution
methods can be constructed. Alternatively, in many cases it
turns out that a simple preconditioner in the form of the
sum of the real and the imaginary part of the matrix also
works well but involves complex arithmetics. }
}
@TechReport{ it:2013-004,
author = {Peter Hansbo and Mats G. Larson and Sara Zahedi},
title = {Characteristic Cut Finite Element Methods for
Convection-Diffusion Problems on Time Dependent Surfaces},
institution = it,
department = tdb,
year = 2013,
number = {2013-004},
month = mar,
abstract = {We develop a finite element method for convection
diffusion problems on a given time dependent surface, for
instance modeling the evolution of a surfactant. The method
is based on a characteristic-Galerkin formulation combined
with a piecewise linear cut finite element method in space.
The cut finite element method is constructed by embedding
the surface in a background grid and then using the
restriction to the surface of a finite element space
defined on the background grid. The surface is allowed to
cut through the background grid in an arbitrary fashion. To
ensure well posedness of the resulting algebraic systems of
equations, independent of the position of the surface in
the background grid, we add a consistent stabilization
term. We prove error estimates and present confirming
numerical results.}
}
@TechReport{ it:2013-003,
author = {Rebecka Janols and Bengt G{\"o}ransson and Bengt Sandblad},
title = {Slutrapport f{\"o}r Projektet {IVAN} 2008-2011},
institution = it,
department = vi2,
year = 2013,
number = {2013-003},
month = mar,
note = {In Swedish.},
abstract = {Projektet IVAN (Informationssystem i v{\aa}rden
Anv{\"a}ndbarhet och nytta) var ett samarbetsprojekt mellan
Landstinget Uppsala L{\"a}n (LUL) och forskare vid
institutionen f{\"o}r informationsteknologi, avdelningen
m{\"a}nniska datorinteraktion vid Uppsala universitet (UU).
Projektet startade med en f{\"o}rstudie p{\aa} Akademiska
sjukhuset h{\"o}sten 2008 och har mellan jan 2010- dec 2011
fungerat som ett Landstingsprojekt. Det {\"o}vergripande
m{\aa}let med IVAN var att skapa en b{\"a}ttre
anv{\"a}ndning av IT i v{\aa}rden lokalt p{\aa} LUL:s
f{\"o}rvaltningar (Akademiska sjukhuset,
Prim{\"a}rv{\aa}rden, Hj{\"a}lpmedel och habilitering samt
lasarettet i Enk{\"o}ping).I den h{\"a}r rapporten
presenteras slutsatser fr{\aa}n 2.5 {\aa}rs forskarstudier.}
}
@TechReport{ it:2013-002,
author = {Rebecka Janols and Bengt Sandblad and Bengt G{\"o}ransson
and Thomas Lind},
title = {Anv{\"a}ndarnas synpunkter p{\aa} {IT}-l{\"o}sningar i
v{\aa}rden - {S}ammanfattande erfarenheter fr{\aa}n
utv{\"a}rderingar vid {L}andstinget i {U}ppsala l{\"a}n
(2008-2012)},
institution = it,
department = vi2,
year = 2013,
number = {2013-002},
month = mar,
note = {In Swedish. Updated title 2013-03-16.},
abstract = {Det st{\"a}ndigt p{\aa}g{\aa}ende
IT-f{\"o}r{\"a}ndringsarbetet inom v{\aa}rden har
potentialen att bidra till {\"o}kad v{\aa}rdkvalitet,
effektivitet, patients{\"a}kerhet, patientservice och en
f{\"o}rb{\"a}ttrad arbetsmilj{\"o}. Om man lyckas med detta
{\"a}r IT-investeringar nyttiga f{\"o}r v{\aa}rden,
patienterna och landstinget. Idag finns emellertid en
d{\aa}lig kunskap om vilken nyttan {\"a}r och det saknas
modeller f{\"o}r att ber{\"a}kna den. All erfarenhet
fr{\aa}n det hittills genomf{\"o}rda arbetet, liksom
fr{\aa}n mycket annan tidigare forskning, pekar p{\aa} att
det finns stora problem med utveckling och inf{\"o}rande av
IT i v{\aa}rden. Problemen best{\aa}r dels i att man inte
f{\"o}rm{\aa}r utnyttja den nyttopotential som finns, dels
att s{\aa}v{\"a}l IT-system som
f{\"o}r{\"a}ndringsprocesserna inte h{\aa}ller nog h{\"o}g
kvalitet, vilket resulterar i negativa reaktioner och
effekter hos anv{\"a}ndarna, dvs. hos v{\aa}rdpersonalen.
Denna rapport presenterar en sammanfattning av
anv{\"a}ndarnas synpunkter p{\aa} IT l{\"o}sningar i
v{\aa}rden. Inneh{\aa}llet i rapporten {\"a}r grundat i
b{\aa}de kvalitativa och kvantitativa studier genomf{\"o}rt
inom ramen for projektet IVAN. Projektet IVAN
(Informationssystem i v{\aa}rden Anv{\"a}ndbarhet och
Nytta) {\"a}r ett samarbetsprojekt mellan Landstinget
Uppsala L{\"a}n (LUL) och forskare vid avdelningen for
visuell information och interaktion, Institutionen f{\"o}r
informationsteknologi vid Uppsala universitet. Projektet
startade med en 6 m{\aa}naders f{\"o}rstudie p{\aa}
Akademiska sjukhuset h{\"o}sten 2008 och har mellan jan
2010- dec 2011 fungerat som ett Landstingsprojekt.
Projektet var ett IVAN har till stor del fokuserat p{\aa}
kartl{\"a}ggningar och analyser av de system, processer och
organisation som finns runt dagens IT-system. Bilden av de
problem som finns idag, s{\"a}rskilt n{\"a}r det g{\"a}ller
v{\aa}rdpersonalens upplevda situation, har klarnat.
M{\aa}nga behov av f{\"o}r{\"a}ndringar och f{\"o}rb{\"a}ttringar har framkommit. }
}
@TechReport{ it:2013-001,
author = {Rebecka Janols and Erik Bor{\"a}lv},
title = {{I}nformationssystem i {V}{\aa}rden ~ {A}nv{\"a}ndbarhet
och {N}ytta ({IVAN}). F{\"o}rstudierapport 2008.},
institution = it,
department = vi2,
year = 2013,
number = {2013-001},
month = jan,
note = {In Swedish. Updated title 2013-03-16.},
abstract = {Under h{\"o}sten 2008 har ett samarbetsprojekt mellan
Akademiska sjukhuset och Uppsala universitet
p{\aa}b{\"o}rjats. Det har handlat om att fram mer
anv{\"a}ndbara IT-st{\"o}d d{\"a}r m{\aa}let {\"a}r att
IT-anv{\"a}ndningen ska bidra till ett effektivt och
h{\aa}llbart arbete. Under h{\"o}sten har vi genomf{\"o}rt
aktiviteter i form av intervjuer, observationer,
enk{\"a}ter samt medverkat i olika personalaktiviteter
p{\aa} tre enheter p{\aa} Akademiska sjukhuset:
ortopedmottagningen, 30e och 96c. Slutsatserna presenterar
vi i form av fem {\"o}vergripande rekommendationer
inf{\"o}r det fortsatta arbetet. De fem rekommendationerna
{\"a}r: 1) Upps{\"o}kande supportverksamhet, 2) Jourhavande
jurist, 3) Mandat, 4) Utv{\"a}rdera samt 5) utbildning.}
}
@TechReport{ it:2012-036,
author = {Pavol Bauer and Brian Drawert and Stefan Engblom and
Andreas Hellander},
title = {URDME v. 1.2: User's manual},
institution = it,
department = tdb,
year = 2012,
number = {2012-036},
month = dec,
note = {Also available at \url{http://arxiv.org/abs/0902.2912}},
abstract = {We have developed URDME, a general software for simulation
of stochastic reaction-diffusion processes on unstructured
meshes. This allows for a more flexible handling of
complicated geometries and curved boundaries compared to
simulations on structured, cartesian meshes. The underlying
algorithm is the next subvolume method, extended to
unstructured meshes by obtaining jump coefficients from a
finite element formulation of the corresponding macroscopic
equation. This manual describes version 1.2 of the
software. URDME 1.2 includes support for Comsol
Multiphysics 4.1, 4.2, 4.3 as well as the previous version
3.5a. Additionally, support for basic SBML has been added
along with the possibility to compile in stand-alone
mode.}
}
@TechReport{ it:2012-035,
author = {Per Pettersson and Gianluca Iaccarino and Jan
Nordstr{\"o}m},
title = {An Intrusive Hybrid Method for Discontinuous Two-Phase
Flow under Uncertainty},
institution = it,
department = tdb,
year = 2012,
number = {2012-035},
month = dec,
abstract = {An intrusive stochastic projection method for two-phase
time-dependent flow subject to uncertainty is presented.
Numerical experiments are carried out assuming uncertainty
in the interface location, but the framework generalizes to
uncertainty with known distribution in other input data.
Uncertainty is represented through a truncated multiwavelet
expansion.
We assume that the discontinuous features of the solution
are restricted to subdomains in the computational domain
and use a high-order method for the smooth regions coupled
weakly through interfaces with a robust shock capturing
method for the non-smooth regions.
The discretization of the non-smooth region is based on a
generalization of the HLL flux, and have many properties in
common with its deterministic counterpart. It is simple and
robust, and captures the statistics of the shock. The
discretization of the smooth region is carried out with
high-order finite-difference operators satisfying a
summation-by-parts property.}
}
@TechReport{ it:2012-034,
author = {Siyang Wang and Johan Elf and Stefan Hellander and Per
L{\"o}tstedt},
title = {Stochastic Reaction-Diffusion Processes with Embedded
Lower Dimensional Structures},
institution = it,
department = tdb,
year = 2012,
number = {2012-034},
month = dec,
abstract = {Small copy numbers of many molecular species in biological
cells require stochastic models of the chemical reactions
between the molecules and their motion. Important reactions
often take place on one dimensional structures embedded in
three dimensions with molecules migrating between the
dimensions. Examples of polymer structures in cells are
DNA, microtubules, and actin filaments. An algorithm for
simulation of such systems is developed at a mesoscopic
level of approximation. An arbitrarily shaped polymer is
coupled to a background Cartesian mesh in three dimensions.
The realization of the system is made with a stochastic
simulation algorithm in the spirit of Gillespie. The method
is applied to model problems for verification and two more
detailed models of transcription factor interaction with
the DNA.}
}
@TechReport{ it:2012-033,
author = {Per Pettersson and Gianluca Iaccarino and Jan
Nordstr{\"o}m},
title = {A Stochastic {G}alerkin Method for the {E}uler Equations
with {R}oe Variable Transformation},
institution = it,
department = tdb,
year = 2012,
number = {2012-033},
month = nov,
note = {This is a complete rewrite of report nr 2012-021 with new
results. A more general framework for the representation of
uncertainty is used. All figures have been replaced and
more numerical results have been added (methods of
manufactured solutions, convergence in space and the
stochastic dimension for subsonic and supersonic flow).},
abstract = {The Euler equations subject to uncertainty in the initial
and boundary conditions are investigated via the stochastic
Galerkin approach. We present a new fully intrusive method
based on a variable transformation of the continuous
equations. Roe variables are employed to get quadratic
dependence in the flux function and a well-defined Roe
average matrix that can be determined without matrix
inversion.
In previous formulations based on generalized polynomial
chaos expansion of the physical variables, the need to
introduce stochastic expansions of inverse quantities, or
square-roots of stochastic quantities of interest, adds to
the number of possible different ways to approximate the
original stochastic problem. We present a method where the
square roots occur in the choice of variables and no
auxiliary quantities are needed, resulting in an
unambiguous problem formulation.
The Roe formulation saves computational cost compared to
the formulation based on expansion of conservative
variables. Moreover, the Roe formulation is more robust and
can handle cases of supersonic flow, for which the
conservative variable formulation fails to produce a
bounded solution. We use a multi-wavelet basis that can be
chosen to include a large number of resolution levels to
handle more extreme cases (e.g. strong discontinuities) in
a robust way. For smooth cases, the order of the polynomial
representation can be increased for increased accuracy.}
}
@TechReport{ it:2012-032,
author = {Sofia Eriksson and Jan Nordstr{\"o}m},
title = {Exact Non-Reflecting Boundary Conditions Revisited:
Well-Posedness and Stability},
institution = it,
department = tdb,
year = 2012,
number = {2012-032},
month = oct,
abstract = {Exact non-reflecting boundary conditions for an
incompletely parabolic system have been studied. It is
shown that well-posedness is a fundamental property of the
non-reflecting boundary conditions. By using summation by
parts operators for the numerical approximation and a weak
boundary implementation, energy stability follows
automatically. The stability in combination with the high
order accuracy results in a reliable, efficient and
accurate method. The theory is supported by numerical
simulations. }
}
@TechReport{ it:2012-031,
author = {Parosh Aziz Abdulla and Mohamed Faouzi Atig and Jonathan
Cederberg},
title = {Timed Lossy Channel Systems},
institution = it,
department = docs,
year = 2012,
number = {2012-031},
month = oct,
abstract = {Lossy channel systems are a classical model with
applications ranging from the modeling of communication
protocols to programs running on weak memory models. All
existing work assume that messages traveling inside the
channels are picked from a finite alphabet. In this paper,
we extend the model by assuming that each message is
equipped with a clock representing the age of the message,
thus obtaining the model of \emph{Timed Lossy Channel
Systems (TLCS)}. The main contribution of the paper is to
show that the control state reachability problem is
decidable for TLCS.}
}
@TechReport{ it:2012-030,
author = {David Ekl{\"o}v and Nikos Nikoleris and Erik Hagersten},
title = {A Profiling Method for Analyzing Scalability Bottlenecks
on Multicores},
institution = it,
department = docs,
year = 2012,
number = {2012-030},
month = oct,
abstract = {A key goodness metric of multi-threaded programs is how
their execution times scale when increasing the number of
threads. However, there are several bottlenecks that can
limit the scalability of a multi-threaded program, e.g.,
contention for shared cache capacity and off-chip memory
bandwidth; and synchronization overheads. In order to
improve the scalability of a multi-threaded program, it is
vital to be able to quantify how the program is impacted by
these scalability bottlenecks.
We present a software-only profiling method for obtaining
{\it speedup stacks}. A speedup stack reports how much each
scalability bottleneck limits the scalability of a
multi-threaded program. It thereby quantifies how much its
scalability can be improved by eliminating a given
bottleneck. A software developer can use this information
to determine what optimizations are most likely to improve
scalability, while a computer architect can use it to
analyze the resource demands of emerging workloads.
The proposed method profiles the program on real commodity
multi-cores (i.e., no simulations required) using existing
performance counters. Consequently, the obtained speedup
stacks accurately account for all idiosyncrasies of the
machine on which the program is profiled. While the main
contribution of this paper is the profiling method to
obtain speedup stacks, we present several examples of how
speedup stacks can be used to analyze the resource
requirements of multi-threaded programs. Furthermore, we
discuss how their scalability can be improved by both
software developers and computer architects.}
}
@TechReport{ it:2012-029,
author = {David Ekl{\"o}v and Nikos Nikoleris and David
Black-Schaffer and Erik Hagersten},
title = {Quantitative Characterization of Memory Contention},
institution = it,
department = docs,
year = 2012,
number = {2012-029},
month = oct,
abstract = {On multicore processors, co-executing applications compete
for shared resources, such as cache capacity and memory
bandwidth. This leads to suboptimal resource allocation and
can cause substantial performance loss, which makes it
important to effectively manage these shared resources.
This, however, requires insights into how the applications
are impacted by such resource sharing.
While there are several methods to analyze the performance
impact of cache contention, less attention has been paid to
general, quantitative methods for analyzing the impact of
contention for memory bandwidth. To this end we introduce
the \textit{Bandwidth Bandit}, a general, quantitative,
profiling method for analyzing the performance impact of
contention for memory bandwidth on multicore machines.
The profiling data captured by the Bandwidth Bandit is
presented in a {\it bandwidth graph}. This graph accurately
captures the measured application's performance as a
function of its available memory bandwidth, and enables us
to determine how much the application suffers when its
available bandwidth is reduced. To demonstrate the value of
this data, we present a case study in which we use the
bandwidth graph to analyze the performance impact of memory
contention when co-running multiple instances of single
threaded application.}
}
@TechReport{ it:2012-028,
author = {Per Pettersson and Alireza Doostan and Jan Nordstr{\"o}m},
title = {On Stability and Monotonicity Requirements of Discretized
Stochastic Conservation Laws with Random Viscosity},
institution = it,
department = tdb,
year = 2012,
number = {2012-028},
month = sep,
abstract = {The stochastic Galerkin and collocation methods are used
to solve an advection-diffusion equation with uncertain and
spatially varying viscosity. We investigate well-posedness,
monotonicity and stability for the extended system
resulting from the Galerkin projection of the
advection-diffusion equation onto the stochastic basis
functions. High-order summation-by-parts operators and weak
imposition of boundary conditions are used to prove
stability of the semi-discrete system.
It is essential that the eigenvalues of the resulting
viscosity matrix of the stochastic Galerkin system are
positive and we investigate conditions for this to hold.
When the viscosity matrix is diagonalizable, stochastic
Galerkin and stochastic collocation are similar in terms of
computational cost, and for some cases the accuracy is
higher for stochastic Galerkin provided that monotonicity
requirements are met. We also investigate the total spatial
operator of the semi-discretized system and its impact on
the convergence to steady-state.}
}
@TechReport{ it:2012-027,
author = {Carl Nettelblad},
title = {Breakdown of Methods for Phasing and Imputation in the
Presence of Double Genotype Sharing},
institution = it,
department = tdb,
year = 2012,
number = {2012-027},
month = sep,
abstract = {In genome-wide association studies, results have been
improved through imputation of a denser marker set based on
reference haplotypes and phasing of the genotype data. To
better handle very large sets of reference haplotypes,
pre-phasing with only study individuals has been suggested.
We present a possible problem which is aggravated when
pre-phasing strategies are used, and suggest a modification
avoiding these issues with application to the MaCH tool.
We evaluate the effectiveness of our remedy to a subset of
Hapmap data, comparing the original version of MaCH and our
modified approach. Improvements are demonstrated on the
original data (phase switch error rate decresasing by
10\%), but the differences are more pronounced in cases
where the data is augmented to represent the presence of
closely related individuals, especially when siblings are
present (30\% reduction in switch error rate in the
presence of children, 47\% reduction in the presence of
siblings). When introducing siblings, the switch error rate
in results from the unmodified version of MaCH increases
significantly compared to the original data.
The main conclusions of this investigation is that existing
statistical methods for phasing and imputation of unrelated
individuals might give subpar quality results if a subset
of study individuals nonetheless are related. As the
populations collected for general genome-wide association
studies grow in size, including relatives might become more
common. If a general GWAS framework for unrelated
individuals would be employed on datasets where
sub-populations originally collected as familial
case-control sets are included, caution should also be
taken regarding the quality of haplotypes.
Our modification to MaCH is available on request and
straightforward to implement. We hope that this mode, if
found to be of use, could be integrated as an option in
future standard distributions of MaCH.}
}
@TechReport{ it:2012-026,
author = {Carl Nettelblad},
title = {Inferring Haplotypes and Parental Genotypes in Larger Full
Sib-Ships and Other Pedigrees with Missing or Erroneous
Genotype Data},
institution = it,
department = tdb,
year = 2012,
number = {2012-026},
month = sep,
abstract = {\textbf{Background:} In many contexts, pedigrees for
individuals are known even though not all individuals have
been fully genotyped. In one extreme case, the genotypes
for a set of full siblings are known, with no knowledge of
parental genotypes. We propose a method for inferring
phased haplotypes and genotypes for all individuals, even
those with missing data, in such pedigrees, allowing a
multitude of classic and recent methods for linkage and
genome analysis to be used more efficiently.
\textbf{Results:} By artificially removing the founder
generation genotype data from a well-studied simulated
dataset, the quality of reconstructed genotypes in that
generation can be verified. For the full structure of
repeated matings with $15$ offspring per mating, $10$ dams
per sire, $99.89\%$ of all founder markers were phased
correctly, given only the unphased genotypes for offspring.
The accuracy was reduced only slightly, to $99.51\%$, when
introducing a $2\%$ error rate in offspring genotypes. When
reduced to only $5$ full-sib offspring in a single sire-dam
mating, the corresponding percentage is $92.62\%$, which
compares favorably with $89.28\%$ from the leading Merlin
package. Furthermore, Merlin is unable to handle more than
approximately $10$ sibs, as the number of states tracked
rises exponentially with family size, while our approach
has no such limit and handles $150$ half-sibs with ease in
our experiments.
\textbf{Conclusions:} Our method is able to reconstruct
genotypes for parents when genotype data is only available
for offspring individuals, as well as haplotypes for all
individuals. Compared to the Merlin package, we can handle
larger pedigrees and produce superior results, mainly due
to the fact that Merlin uses the Viterbi algorithm on the
state space to infer the genotype sequence. Tracking of
haplotype and allele origin can be used in any application
where the marker set does not directly influence genotype
variation influencing traits. Inference of genotypes can
also reduce the effects of genotyping errors and missing
data. The \texttt{cnF2freq} codebase implementing our
approach is available under a BSD-style license.}
}
@TechReport{ it:2012-025,
author = {Jens Berg and Jan Nordstr{\"o}m},
title = {On the Impact of Boundary Conditions on Dual Consistent
Finite Difference Discretizations},
institution = it,
department = tdb,
year = 2012,
number = {2012-025},
month = sep,
abstract = {In this paper we derive well-posed boundary conditions for
a linear incompletely parabolic system of equations, which
can be viewed as a model problem for the compressible
Navier-Stokes equations. We show a general procedure for
the construction of the boundary conditions such that both
the primal and dual equations are well-posed. The form of
the boundary conditions is chosen such that reduction to
first order form with its complications can be avoided.
The primal equation is discretized using finite difference
operators on summation-by-parts form with weak boundary
conditions. It is shown that the discretization can be made
energy stable, and that energy stability is sufficient for
dual consistency. Since reduction to first order form can
be avoided, the discretization is significantly simpler
compared to a discretization using Dirichlet boundary
conditions.
We compare the new boundary conditions with standard
Dirichlet boundary conditions in terms of rate of
convergence, errors and discrete spectra. It is shown that
the scheme with the new boundary conditions is not only far
simpler, but have smaller errors, error bounded properties,
and highly optimizable eigenvalues, while maintaining all
desirable properties of a dual consistent discretization.}
}
@TechReport{ it:2012-024,
author = {Katharina Kormann and Elisabeth Larsson},
title = {An {RBF}-{G}alerkin Approach to the Time-Dependent
{S}chr{\"o}dinger Equation},
institution = it,
department = tdb,
year = 2012,
number = {2012-024},
month = sep,
abstract = {In this article, we consider the discretization of the
time-dependent Schrödinger equation using radial basis
functions (RBF). We formulate the discretized problem over
an unbounded domain without imposing explicit boundary
conditions. Since we can show that time-stability of the
discretization is not guaranteed for an RBF-collocation
method, we propose to employ a Galerkin ansatz instead. For
Gaussians, it is shown that exponential convergence is
obtained up to a point where a systematic error from the
domain where no basis functions are centered takes over.
The choice of the shape parameter and of the resolved
region is studied numerically. Compared to the Fourier
method with periodic boundary conditions, the basis
functions can be centered in a smaller domain which gives
increased accuracy with the same number of points.}
}
@TechReport{ it:2012-023,
author = {Katharina Kormann},
title = {A Time-Space Adaptive Method for the {S}chr{\"o}dinger
Equation},
institution = it,
department = tdb,
year = 2012,
number = {2012-023},
month = aug,
note = {Updated 2012-09-12 (typos fixed).},
abstract = {In this paper, we present a discretization of the
time-dependent Schr{\"o}dinger equation based on a
Magnus-Lanczos time integrator and high-order Gauss-Lobatto
finite elements in space. A truncated Galerkin
orthogonality is used to obtain duality-based a posteriori
error estimates that address the temporal and the spatial
error separately. Based on this theory, a space-time
adaptive solver for the Schr{\"o}dinger equation is
devised. An efficient matrix-free implementation of the
differential operator, suited for spectral elements, is
used to enable computations for realistic configurations.
We demonstrate the performance of the algorithm for the
example of matter-field interaction.}
}
@TechReport{ it:2012-022,
author = {Olof Rensfelt and Frederik Hermans and Thiemo Voigt and
Edith Ngai and Lars-{\AA}ke Nord{\'e}n and Per Gunningberg},
title = {{SoNIC}: Classifying and Surviving Interference in
802.15.4-based Sensor Networks},
institution = it,
department = docs,
year = 2012,
number = {2012-022},
month = aug,
abstract = {Sensor networks that use 802.15.4 in the 2.45~GHz ISM band
are prone to radio interference from devices such as
microwave ovens, WiFi devices, and Bluetooth devices.
Interference can cause packet loss and thus reduces network
performance and lifetime. Online detection of interference
in sensor networks is challenging, because nodes cannot
decode foreign transmissions due to incompatibility between
802.15.4 and other technologies.
We present SoNIC, a system that enables sensor networks to
detect and classify cross-technology interference. At the
core of SoNIC lies an interference classification approach
that assigns individual corrupted 802.15.4 packets to
different interference classes. A voting algorithm fuses
the classification results to detect the presence of
interferers. The output of the voting can be used to select
a mitigation strategy. In contrast to other solutions,
SoNIC does not require active spectrum scanning or
specialized hardware. It runs on ordinary TelosB sensor
nodes using Contiki.
This technical report describes the core idea of SoNIC,
selected system aspects of it (including three mitigation
strategies), as well as initial experiments in an office
environment.}
}
@TechReport{ it:2012-021,
author = {Per Pettersson and Gianluca Iaccarino and Jan
Nordstr{\"o}m},
title = {A {R}oe Variable Based Chaos Method for the {E}uler
Equations under Uncertainty},
institution = it,
department = tdb,
year = 2012,
number = {2012-021},
month = aug,
abstract = {The Euler equations subject to uncertainty in the input
parameters are investigated via the stochastic Galerkin
approach. We present a new fully intrusive method based on
a variable transformation of the continuous equations. Roe
variables are employed to get quadratic dependence in the
flux function and a well-defined Roe average matrix that
can be determined without matrix inversion.
In previous formulations based on generalized chaos
expansion of the physical variables, the need to introduce
stochastic expansions of inverse quantities, or
square-roots of stochastic quantities of interest, adds to
the number of possible different ways to approximate the
original stochastic problem. We present a method where no
auxiliary quantities are needed, resulting in an
unambiguous problem formulation.
The Roe formulation saves computational cost compared to
the formulation based on expansion of conservative
variables. Moreover, the Roe formulation is more robust and
can handle cases of supersonic flow, for which the
conservative variable formulation leads to instability. For
more extreme cases, where the global Legendre polynomials
poorly approximate discontinuities in stochastic space, we
use the localized Haar wavelet basis.},
note = {A compete rewrite with new results appears as report nr
2012-033.}
}
@TechReport{ it:2012-020,
author = {Elisabeth Larsson and Erik Lehto and Alfa Heryudono and
Bengt Fornberg},
title = {Stable Computation of Differentiation Matrices and
Scattered Node Stencils Based on {G}aussian Radial Basis
Functions},
institution = it,
department = tdb,
year = 2012,
number = {2012-020},
month = aug,
abstract = {Radial basis function (RBF) approximation has the
potential to provide spectrally accurate function
approximations for data given at scattered node locations.
For smooth solutions, the best accuracy for a given number
of node points is typically achieved when the basis
functions are scaled to be nearly flat. This also results
in nearly linearly dependent basis functions and severe
ill-conditioning of the interpolation matrices. Fornberg,
Larsson, and Flyer recently developed the RBF-QR method
which provides a numerically stable approach to
interpolation with flat and nearly flat Gaussian RBFs. In
this work, we consider how to extend this method to the
task of computing differentiation matrices and stencil
weights in order to solve partial differential equations.
The expressions for first and second order derivative
operators as well as hyperviscosity operators are
established, numerical issues such as how to deal with
non-unisolvency are resolved, and the accuracy and
computational efficiency of the method is tested
numerically. The results indicate that using the RBF-QR
approach for solving PDE problems can be very competitive
compared with using the ill-conditioned direct solution
approach or using variable precision arithmetic to overcome
the conditioning issue.}
}
@TechReport{ it:2012-019,
author = {Owe Axelsson and Xin He and Maya Neytcheva},
title = {Numerical Solution of the Time-Dependent {N}avier-{S}tokes
Equation for Variable Density--Variable Viscosity},
institution = it,
department = tdb,
year = 2012,
number = {2012-019},
month = aug,
abstract = {We consider methods for numerical simulations of variable
density incompressible fluids, modelled by the
Navier-Stokes equations. Variable density problems arise,
for instance, in interfaces between fluids of different
densities in multiphase flows such as appear in porous
media problems. It is shown that by solving the
Navier-Stokes equation for the momentum variable instead of
the velocity, the corresponding saddle point problem, which
arises at each time step, becomes automatically
regularized, enabling elimination of the pressure variable
and leading to a, for the iterative solution, efficient
preconditioning of the arising block matrix. We present
also stability bounds and a second order operator splitting
method. The theory is illustrated by numerical experiments.
For reasons of comparison we also include test results for
a method, based on coupling of the Navier-Stokes equations
with a phase-field model.}
}
@TechReport{ it:2012-018,
author = {Bengt Fornberg and Erik Lehto and Collin Powell},
title = {Stable Calculation of {G}aussian-based {RBF-FD} Stencils},
institution = it,
department = tdb,
year = 2012,
number = {2012-018},
month = aug,
abstract = {Traditional finite difference (FD) methods are designed to
be exact for low degree polynomials. They can be highly
effective on Cartesian-type grids, but may fail for
unstructured node layouts. Radial basis function-generated
finite difference (RBF-FD) methods overcome this problem
and, as a result, provide a much improved geometric
flexibility. The calculation of RBF-FD weights involves a
shape parameter $\varepsilon$. Small values of
$\varepsilon$\ (corresponding to near-flat RBFs) often lead
to particularly accurate RBF-FD formulas. However, the most
straightforward way to calculate the weights (RBF-Direct)
then becomes numerically highly ill-conditioned. In
contrast, the present algorithm remains numerically stable
all the way into the $\varepsilon\rightarrow0$ limit. Like
the RBF-QR algorithm, it uses the idea of finding a
numerically well-conditioned basis function set in the same
function space as is spanned by the ill-conditioned
near-flat original Gaussian RBFs. By exploiting some
properties of the incomplete gamma function, it transpires
that the change of basis can be achieved without dealing
with any infinite expansions. Its strengths and weaknesses
compared the Contour-Pad{\'e}, RBF-RA,\ and RBF-QR
algorithms are discussed.}
}
@TechReport{ it:2012-017,
author = {Xin He and Marcus Holm and Maya Neytcheva},
title = {Efficiently Parallel Implementation of the Inverse
{S}herman-{M}orrison Algorithm},
institution = it,
department = tdb,
year = 2012,
number = {2012-017},
month = aug,
abstract = {We contribute two parallel strategies to compute the exact
and approximate inverse of a dense matrix, based on the
so-called inverse Sherman-Morrison algorithm and
demonstrate their efficiencies on multicore CPU and
GPU-equipped computers. Our methods are shown to be much
better than a common matrix inverse method, yielding up to
12 times faster performance. A comparison of the
performance of the CPU and GPU versions is made and
analyzed with the aid of a performance model.}
}
@TechReport{ it:2012-016,
author = {Xin He and Maya Neytcheva},
title = {On Preconditioning Incompressible Non-{N}ewtonian Flow
Problems},
institution = it,
department = tdb,
year = 2012,
number = {2012-016},
month = aug,
abstract = {This paper concerns preconditioned iterative solution
methods for solving incompressible non-Newtonian
Navier-Stokes equations as arising in regularized Bingham
models. Stable finite element discretization applied to the
linearized equations results in linear systems of saddle
point form. In order to circumvent the difficulties of
efficiently and cheaply preconditioning the Schur
complement of the system matrix, in this paper the
augmented Lagrangian (AL) technique is used to
algebraically transform the original system into an
equivalent one, which does not change the solution and that
is the linear system we intend to solve by some
preconditioned iterative method. For the transformed system
matrix a lower block-triangular preconditioner is proposed.
The crucial point in the AL technique is how to efficiently
solve the modified pivot block involving the velocity. In
this paper an approximation of the modified pivot block is
proposed and an algebraic multi-grid technique is applied
for this approximation. Numerical experiments show that the
AL preconditioner combining with the algebraic multi-grid
solver is quite efficient and robust with respect to the
variation of the mesh size and the regularized parameter of
the Bingham model.}
}
@TechReport{ it:2012-015,
author = {Josefin Ahlkrona and Nina Kirchner and Per L{\"o}tstedt},
title = {A Numerical Study of the Validity of Shallow Ice
Approximations},
institution = it,
department = tdb,
year = 2012,
number = {2012-015},
month = jul,
abstract = {Improving numerical ice sheet models is a very active
field of research. In part, this is because ice sheet
modelling has gained societal relevance in the context of
predictions of future sea level rise. Ice sheet modelling
is however also a challenging mathematical and
computational subject. Since the exact equations governing
ice dynamics, the full Stokes equations, are
computationally expensive to solve, approximations are
crucially needed for many problems. Shallow ice
approximations are a family of approximations derived by
asymptotic expansion of the exact equations in terms of the
aspect ratio, $\epsilon$. Retaining only the zeroth order
terms in this expansion yields the by far most frequently
used approximation; the Shallow Ice Approximation (SIA).
Including terms up to second order yields the Second Order
Shallow Ice Approximation (SOSIA), which is a so-called
higher order model. Here, we study the validity and
accuracy of shallow ice approximations beyond previous
analyses of the SIA. We perform a detailed analysis of the
assumptions behind shallow ice approximations, i.e. of the
order of magnitude of field variables. We do this by using
a numerical solution of the exact equations for ice flow
over a sloping, undulating bed. We also construct
analytical solutions for the SIA and SOSIA and numerically
compute the accuracy for varying $\epsilon$ by comparing to
the exact solution. We find that the assumptions underlying
shallow ice approximations are not entirely appropriate
since they do not account for a high viscosity boundary
layer developing near the ice surface as soon as small
bumps are introduced at the ice base. This boundary layer
is thick and has no distinct border. Other existing
theories which do incorporate the boundary layer are in
better, but not full, agreement with our numerical results.
Our results reveal that neither the SIA nor the SOSIA is as
accurate as suggested by the asymptotic expansion approach.
Also, in SOSIA the ice rheology needs to be altered to
avoid infinite viscosity, though both our analytical and
numerical solutions show that, especially for high bump
amplitudes, the accuracy of the SOSIA is highly sensitive
to this alternation. However, by updating the SOSIA
solution in an iterative manner, we obtain a model which
utilises the advantages of shallow ice approximations,
while reducing the disadvantages.}
}
@TechReport{ it:2012-014,
author = {Jens Berg and Jan Nordstr{\"o}m},
title = {A Stable and Dual Consistent Boundary Treatment Using
Finite Differences on Summation-By-Parts Form},
institution = it,
department = tdb,
year = 2012,
number = {2012-014},
month = jul,
abstract = {This paper is concerned with computing very high order
accurate linear functionals from a numerical solution of a
time-dependent partial differential equation (PDE). Based
on finite differences on summation-by-parts form, together
with a weak implementation of the boundary conditions, we
show how to construct suitable boundary conditions for the
PDE such that the continuous problem is well-posed and the
discrete problem is stable and spatially dual consistent.
These two features result in a superconvergent functional,
in the sense that the order of accuracy of the functional
is provably higher than that of the solution.}
}
@TechReport{ it:2012-013,
author = {Philip Axer and Rolf Ernst and Heiko Falk and Alain
Girault and Daniel Grund and Nan Guan and Bengt Jonsson and
Peter Marwedel and Jan Reineke and Christine Rochange and
Maurice Sebastian and von Hanxleden, Reinhard and Reinhard
Wilhelm and Wang Yi},
title = {Building Timing Predictable Embedded Systems},
institution = it,
department = docs,
year = 2012,
number = {2012-013},
month = jul,
abstract = {A large class of embedded systems is distinguished from
general purpose computing systems by the need to satisfy
strict requirements on timing, often under constraints on
available resources. Predictable system design is concerned
with the challenge of building systems for which timing
requirements can be guaranteed a priori. Perhaps
paradoxically, this problem has become more difficult by
the introduction of performance-enhancing architectural
elements, such as caches, pipelines, and multithreading,
which introduce a large degree of nondeterminism and make
guarantees harder to provide. The intention of this paper
is to summarize current state-of-the-art in research
concerning how to build predictable yet performant systems.
We suggest precise definitions for the concept of
``predictability'', and present predictability concerns at
different abstractions levels in embedded software design.
First, we consider timing predictability of processor
instruction sets. Thereafter, We consider how programming
languages can be equipped with predictable timing
semantics, covering both a language-based approach based on
the synchronous paradigm, as well as an environment that
provides timing semantics for a mainstream programming
language (in this case C). We present techniques for
achieving timing predictability on multicores. Finally we
discuss how to handle predictability at the level of
networked embedded systems, where randomly occurring errors
must be considered.}
}
@TechReport{ it:2012-012,
author = {Anders Goude and Stefan Engblom},
title = {Adaptive Fast Multipole Methods on the {GPU}},
institution = it,
department = tdb,
year = 2012,
number = {2012-012},
month = may,
abstract = {We present a highly general implementation of fast
multipole methods on graphical processor units (GPUs). Our
two-dimensional double precision code features an
asymmetric type of adaptive space discretization leading to
a particularly elegant and flexible implementation. All
steps of the multipole algorithm are efficiently performed
on the GPU, including the initial phase which assembles the
topological information of the input data. Through careful
timing experiments we investigate the effects of the
various peculiarities with the GPU architecture.}
}
@TechReport{ it:2012-011,
author = {Martins da Silva, Margarida and Torbj{\"o}rn Wigren and
Teresa Mendonca},
title = {An Adaptive Controller for Propofol in Anesthesia under
Synergistic Remifentanil Disturbances},
institution = it,
department = syscon,
year = 2012,
number = {2012-011},
month = may,
abstract = {An adaptive controller for propofol administration relying
on a minimally parameterized SISO Wiener model for the
depth of anesthesia is proposed. The exact linearization of
this minimal Wiener structure using the continuous-time
model parameters estimated online by an extended Kalman
filter is a key point in the design. A linear quadratic
Gaussian controller is developed for the exactly linearized
system. The depth of anesthesia is considered to be
measured by the bispectral index. Excellent results were
obtained when the robustness of the proposed controller
with respect to inter and intrapatient variability was
assessed through simulations on a database of 500 patients.
The closed-loop system showed good disturbance rejection
properties when the synergistic effect of remifentanil in
the depth of anesthesia was considered.}
}
@TechReport{ it:2012-010,
author = {Muneeb Khan and Nikos Nikoleris and Erik Hagersten},
title = {Investigating How Simple Software Optimizations Effect
Relative Throughput Scaling on Multicores},
institution = it,
department = docs,
year = 2012,
number = {2012-010},
month = may,
abstract = {Optimizing applications for off-chip bandwidth usage has
become increasingly critical as computing resources in
multicore processors have increased much faster than shared
resources, off-chip bandwidth and shared cache capacity.
While improved use of shared resources can benefit single
core performance, it is crucial for system with several
active cores, where the way each core uses shared resources
can directly impact the performance of sibling cores.
Although optimizing for memory bandwidth has been a
priority for decades, the tools to effectively profile
application memory accesses are relatively new. With such
tools we can uncover memory accesses that use shared cache
capacity and memory bandwidth inefficiently, and trace them
back to the original source code. This paper presents case
studies of using memory access profiles to uncover and
explain critical memory access issues for three selected
workloads. These memory bottlenecks are resolved using
commonly applicable software optimization techniques. We
then investigate the throughput wall $-$ the relationship
between the drop in off-chip traffic, post-optimization,
and the resulting throughput gain achieved. Our experiments
for multi-execution show that, after optimization, the drop
in off-chip traffic is reflected in the maximum throughput
that can be achieved by the optimized workloads relative to
the original.}
}
@TechReport{ it:2012-009,
author = {Petia Boyanova and Maya Neytcheva},
title = {Efficient Numerical Solution of Discrete Multi-Component
{C}ahn-{H}illiard Systems},
institution = it,
department = tdb,
year = 2012,
number = {2012-009},
month = apr,
abstract = {In this work we develop preconditioners for the iterative
solution of the large scale algebraic systems, arising in
finite element discretizations of microstructures with an
arbitrary number of components, described by the diffusive
interface model. The suggested numerical techniques are
applied to the study of ternary fluid flow processes.}
}
@TechReport{ it:2012-008,
author = {Kenneth Duru and Gunilla Kreiss},
title = {Numerical Interaction of Boundary Waves with Perfectly
Matched Layers in Elastic Waveguides},
institution = it,
department = tdb,
year = 2012,
number = {2012-008},
month = apr,
abstract = {Perfectly matched layers (PML) are a novel technique to
simulate the absorption of waves in open domains. Wave
propagation in isotropic elastic waveguides has the
possibility to support propagating modes with negative
group velocities and long wavelengths. Propagating modes
with negative group velocities can lead to temporally
growing solutions in the PML. In this paper, we demonstrate
that negative group velocities in isotropic elastic
waveguides are not harmful to the discrete PML. Analysis
and numerical experiments confirm the accuracy and the
stability of the PML.}
}
@TechReport{ it:2012-007,
author = {Kenneth Duru and Gunilla Kreiss},
title = {Boundary Waves and Stability of the Perfectly Matched
Layer},
institution = it,
department = tdb,
year = 2012,
number = {2012-007},
month = apr,
abstract = {We study the stability of the perfectly matched layer
(PML) for symmetric second order hyperbolic partial
differential equations on the upper half plane, with
boundary conditions at $y = 0$. Using a mode analysis, we
develop a technique to analyze the stability of the
corresponding initial boundary value problem on the half
plane. We apply our technique to the PML for the elastic
wave equations subject to free surface and homogenous
Dirichlet boundary conditions, and to the PML for the
curl--curl Maxwell's equation subject to insulated walls
and perfectly conducting walls boundary conditions. The
conclusion is that these half--plane problems do not
support temporally modes.}
}
@TechReport{ it:2012-006,
author = {Johanna Bj{\"o}rklund and Eric J{\"o}nsson and Lisa Kaati},
title = {Aspects of Plan Operators in a Tree Automata Framework},
institution = it,
year = 2012,
number = {2012-006},
month = apr,
abstract = {Plan recognition addresses the problem of inferring an
agents goals from its action. Applications range from
anticipating care-takers' needs to predicting volatile
situations. In this contribution, we describe a prototype
plan recognition system that is based on the
well-researched theory of (weighted) finite tree automata.
To illustrate the system?s capabilities, we use data
gathered from matches in the real-time strategy game
StarCraft II. Finally, we discuss how more advanced plan
operators can be accommodated for in this framework while
retaining computational efficiency by taking after the
field of formal model checking and over-approximating the
target language.}
}
@TechReport{ it:2012-005,
author = {Stefan Engblom},
title = {On the Stability of Stochastic Jump Kinetics},
institution = it,
department = tdb,
year = 2012,
number = {2012-005},
month = feb,
abstract = {Motivated by the lack of a suitable framework for
analyzing popular stochastic models of Systems Biology, we
devise conditions for existence and uniqueness of solutions
to certain jump stochastic differential equations (jump
SDEs). Working from simple examples we find
\emph{reasonable} and \emph{explicit} assumptions on the
driving coefficients for the SDE representation to make
sense. By `reasonable' we mean that stronger assumptions
generally do not hold for systems of practical interest. In
particular, we argue against the traditional use of global
Lipschitz conditions and certain common growth
restrictions. By `explicit', finally, we like to highlight
the fact that the various constants occurring among our
assumptions \emph{all can be determined once the model is
fixed}.
We show how basic perturbation results can be derived in
this setting such that these can readily be compared with
the corresponding estimates from deterministic dynamics.
The main complication is that the natural path-wise
representation is generated by a counting measure with an
intensity that depends nonlinearly on the state.}
}
@TechReport{ it:2012-004,
author = {Jens Berg and Jan Nordstr{\"o}m},
title = {Superconvergent Functional Output for Time-Dependent
Problems using Finite Differences on Summation-By-Parts
Form},
institution = it,
department = tdb,
year = 2012,
number = {2012-004},
month = feb,
abstract = {Finite difference operators satisfying the
summation-by-parts (SBP) rules can be used to obtain high
order accurate, energy stable schemes for time-dependent
partial differential equations, when the boundary
conditions are imposed weakly by the simultaneous
approximation term (SAT).
In general, an SBP-SAT discretization is accurate of order
p+1 with an internal accuracy of 2p and a boundary accuracy
of p. Despite this, it is shown in this paper that any
linear functional computed from the time-dependent
solution, will be accurate of order 2p when the boundary
terms are imposed in a stable and dual consistent way.
The method does not involve the solution of the dual
equations, and superconvergent functionals are obtained at
no extra computational cost. Four representative model
problems are analyzed in terms of convergence and errors,
and it is shown in a systematic way how to derive schemes
which gives superconvergent functional outputs.}
}
@TechReport{ it:2012-003,
author = {David Ekl{\"o}v and Nikos Nikoleris and David
Black-Schaffer and Erik Hagersten},
title = {Design and Evaluation of the {B}andwidth {B}andit},
institution = it,
department = docs,
year = 2012,
number = {2012-003},
month = feb,
abstract = {Applications that are co-scheduled on a multicore compete
for shared resources, such as cache capacity and memory
bandwidth. The performance degradation resulting from this
contention can be substantial, which makes it important to
effectively manage these shared resources. This, however,
requires an understanding of how applications are impacted
by such contention.
While the effects of contention for cache capacity have
been extensively studied, less is known about the effects
of contention for memory bandwidth. This is in large due to
its complex nature, as sensitivity to bandwidth contention
depends on bottlenecks at several levels of the
memory-system, the interaction and locality properties of
the application~s access stream. This paper explores the
contention effects of increased latency and decreased
memory parallelism at different points in the memory
hierarchy, both of which cause decreases in available
bandwidth. To understand the impact of such contention on
applications, it also presents a method whereby an
application~s overall sensitivity to different degrees of
bandwidth contention can be directly measured. This method
is used to demonstrate the varying contention sensitivity
across a selection of benchmarks, and explains why some of
them experience substantial slowdowns long before the
overall memory bandwidth saturates. }
}
@TechReport{ it:2012-002,
author = {O. Axelsson and P. Boyanova and M. Kronbichler and M.
Neytcheva and X. Wu},
title = {Numerical and Computational Efficiency of Solvers for
Two-Phase Problems},
institution = it,
department = tdb,
year = 2012,
number = {2012-002},
month = jan,
abstract = {We consider two-phase flow problems, modelled by the
Cahn-Hilliard equation. In our work, the nonlinear
fourth-order equation is decomposed into a system of two
second-order equations for the concentration and the
chemical potential.
We analyse solution methods based on an approximate
two-by-two block factorization of the Jacobian of the
nonlinear discrete problem. We propose a preconditioning
technique that reduces the problem of solving the
non-symmetric discrete Cahn-Hilliard system to the problem
of solving systems with symmetric positive definite
matrices where off-the-shelf multilevel and multigrid
algorithms are directly applicable. The resulting solution
methods exhibit optimal convergence and computational
complexity properties and are suitable for parallel
implementation.
We illustrate the efficiency of the proposed methods by
various numerical experiments, including parallel results
for large scale three dimensional problems.}
}
@TechReport{ it:2012-001,
author = {Magnus Gustafsson and James Demmel and Sverker Holmgren},
title = {Numerical Evaluation of the Communication-Avoiding
{L}anczos Algorithm},
institution = it,
department = tdb,
year = 2012,
number = {2012-001},
month = jan,
abstract = {The Lanczos algorithm is widely used for solving large
sparse symmetric eigenvalue problems when only a few
eigenvalues from the spectrum are needed. Due to sparse
matrix-vector multiplications and frequent synchronization,
the algorithm is communication intensive leading to poor
performance on parallel computers and modern cache-based
processors. The Communication-Avoiding Lanczos algorithm
[Hoemmen; 2010] attempts to improve performance by taking
the equivalence of $s$ steps of the original algorithm at a
time. The scheme is equivalent to the original algorithm in
exact arithmetic but as the value of $s$ grows larger,
numerical roundoff errors are expected to have a greater
impact. In this paper, we investigate the numerical
properties of the Communication-Avoiding Lanczos
(CA-Lanczos) algorithm and how well it works in practical
computations. Apart from the algorithm itself, we have
implemented techniques that are commonly used with the
Lanczos algorithm to improve its numerical performance,
such as semi-orthogonal schemes and restarting. We present
results that show that CA-Lanczos is often as accurate as
the original algorithm. In many cases, if the parameters of
the $s$-step basis are chosen appropriately, the numerical
behaviour of CA-Lanczos is close to the standard algorithm
even though it is somewhat more sensitive to loosing mutual
orthogonality among the basis vectors.}
}
@TechReport{ it:2011-032,
author = {Bj{\"o}rn Halvarsson and Torsten Wik and Bengt Carlsson},
title = {New Input-Output Pairing Strategies Based on Linear
Quadratic {G}aussian Control},
institution = it,
department = syscon,
year = 2011,
number = {2011-032},
month = dec,
abstract = {Two input-output pairing strategies based on linear
quadratic Gaussian (LQG) control are suggested. In the
first strategy, denoted linear quadratic interaction index
(LQII), input-output pairing suggestions are found from a
minimization of the output signal variance. This index not
only guides to what pairing should be tried, it also gives
a direct measure of how much better a full MIMO controller
can perform. The second proposed interaction measure,
denoted integrating linear quadratic index array (ILQIA),
focuses more on the low frequency behaviour of the
considered plant, such as load disturbances. The strategies
are used to compare the expected performance of
decentralized control structures in some illustrative
examples. The pairing suggestions are compared with the
recommendations previously obtained using other interaction
measures such as the relative gain array (RGA), the Hankel
interaction index array (HIIA) and the participation matrix
(PM). The new strategies are easy to interpret and give
suitable pairing recommendations where other methods may
fail.}
}
@TechReport{ it:2011-031,
author = {H{\aa}kan Selg},
title = {Om nya kontaktm{\"o}nster i arbetslivet: {F}acebook,
{L}inked{I}n, {T}witter},
institution = it,
department = mdi,
year = 2011,
number = {2011-031},
month = dec,
note = {In Swedish.},
abstract = {Under senare {\aa}r har telefoni och e-post kompletterats
med nya digitala kontaktverktyg; SMS, och direktmeddelanden
("chatt"), sociala medier som Facebook och LinkedIn och
mikrobloggen Twitter. F{\"o}r r{\"o}stsamtal finns numera
ocks{\aa} IP-telefoni. I en pilotstudie fr{\aa}n 2010
framkom att nya kontaktm{\"o}nster h{\aa}ller p{\aa} att
etableras i sp{\aa}ren av de nya verktygen. I syfte att
kartl{\"a}gga anv{\"a}ndningen av de olika verktygen
genomf{\"o}rdes under mars 2011 en
enk{\"a}tunders{\"o}kning bland Dataf{\"o}reningens
medlemmar.
Resultaten av digitala kontaktverktyg redovisas i tv{\aa}
rapporter; en redan publicerad som behandlar kontaktverktyg
f{\"o}r en eller ett f{\aa}tal mottagare och den
f{\"o}religgande som tar upp verktyg som riktar sig till
ett st{\"o}rre antal mottagare.
Sociala medier har n{\aa}tt stort genomslag i den
unders{\"o}kta gruppen d{\"a}r de allra flesta har skaffat
konton p{\aa} b{\aa}de Facebook och LinkedIn. M{\"o}nstren
i anv{\"a}ndningen skiljer sig d{\"a}remot {\aa}t.
F{\"o}r en majoritet anv{\"a}ndarna {\"a}r Facebook ett
verktyg f{\"o}r kontakter och utbyte av information som
{\"a}r relaterat till privatsf{\"a}ren."V{\"a}nkretsen"
p{\aa} Facebook domineras av privata kontakter men med
inslag av personer med koppling till yrkeslivet. Kvinnor
anv{\"a}nder Facebook mer {\"a}n vad m{\"a}n g{\"o}r. En
h{\"o}gre andel kvinnor har konto p{\aa} Facebook, har fler
v{\"a}nner och l{\"a}ser oftare av sitt konto och g{\"o}r
egna bidrag och statusuppdateringar.
P{\aa} LinkedIn dominerar ist{\"a}llet professionella
"connections". Yrkesrelaterade inl{\"a}gg och
statusuppdateringar {\"a}r i klar majoritet. F{\"o}r de
allra flesta handlar det om ett passivt engagemang.
{\AA}tskilliga dagar f{\"o}rflyter mellan bes{\"o}ken och
{\"a}nnu fler mellan statusuppdateringarna. En mindre grupp
utnyttjar dock LinkedIn som plattform f{\"o}r diskussioner
i professionella angel{\"a}genheter. P{\aa} LinkedIn {\"a}r
m{\"a}nnen mera aktiva {\"a}n kvinnorna vad g{\"a}ller
s{\aa}v{\"a}l bes{\"o}k som statusuppdateringar.
Twitter visar sig inte ha mycket gemensamt med Facebook och
LinkedIn. Endast var fj{\"a}rde av de tillfr{\aa}gade har
skaffat sig konto. Det finns en k{\"a}rna av engagerade
twittrare {\"a}ven om majoriteten {\"a}r mer eller mindre
passiva. M{\aa}nga av dem som skaffat konto verkar
os{\"a}kra om vad det ska anv{\"a}ndas till.
Id{\'e}n om sociala medier som plattformar och fora f{\"o}r
aktivt informationsutbyte och diskussion f{\aa}r bara
delvis st{\"o}d i materialet. Det dominerande intrycket
{\"a}r att ett f{\"o}rh{\aa}llandevis begr{\"a}nsat antal anv{\"a}ndare svarar f{\"o}r merparten av inl{\"a}ggen.}
}
@TechReport{ it:2011-030,
author = {P. Boyanova and I. Georgiev and S. Margenov and L.
Zikatanov},
title = {Multilevel Preconditioning of Graph-{L}aplacians:
Polynomial Approximation of the Pivot Blocks Inverses},
institution = it,
department = tdb,
year = 2011,
number = {2011-030},
month = nov,
abstract = {We consider the discrete system resulting from mixed
finite element approximation of a second-order elliptic
boundary value problem with Crouzeix-Raviart non-conforming
elements for the vector valued unknown function and
piece-wise constants for the scalar valued unknown
function. Since the mass matrix corresponding to the vector
valued variables is diagonal, these unknowns can be
eliminated exactly. Thus, the problem of designing an
efficient algorithm for the solution of the resulting
algebraic system is reduced to one of constructing an
efficient algorithm for a system whose matrix is a
graph-Laplacian (or weighted graph-Laplacian).
We propose a preconditioner based on an algebraic
multilevel iterations (AMLI) algorithm. The hierarchical
two-level transformations and the corresponding $2\times 2$
block splittings of the graph-Laplacian needed in an AMLI
algorithm are introduced locally on macroelements. Each
macroelement is associated with an edge of a coarser
triangulation. To define the action of the preconditioner
we employ polynomial approximations of the inverses of the
pivot blocks in the $2\times 2$ splittings. Such
approximations are obtained via the best polynomial
approximation of $x^{-1}$ in $L_{\infty}$ norm on a finite
interval. Our construction provides sufficient accuracy and
moreover, guarantees that each pivot block is approximated
by a positive definite matrix polynomial.
One possible application of the constructed efficient
preconditioner is in the numerical solution of unsteady
Navier-Stokes equations by a projection method. It can also
be used to design efficient solvers for problems
corresponding to other mixed finite element discretizations.}
}
@TechReport{ it:2011-029,
author = {Alberto Ros and Stefanos Kaxiras},
title = {{VIPS}: Simple Directory-Less Broadcast-Less Cache
Coherence Protocol},
institution = it,
department = docs,
year = 2011,
number = {2011-029},
month = nov,
abstract = {Coherence in multicores introduces complexity and overhead
(directory, state bits) in exchange for local caching,
while being ``invisible'' to the memory consistency model.
In this paper we show that a much simpler
(directory-less/broadcast-less) multicore coherence
provides almost the same performance without the complexity
and overhead of a directory protocol. Motivated by recent
efforts to simplify coherence for disciplined parallelism,
we propose a hardware approach that does not require any
application guidance. The cornerstone of our approach is a
run-time, application-transparent, division of data into
private and shared at a page-level granularity. This allows
us to implement a dynamic write-policy (write-back for
private, write-through for shared), simplifying the
protocol to just two stable states. Self-invalidation of
the shared data at synchronization points allows us to
remove the directory (and invalidations) completely, with
just a data-race-free guarantee (at the write-through
granularity) from software. Allowing multiple simultaneous
writers and merging their writes, relaxes the DRF guarantee
to a word granularity and optimizes traffic. This leads to
our main result: a virtually costless coherence that uses
the same simple protocol for both shared, DRF data and
private data (differentiating only in the timing of when to
put data back in the last-level cache) while at the same
time approaching the performance (within 3\%) of a complex
directory protocol. }
}
@TechReport{ it:2011-028,
author = {Gunnika Isaksson-Luttemann and Bengt Sandblad and Arne W.
Andersson and Simon Tchirner},
title = {Reducing Unnecessary Cognitive Load in Traffic Control},
institution = it,
department = hci,
year = 2011,
number = {2011-028},
month = nov,
abstract = {Uppsala University has collaborated with Swedish National
Railway Administration in research about train traffic
control and how to improve traffic controllers' work
environment, so that they can better meet future demands.
This has resulted in a new operational train traffic
control system called STEG. The traffic controllers are
today forced to develop and use very complex mental models
which take a long time to learn. We have also found that
their cognitive capacity is more used to indentify,
understand and analyze the traffic situation and less to
solve problems and find optimal solutions to disturbances.
The objective for developing STEG was to change this
situation and reduce unnecessary cognitive load. Interviews
with traffic controllers show that STEG has reduced the
complexity of their mental models and contributed to less
unnecessary cognitive load in operation. Our conclusion is
that by reducing the complexity of their mental model, they
can be skilled much faster and they are now able to use
their cognitive capacity and skills on the important parts
of their work. }
}
@TechReport{ it:2011-027,
author = {Gunnika Isaksson-Lutteman and Arvid Kauppi and Arne W
Andersson and Bengt Sandblad and Mikael Erlandsson},
title = {Operative Tests of a New System for Train Traffic
Control},
institution = it,
department = hci,
year = 2011,
number = {2011-027},
month = nov,
abstract = {Tomorrow's train traffic systems requires new strategies
and solutions for efficient train traffic control and
utilization of track capacity, especially in traffic
systems with a high degree of deregulated and mixed
traffic. There are many different goals associated with the
traffic control tasks and the work of the traffic
controllers (dispatchers). Examples are safety, efficiency
of the traffic with regard to timeliness and energy
consumption, good service and information to passengers and
customers etc. Today's traffic control systems and user
interfaces do not efficiently support such goals.
In earlier research we have analyzed important aspects of
the traffic controller's tasks, strategies, decision
making, use of information and support systems etc. Based
on this research we, together with Banverket (Swedish Rail
Administration), have designed prototype systems and
interfaces that better can meet future goals and contribute
to more optimal use of infrastructure capacity.}
}
@TechReport{ it:2011-026,
author = {Martin Kronbichler and Gunilla Kreiss},
title = {A Hybrid Level-Set-Phase-Field Method for Two-Phase Flow
with Contact Lines},
institution = it,
department = tdb,
year = 2011,
number = {2011-026},
month = dec,
abstract = {We present a hybrid method combining a level set model
with a phase field model. Contact line dynamics are
represented by the full phase field model, whereas the
convective interface transport and the evaluation of
surface tension in the bulk of the domain are realized by a
conservative level set model. This combination avoids the
singularity at the contact line that is present in
classical level set models with no-slip boundary
conditions. The hybrid method relies on the similar shape
of the concentration variable in the phase field model and
the level set function. The terms specific to the phase
field model are disabled away from the contact region by
using a switch function. The benefits of using the level
set model instead of the phase field model in the bulk of
the domain are quantified by two extensive numerical
benchmark computations. The conservative level set method
gives considerably higher accuracy at the same mesh size
than the phase field method. For the phase field method, a
range of interface thicknesses and the mobilities are
considered. The best values of these parameters for the two
test cases are used in the comparison. Further, the
well-posedness and stability of the hybrid method are shown
using an a priori energy estimate. Numerical simulation of
channel flow with the hybrid method demonstrates the
increase in computational efficiency compared to a plain
phase field model.}
}
@TechReport{ it:2011-025,
author = {Martin Kronbichler and Katharina Kormann},
title = {A Generic Interface for Parallel Cell-Based Finite Element
Operator Application},
institution = it,
department = tdb,
year = 2011,
number = {2011-025},
month = nov,
abstract = {We present a memory-efficient and parallel framework for
finite element operator application implemented in the
generic open-source library deal.II. Instead of assembling
a sparse matrix and using it for matrix-vector products,
the operation is applied by cell-wise quadrature. The
evaluation of shape functions is implemented with a
sum-factorization approach. Our implementation is
parallelized on three levels to exploit modern
supercomputer architecture in an optimal way: MPI over
remote nodes, thread parallelization with dynamic task
scheduling within the nodes, and explicit vectorization for
utilizing processors' vector units. Special data structures
are designed for high performance and to keep the memory
requirements to a minimum. The framework handles adaptively
refined meshes and systems of partial differential
equations. We provide performance tests for both linear and
nonlinear PDEs which show that our cell-based
implementation is faster than sparse matrix-vector products
for polynomial order two and higher on hexahedral elements
and yields ten times higher Gflops rates.}
}
@TechReport{ it:2011-024,
author = {Martin Kronbichler and Claudio Walker and Gunilla Kreiss
and Bernhard M{\"u}ller },
title = {Multiscale Modeling of Capillary-Driven Contact Line
Dynamics},
institution = it,
department = tdb,
year = 2011,
number = {2011-024},
month = nov,
abstract = {We present a multiscale method to simulate the flow of two
immiscible incompressible fluids in contact with solids.
The macro model in our method is based on a level set
method with sharp interface treatment. The contact line is
tracked explicitly and moves according to a slip velocity
that depends on the apparent contact angle of the interface
with the solid. The relation between apparent contact angle
and slip velocity is determined in a micro model based on
the phase field method. The phase field method seeks for an
equilibrium slip velocity in a box around the contact
point, given a static contact angle at the solid and the
apparent contact angle in the far field. The dimensions of
the box are chosen in the range of physical diffusion
length scales at the contact point. We present numerical
results of the multiscale method for capillary-driven flows
which demonstrate the convergence of results in the macro
model and compare the behavior with other approaches in
contact line dynamics. }
}
@TechReport{ it:2011-023,
author = {Hossein Bani-Hashemian and Stefan Hellander and Per
L{\"o}tstedt},
title = {Efficient Sampling in Event-Driven Algorithms for
Reaction-Diffusion Processes},
institution = it,
department = tdb,
year = 2011,
number = {2011-023},
month = oct,
abstract = {In event-driven algorithms for simulation of diffusing,
colliding, and reacting particles, new positions and events
are sampled from the cumulative distribution function (CDF)
of a probability distribution. The distribution is sampled
frequently and it is important for the efficiency of the
algorithm that the sampling is fast. The CDF is known
analytically or computed numerically. Analytical formulas
are sometimes rather complicated making them difficult to
evaluate. The CDF may be stored in a table for
interpolation or computed directly when it is needed.
Different alternatives are compared for chemically reacting
molecules moving by Brownian diffusion in two and three
dimensions. The best strategy depends on the dimension of
the problem, the length of the time interval, the density
of the particles, and the number of different reactions.}
}
@TechReport{ it:2011-022,
author = {Magnus Gustafsson and Anna Nissen and Katharina Kormann},
title = {Stable Difference Methods for Block-Structured Adaptive
Grids},
institution = it,
department = tdb,
year = 2011,
number = {2011-022},
month = oct,
abstract = {The time-dependent Schrödinger equation describes quantum
dynamical phenomena. Solving it numerically, the
small-scale interactions that are modeled require very fine
spatial resolution. At the same time, the solutions are
localized and confined to small regions in space. Using the
required resolution over the entire high-dimensional domain
often makes the model problems intractable due to the
prohibitively large grids that result from such a
discretization. In this paper, we present a
block-structured adaptive mesh refinement scheme, aiming at
efficient adaptive discretization of high-dimensional
partial differential equations such as the time-dependent
Schrödinger equation. Our framework allows for anisotropic
grid refinement in order to avoid unnecessary refinement.
For spatial discretization, we use standard finite
difference stencils together with summation-by-parts
operators and simultaneous-approximation-term interface
treatment. We propagate in time using exponential
integration with the Lanczos method. Our theoretical and
numerical results show that our adaptive scheme is stable
for long time integrations. We also show that the
discretizations meet the expected convergence rates.}
}
@TechReport{ it:2011-021,
author = {H{\aa}kan Selg},
title = {Om nya kontaktm{\"o}nster i arbetslivet: {SMS}, chatt,
e-post och telefoni - N{\"a}r anv{\"a}nds vad?},
institution = it,
department = hci,
year = 2011,
number = {2011-021},
month = oct,
note = {In Swedish.},
abstract = {Under senare {\aa}r har telefoni och e-post kompletterats
med nya digitala kontaktverktyg; SMS, och direktmeddelanden
("chatt"), sociala medier som Facebook och LinkedIn och
mikrobloggen Twitter. F{\"o}r r{\"o}stsamtal finns numera
ocks{\aa} IP-telefoni. I en pilotstudie fr{\aa}n 2010
framkom att nya kontaktm{\"o}nster h{\aa}ller p{\aa} att
etableras i sp{\aa}ren av de nya verktygen. I syfte att
kartl{\"a}gga anv{\"a}ndningen av de olika verktygen
genomf{\"o}rdes under mars 2011 en
enk{\"a}tunders{\"o}kning bland Dataf{\"o}reningens
medlemmar.
Den h{\"a}r rapporten behandlar kontaktverktygen f{\"o}r en
eller ett f{\aa}tal mottagare och d{\"a}r det huvudsakliga
syftet med kontakten {\"a}r dialog. I en kommande rapport
behandlas sociala medier, dvs. kommunikation med ett
st{\"o}rre antal utvalda mottagare.
Resultaten pekar mot ett relativt specialiserat
kontaktm{\"o}nster i yrkesrelaterade sammanhang d{\"a}r
e-post och mobiltelefoni utg{\"o}r standardverktygen
f{\"o}r text- respektive r{\"o}stmeddelanden. De {\"o}vriga
verktygen uppvisar av st{\"o}rre variation i
anv{\"a}ndarm{\"o}nstren. Anv{\"a}ndningen av
direktmeddelanden {\"a}r p{\aa} v{\"a}g upp{\aa}t och har
redan passerat fast telefoni f{\"o}r yrkesrelaterade
kontakter. H{\"a}r dominerar de yngre anv{\"a}ndarna.
Den privata anv{\"a}ndningen k{\"a}nnetecknas dels av en
bredare repertoar i valet av kontaktverktyg, dels tydligare
tendenser i anv{\"a}ndarm{\"o}nstren. SMS och
direktmeddelanden utnyttjas mer av kvinnor {\"a}n av
m{\"a}n. Vidare ger {\aa}ldersfaktorn ett starkare utslag
vid privat anv{\"a}ndning. Slutsatsen blir d{\"a}rf{\"o}r
att anv{\"a}ndarm{\"o}nstren vid privata kontakter
utm{\"a}rks av st{\"o}rre heterogenitet.
Anv{\"a}ndningen av fast telefoni minskar successivt.
Tendensen {\"a}r generell men processen sker snabbare i
arbetslivet. I likhet med chatten m{\"a}rks en
{\aa}ldersrelaterad tendens men med omv{\"a}nda
f{\"o}rtecken. Yngre anv{\"a}ndare {\"o}verger i st{\"o}rre
utstr{\"a}ckning den fasta telefonin.
De tillfr{\aa}gade ombads rangordna de olika
kontaktverktygens l{\"a}mplighet vid ett antal givna
situationer. Det visade sig d{\aa} att telefonsamtalet,
oavsett det sker via fast, mobil eller IP-telefoni, rankas
h{\"o}gt i alla situationer. Lika popul{\"a}r i
yrkessammanhang {\"a}r e-posten som dessutom har den
f{\"o}rdelen att kontakten dokumenteras. Detta {\"a}r
framf{\"o}r allt uppskattat n{\"a}r syftet {\"a}r att
tr{\"a}ffa en {\"o}verenskommelse. S{\aa}v{\"a}l SMS som
direktmeddelanden bed{\"o}ms l{\"a}mpliga vid informella
situationer och i kontakter med personer man k{\"a}nner
v{\"a}l. Vid br{\aa}dskande {\"a}renden rankas SMS som
n{\"a}st b{\"a}sta alternativet efter telefonsamtal.
Valet av kontaktverktyg p{\aa}verkas i liten grad av om
kontakten sker i yrket eller i privata sammanhang. Mer
styrande {\"a}r andra omst{\"a}ndigheter , t.ex. om
kontakten {\"a}r av formell eller informell natur eller om
{\"a}rendet {\"a}r br{\aa}dskande. St{\"o}rst roll spelar
hur pass v{\"a}l man k{\"a}nner personen som ska kontaktas, inbegripet vilka kontaktverktyg hon eller han k{\"a}nner sig hemmastadd med.}
}
@TechReport{ it:2011-020,
author = {Natasha Flyer and Erik Lehto and S{\'e}bastien Blaise and
Grady B. Wright and Amik St-Cyr},
title = {{RBF}-Generated Finite Differences for Nonlinear Transport
on a Sphere: Shallow Water Simulations},
institution = it,
department = tdb,
year = 2011,
number = {2011-020},
month = sep,
abstract = {The current paper establishes the computational efficiency
and accuracy of the RBF-FD method for large-scale
geoscience modeling with comparisons to state-of-the-art
methods as high-order discontinuous Galerkin and spherical
harmonics, the latter using expansions with close to
300,000 bases. The test cases are demanding fluid flow
problems on the sphere that exhibit numerical challenges,
such as Gibbs phenomena, sharp gradients, and complex
vortical dynamics with rapid energy transfer from large to
small scales over short time periods. The computations were
possible as well as very competitive due to the
implementation of hyperviscosity on large RBF stencil sizes
(corresponding roughly to 6th to 9th order methods) with up
to O($10^5$) nodes on the sphere. The RBF-FD method scaled
as O($N$) per time step, where $N$ is the total number of
nodes on the sphere.}
}
@TechReport{ it:2011-019,
author = {Qaisar Abbas and Jan Nordstr{\"o}m},
title = {A Weak Boundary Procedure for High Order Finite Difference
Approximations of Hyperbolic Problems},
institution = it,
department = tdb,
year = 2011,
number = {2011-019},
month = sep,
abstract = {We introduce a new weak boundary procedures for high order
finite difference operators on summation-by-parts type
applied to hyperbolic problems. The boundary procedure is
applied in an extended domain where data is known. We show
how to raise the order of accuracy for a diagonal norm
based approximation and how to modify the spectrum of the
resulting operator to get a faster convergence to
steady-state. Furthermore, we also show how to construct
better non-reflecting properties at the boundaries using
the above procedure. Numerical results that corroborate the
analysis are presented.}
}
@TechReport{ it:2011-018,
author = {Magnus Johansson and Bj{\"o}rn Victor and Joachim Parrow},
title = {Computing Strong and Weak Bisimulations for Psi-Calculi --
with proofs},
institution = it,
department = csd,
year = 2011,
number = {2011-018},
month = aug,
abstract = {We present a symbolic transition system and strong and
weak bisimulation equivalences for psi-calculi, and show
that they are fully abstract with respect to bisimulation
congruences in the non-symbolic semantics. A procedure
which computes the most general constraint under which two
agents are bisimilar is developed and proved correct.
A psi-calculus is an extension of the pi-calculus with
nominal data types for data structures and for logical
assertions representing facts about data. These can be
transmitted between processes and their names can be
statically scoped using the standard pi-calculus mechanism
to allow for scope migrations. Psi-calculi can be more
general than other proposed extensions of the pi-calculus
such as the applied pi-calculus, the spi-calculus, the
fusion calculus, or the concurrent constraint pi-calculus.
Symbolic semantics are necessary for an efficient
implementation of the calculus in automated tools exploring
state spaces, and the full abstraction property means the
symbolic semantics makes exactly the same distinctions as
the original. }
}
@TechReport{ it:2011-017,
author = {Anna Nissen and Gunilla Kreiss and Margot Gerritsen},
title = {Stability at Nonconforming Grid Interfaces for a High
Order Discretization of the {S}chr{\"o}dinger Equation},
institution = it,
department = tdb,
year = 2011,
number = {2011-017},
month = aug,
note = {Typos corrected October 7, 2011.},
abstract = {In this paper we extend the results from our earlier work
on stable boundary closures for the Schr{\"o}dinger
equation using the summation-by-parts-simultaneous
approximation term (SBP--SAT) method to include stability
and accuracy at non-conforming grid interfaces. Stability
at the grid interface is shown by the energy method, and
the estimates are generalized to multiple dimensions. The
accuracy of the grid interface coupling is investigated
using normal mode analysis for operators of 2nd and 4th
order formal interior accuracy. We show that full accuracy
is retained for the 2nd and 4th order operators. The
accuracy results are extended to 6th and 8th order
operators by numerical simulations, in which case two
orders of accuracy is gained with respect to the lower
order approximation close to the interface.}
}
@TechReport{ it:2011-016,
author = {Elena Sundkvist and Elisabeth Larsson},
title = {Implementation of a Collocated Boundary Element Method for
Acoustic Wave Propagation in Multilayered Fluid Media},
institution = it,
year = 2011,
number = {2011-016},
month = jun,
abstract = {The numerical solution of the Helmholtz equation with
nonlocal radiation boundary conditions is considered. We
model sound wave propagation in a multilayered piecewise
homogeneous medium. A fourth-order accurate collocated,
boundary element method is used, where the solution inside
the domain is computed through a representation integral.
The method is shown to have the expected fourth-order
convergence and is also compared with a fourth-order
accurate finite difference method. }
}
@TechReport{ it:2011-015,
author = {Elena Sundkvist and Kurt Otto},
title = {Discretization of a Hybrid Model for Acoustic Wave
Propagation in Layered Fluid Media},
institution = it,
department = tdb,
year = 2011,
number = {2011-015},
month = jun,
abstract = {The objective is to construct and discretize (to
fourth-order accuracy) a hybrid model for waveguide
problems, where a finite difference method for
inhomogeneous layers is coupled to a boundary element
method (BEM) for a set of homogeneous layers. Such a hybrid
model is adequate for underwater acoustics in complicated
environments. Waveguides with either plane or axial
symmetry are treated, which leads to (algebraically)
two-dimensional problems. The main focus is on the
collocated BEM.},
note = {Updated 2011-08-08.}
}
@TechReport{ it:2011-014,
author = {Anna Nissen and Gunilla Kreiss and Margot Gerritsen},
title = {High Order Stable Finite Difference Methods for the
{S}chr{\"o}dinger Equation},
institution = it,
department = tdb,
year = 2011,
number = {2011-014},
month = may,
abstract = {In this paper we extend the
Summation-by-parts-simultaneous approximation term
(SBP-SAT) technique to the Schr{\"o}dinger equation.
Stability estimates are derived and the accuracy of
numerical approximations of interior order 2m, m=1, 2, 3,
are analyzed in the case of Dirichlet boundary conditions.
We show that a boundary closure of the numerical
approximations of order m lead to global accuracy of order
m+2. The results are supported by numerical simulations.}
}
@TechReport{ it:2011-013,
author = {Hans Norlander},
title = {On the Impact of Model Accuracy for Active Damping of a
Viscoelastic Beam},
institution = it,
department = syscon,
year = 2011,
number = {2011-013},
month = may,
abstract = {How much do model errors influence the closed loop
performance? This question is investigated for the control
problem of designing active damping of vibrations in a
viscoelastic cantilever beam. The beam is physically
modeled using Fourier transformed Euler-Bernoulli beam
equations. For control design the standard LQG technique is
employed, and two different finite order models are used.
One is based on truncated modal analysis of the system, and
the other model is numerically fitted with respect to the
frequency response of the physically theoretical model. The
so obtained controllers are evaluated on the physical model
with respect to disturbance attenuation and robustness for
stability. It is found that all controllers stabilizes the
system and attenuates the vibrations, but the controllers
based on the numerically fitted model perform notably
better than those based on truncated modal analysis.}
}
@TechReport{ it:2011-012,
author = {Jens Lindstr{\"o}m and Jan Nordstr{\"o}m},
title = {Stable {R}obin Boundary Conditions for the
{N}avier-{S}tokes Equations},
institution = it,
department = tdb,
year = 2011,
number = {2011-012},
month = apr,
abstract = {In this paper we prove stability of Robin solid wall
boundary conditions for the compressible Navier-Stokes
equations. Applications include the no-slip boundary
conditions with prescribed temperature or temperature
gradient and the first order slip-flow boundary conditions.
The formulation is uniform and the transitions between
different boundary conditions are done by a change of
parameters. We give different sharp energy estimates
depending on the choice of parameters.
The discretization is done using finite differences on
Summation-By-Parts form with weak boundary conditions using
the Simultaneous Approximation Term. We verify convergence
by the method of manufactured solutions and show
computations of flows ranging from no-slip to substantial
slip.}
}
@TechReport{ it:2011-011,
author = {Petia Boyanova and Minh Do-Quang and Maya Neytcheva},
title = {Efficient Preconditioners for Large Scale Binary
{C}ahn-{H}illiard Models},
institution = it,
department = tdb,
year = 2011,
number = {2011-011},
month = apr,
abstract = {Abstract: In this work we consider preconditioned
iterative solution methods for numerical simulations of
multiphase flow problems, modelled by the Cahn-Hilliard
equation. We focus on diphasic flows and the construction
and efficiency of a preconditioner for the algebraic
systems arising from finite element discretizations in
space and the $\theta$-method in time. The preconditioner
utilizes to a full extent the algebraic structure of the
underlying matrices and exhibits optimal convergence and
computational complexity properties. Large scale umerical
experiments are included as well as performance comparisons
with other solution methods. }
}
@TechReport{ it:2011-010,
author = {Linda {\AA}mand},
title = {Control of Aeration Systems in Activated Sludge Plants - a
review},
institution = it,
department = syscon,
year = 2011,
number = {2011-010},
month = apr,
abstract = {This review attempts to summarise and categorise research
performed within the field of control of continuous
aeration systems in municipal wastewater treatment plants
over the last ten years. The review covers research into
various methods to both decide and track the dissolved
oxygen set-point but also the control of the total aerated
volume. With respect to dissolved oxygen set-point control
and determination, the strategies used for control span
from modifications and developments of simple control
methods that have been explored since the 1970's, to
advanced control such as model-based predictive and
feedback controllers. Also, fuzzy logic control has gained
more interest in the control of continuous processes and is
utilised both in the context of deciding and tracking
set-points, but also to control the total aerobic volume.
The review is supplemented by a discussion on what level of
complexity is required for an aeration control system
together with a summary of comparisons between control
strategies evaluated in full-scale, pilot scale and in
simulations.}
}
@TechReport{ it:2011-009,
author = {Owe Axelsson and Maya Neytcheva},
title = {Operator Splittings for Solving Nonlinear, Coupled
Multiphysics Problems with an Application to the Numerical
Solution of an Interface Problem},
institution = it,
department = tdb,
year = 2011,
number = {2011-009},
month = apr,
abstract = {This work summarizes operator splitting methods to solve
various kinds of coupled multiphysics problems. Such
coupled problems are usually stiff. Furthermore, one is
often interested in obtaining stationary solutions, which
require integration over long time intervals. Therefore, an
implicit and stable time-stepping method of at least second
order of accuracy must be used, to allow for larger
timesteps. To control the operator splitting errors for
nonlinear problems, an approximate Newton solution method
is proposed for each separate equation. After completion of
some (normally few) Newton steps, the equations are updated
with the current solution, thereby preparing for the next
sequence of Newton steps.
An application for a nonlinear model of interface tracking
problem arising in a multiphase flow is described. Hereby
an inner--outer iterative solution method with a proper
preconditioning for solving the arising linearized
algebraic equations, which results in few iterations, is
analyzed. There is no need to update the preconditioner
during the iterations.}
}
@TechReport{ it:2011-008,
author = {Kenneth Duru and Ken Mattsson and Gunilla Kreiss},
title = {Stable and Conservative Time Propagators for Second Order
Hyperbolic Systems},
institution = it,
department = tdb,
year = 2011,
number = {2011-008},
month = apr,
abstract = {In this paper we construct a hierarchy of arbitrary high
(even) order accurate explicit time propagators for
semi-discrete second order hyperbolic systems. An accurate
semi-discrete problem is obtained by approximating the
corresponding spatial derivatives using high order accurate
finite difference operators satisfying the summation by
parts rule. In order to obtain a strictly stable
semi-discrete problem, boundary conditions are imposed
weakly using the simultaneous approximation term method.
The time discretization starts with a second order central
difference scheme, then using the modified equation
approach (even in the presence of a first order derivative
in time) we derive arbitrary high order accurate time
marching schemes. For the fully discrete problem, we
introduce a suitable weighted inner product and use the
energy method to derive an optimal CFL condition, which
provides a useful and rigorous criterion for stability.
Numerical examples are also provided. }
}
@TechReport{ it:2011-007,
author = {Vasileios Spiliopoulos and Stefanos Kaxiras and Georgios
Keramidas},
title = {A Framework for Continuously Adaptive {DVFS}},
institution = it,
department = docs,
year = 2011,
number = {2011-007},
month = mar,
abstract = {We present Continuously Adaptive Dynamic Voltage-Frequency
Scaling in Linux systems running on Intel i7 and AMD Phenom
II processors. By exploiting slack, inherent in
memory-bound programs, our approach aims to improve power
efficiency even when the processor does not sit idle. Our
underlying methodology is based on a simple first-order
processor performance model in which frequency scaling is
expressed as a change (in cycles) of the main memory
latency. Utilizing available performance monitoring
hardware, we show that our model is powerful enough to i)
predict with reasonable accuracy the effect of frequency
scaling (in terms of performance loss), and ii) predict the
energy consumed by the core under different V/f
combinations. To validate our approach we perform
high-accuracy, fine-grain, power measurements directly on
the off-chip voltage regulators. We use our model to
implement various DVFS policies as Linux ~green~ governors
to continuously optimize for various power- efficiency
metrics such as EDP (Energy-Delay Product) or ED2P
(Energy-Delay-Square Product), or achieve energy savings
with a user-specified limit on performance loss. Our
evaluation shows that, for SPEC2006 workloads, our
governors achieve dynamically the same optimal EDP or ED2P
(within 2\% on average) as an exhaustive search of all
possible frequencies and supply voltages. Energy savings
can reach up to 56\% in memory-bound workloads with
corresponding improvements of about 55\% for EDP or ED2P. }
}
@TechReport{ it:2011-006,
author = {Xin He and Maya Neytcheva},
title = {Preconditioning the Incompressible {N}avier-{S}tokes
Equations with Variable Viscosity},
institution = it,
department = tdb,
year = 2011,
number = {2011-006},
month = mar,
note = {Updated April 5, 2011.},
abstract = {This paper deals with preconditioners for the iterative
solution of the discrete Oseen's problem with variable
viscosity. The motivation of this work originates from
numerical simulations of multiphase flow, governed by the
coupled Cahn-Hilliard and incompressible Navier-Stokes
equations. The impact of variable viscosity on some known
preconditioning technique is analyzed. Numerical
experiments show that the preconditioning technique for the
Oseen's problem with constant viscosity is also efficient
when the viscosity is varying.}
}
@TechReport{ it:2011-005,
author = {Andreas Hellander and Stefan Hellander and Per
L{\"o}tstedt},
title = {Coupled Mesoscopic and Microscopic Simulation of
Stochastic Reaction-Diffusion Processes in Mixed
Dimensions},
institution = it,
department = tdb,
year = 2011,
number = {2011-005},
abstract = {We present a new simulation algorithm that allows for
dynamic switching between a mesoscopic and a microscopic
modeling framework for stochastic reaction-diffusion
kinetics. The more expensive and more accurate microscopic
model is used only for those species and in those regions
in space where there is reason to believe that a
microscopic model is needed to capture the dynamics
correctly. The microscopic algorithm is extended to
simulation on curved surfaces in order to model reaction
and diffusion on membranes. The accuracy of the method on
and near a spherical membrane is analyzed and evaluated in
a numerical experiment. Two biologically motivated examples
are simulated in which the need for microscopic simulation
of parts of the system arises for different reasons. First,
we apply the method to a model of the phosphorylation
reactions in a MAPK signaling cascade where microscale
methods are necessary to resolve fast rebinding events.
Then a model is considered for transport of a species over
a membrane coupled to reactions in the bulk. The new
algorithm attains an accuracy similar to a full microscopic
simulation by handling critical interactions on the
microscale, but at a significantly reduced cost by using
the mesoscale framework for most parts of the biological
model.}
}
@TechReport{ it:2011-004,
author = {Petia Boyanova and Minh Do-Quang and Maya Neytcheva},
title = {Solution Methods for the {C}ahn-{H}illiard Equation
Discretized by Conforming and Non-Conforming Finite
Elements},
institution = it,
department = tdb,
year = 2011,
number = {2011-004},
month = mar,
abstract = {In this work we consider preconditioned iterative solution
methods for numerical simulations of multiphase flow
problems, modelled by the Cahn-Hilliard equation. We focus
on the construction and efficiency of various
preconditioning techniques and the effect of two
discretization methods - conforming and non-conforming
finite elements spaces - on those techniques.}
}
@TechReport{ it:2011-003,
author = {Brian Drawert and Stefan Engblom and Andreas Hellander},
title = {{URDME} v. 1.1: User's manual},
institution = it,
department = tdb,
year = 2011,
number = {2011-003},
month = mar,
note = {The latest version of URDME can be obtained from
\url{www.urdme.org}. For earlier versions of URDME consult
Technical Report 2008-022.},
abstract = {We have developed URDME, a general software for simulation
of stochastic reaction-diffusion processes on unstructured
meshes. This allows for a more flexible handling of
complicated geometries and curved boundaries compared to
simulations on structured, cartesian meshes. The underlying
algorithm is the next subvolume method (NSM), extended to
unstructured meshes by obtaining jump coefficients from the
finite element formulation of the corresponding macroscopic
equation. This manual describes the changes in the software
compared to the previous version, URDME 1.0. Notable
changes include support for Comsol Multiphysics 3.5a and a
stronger decoupling between core simulation routines and
the Matlab interface by making core solvers stand-alone
executables. This opens up for more flexible simulation
workflows when many realizations of the stochastic process
need to be generated.}
}
@TechReport{ it:2011-002,
author = {Johannes Nygren and Bengt Carlsson},
title = {Benchmark Simulation Model no. 1 with a Wireless Sensor
Network for Monitoring and Control},
institution = it,
department = syscon,
year = 2011,
number = {2011-002},
month = jan,
abstract = {The implementation of wireless sensor networks (WSNs) for
wastewater treatment plant monitoring and control is rare
in the literature. Nevertheless, there seem to be some good
reasons for considering this application, since WSNs can
easily supply several point measurements and keep track on
a single variable over a wide area. This report describes a
merged simulator, which is a fusion between a SimuLink
implementation of Benchmark Simulation Model no. 1 (BSM1)
and Prowler (a probabilistic WSN simulator). This makes it
possible to simulate the relevant aspects of a WSN and the
effects of implementing it for automatic control of a
wastewater treatment plant. Also, a simple energy model is
added to keep track on the WSN energy consumption.}
}
@TechReport{ it:2010-031,
author = {Bengt Carlsson},
title = {Constant is Optimal - a Strategy for Resource Efficient
Control of a Class of Processes},
institution = it,
department = syscon,
year = 2010,
number = {2010-031},
month = dec,
abstract = {In this technical report we consider the problem on how to
control a class of processes in a resource/energy optimal
way. The optimization is done under the constraint that the
mean value of the output signal (typically an effluent
discharge) should be below a certain threshold. A key
assumption is that the magnitude of the control signal is
proportional to the quantity that should be minimized (for
example, consumption of energy or chemicals) and that the
process efficiency decreases with increasing magnitude of
the control signal. We show that for a wide class of
processes it is optimal to keep the input signal constant.
The result is illustrated in a simple numerical example. }
}
@TechReport{ it:2010-030,
author = {Jens Lindstr{\"o}m and Jan Nordstr{\"o}m},
title = {Spectral Analysis of the Continuous and Discretized Heat
and Advection Equation on Single and Multiple Domains},
institution = it,
department = tdb,
year = 2010,
number = {2010-030},
month = dec,
abstract = {In this paper we study the heat and advection equation in
single and multiple domains. We discretize using a second
order accurate finite difference method on
Summation-By-Parts form with weak boundary and interface
conditions. We derive analytic expressions for the spectrum
of the continuous problem and for their corresponding
discretization matrices. We show how the spectrum of the
single domain operator is contained in the multi domain
operator spectrum when artificial interfaces are
introduced. We study the impact on the spectrum and
discretization errors depending on the interface treatment
and verify that the results are carried over to higher
order accurate schemes.}
}
@TechReport{ it:2010-029,
author = {Owe Axelsson and Maya Neytcheva},
title = {A General Approach to Analyse Preconditioners for
Two-by-Two Block Matrices},
institution = it,
department = tdb,
year = 2010,
number = {2010-029},
month = nov,
abstract = {Two-by-two block matrices arise in various applications,
such as in domain decomposition methods or, more generally,
when solving boundary value problems discretized by finite
elements from the separation of the node set of the mesh
into 'fine' and 'coarse' nodes. Matrices with such a
structure, in saddle point form arise also in mixed
variable finite element methods and in constrained
optimization problems.
A general algebraic approach to construct, analyse and
control the accuracy of preconditioners for matrices in
two-by-two block form is presented. This includes both
symmetric and nonsymmetric matrices, as well as indefinite
matrices. The action of the preconditioners can involve
element-by-element approximations and/or geometric or
algebraic multigrid/multilevel methods.}
}
@TechReport{ it:2010-028,
author = {H{\aa}kan Selg},
title = {Om professionell anv{\"a}ndning av sociala medier och
andra digitala kanaler},
institution = it,
department = hci,
year = 2010,
number = {2010-028},
month = nov,
abstract = {Ny teknik i kombination med sociala processer st{\"a}ller
dagens ledare inf{\"o}r en rad utmaningar. Inneh{\aa}llet i
rapporten baseras p{\aa} 20 expertsamtal d{\"a}r
experternas erfarenheter och intressen varit styrande.
Resultatet har blivit en bred {\"o}versikt som dels kan
tj{\"a}na som utg{\aa}ngspunkt f{\"o}r f{\"o}rdjupade
studier, dels som ett aktuellt diskussionsunderlag f{\"o}r
personer inom ber{\"o}rda verksamheter.}
}
@TechReport{ it:2010-027,
author = {Arnold Pears and Carsten Schulte},
title = {Proceedings of the 9th Koli Calling International
Conference on Computing Education Research},
institution = it,
department = docs,
year = 2010,
number = {2010-027},
month = nov,
note = {Typographical updates 2010-11-25.},
abstract = {The 9th Koli Calling conference collected together
reseachers from Europe, the United States and Asia-Pacific
to discuss and present research which contributes to a
richer education for students of computing worldwide.
Working versions of the papers to presented are distributed
before the conference and authors revise and resubmit their
papers after the conference, incorporating input from
conference discussions. These final versions are published
in this volume, and represent the final output of the 2009
conference. Happy reading! }
}
@TechReport{ it:2010-026,
author = {Xin He and Maya Neytcheva and Stefano Serra Capizzano},
title = {On an Augmented {L}agrangian-Based Preconditioning of
{O}seen Type Problems},
institution = it,
department = tdb,
year = 2010,
number = {2010-026},
month = nov,
abstract = {The paper deals with a general framework for constructing
preconditioners for saddle point matrices, in particular as
arising in the discrete linearized Navier-Stokes equations
(Oseen's problem). We utilize the so-called augmented
Lagrangian approach, where the original linear system of
equations is first transformed to an equivalent one, which
latter is then solved by a preconditioned iterative
solution method.
The matrices in the linear systems, arising after the
discretization of Oseen's problem, are of two-by-two block
form as are the best known preconditioners for these. In
the augmented Lagrangian formulation, a scalar
regularization parameter is involved, which strongly
influences the quality of the block-preconditioners for the
system matrix (referred to as 'outer'), as well as the
conditioning and the solution of systems with the resulting
pivot block (referred to as 'inner') which, in the case of
large scale numerical simulations has also to be solved
using an iterative method. We analyse the impact of the
value of the regularization parameter on the convergence of
both outer and inner solution methods.
The particular preconditioner used in this work exploits
the inverse of the pressure mass matrix. We study the
effect of various approximations of that inverse on the
performance of the preconditioners, in particular that of a
sparse approximate inverse, computed in an
element-by-element fashion. We analyse and compare the
spectra of the preconditioned matrices for the different
approximations and show that the resulting preconditioner
is independent of problem, discretization and method
parameters, namely, viscosity, mesh size, mesh anisotropy.
We also discuss possible approaches to solve the modified
pivot matrix block.}
}
@TechReport{ it:2010-025,
author = {Soma Tayamon and Torbj{\"o}rn Wigren},
title = {Recursive Identification and Scaling of Non-linear Systems
using Midpoint Numerical Integration},
institution = it,
department = syscon,
year = 2010,
number = {2010-025},
month = oct,
abstract = {A new recursive prediction error algorithm (RPEM) based on
a non- linear ordinary differential equation (ODE) model of
black-box state space form is presented. The selected model
is discretised by a midpoint inte- gration algorithm and
compared to an Euler forward algorithm. When the algorithm
is applied, scaling of the sampling time is used to improve
performance further. This affects the state vector, the
parameter vector and the Hessian. This impact is analysed
and described in three Theorems. Numerical examples are
provided to verify the theoretical results obtained.}
}
@TechReport{ it:2010-024,
author = {Elias Rudberg and Emanuel H. Rubensson},
title = {Assessment of Density Matrix Methods for Electronic
Structure Calculations},
institution = it,
department = tdb,
year = 2010,
number = {2010-024},
month = oct,
abstract = {Purification and minimization methods for computation of
the one-particle density matrix are compared. This is done
by considering the work needed by each method to achieve a
given accuracy in terms of the difference to the exact
solution. Simulations employing orthogonal as well as
non-orthogonal versions of the methods are performed using
both element magnitude and cutoff radius based truncation
approaches. The results indicate that purification is
considerably more efficient than the studied minimization
methods even when a good starting guess for minimization is
available. The computational cost of the studied
minimization methods is observed to be significantly more
sensitive to small band gaps than purification. An
$\mathcal{O}(\sqrt{1/\xi})$ dependence on the band gap
$\xi$ is observed for minimization which can be compared to
the $\mathcal{O}(\ln{(1/\xi)})$ dependence for
purification. Minimization is found to perform at its best
at 50\% occupancy. Error control and stopping criteria are
also discussed.}
}
@TechReport{ it:2010-023,
author = {Ken Mattsson},
title = {Summation by Parts Operators for Finite Difference
Approximations of Second-Derivatives with Variable
Coefficients},
institution = it,
department = tdb,
year = 2010,
number = {2010-023},
month = oct,
abstract = {Finite difference operators approximating second
derivatives with variable coefficients and satisfying a
summation-by-parts rule have been derived for the second-,
fourth- and sixth-order case by using the symbolic
mathematics software Maple. The operators are based on the
same norms as the corresponding approximations of the first
derivate, which makes the construction of stable
approximations to general multi-dimensional
hyperbolic-parabolic problems straightforward.}
}
@TechReport{ it:2010-022,
author = {Torbj{\"o}rn Wigren and Linda Brus and Soma Tayamon},
title = {{MATLAB} Software for Recursive Identification and Scaling
Using a Structured Nonlinear Black-box Model - Revision 6},
institution = it,
department = syscon,
year = 2010,
number = {2010-022},
month = sep,
note = {Revised version of nr 2010-002. The software package can
be downloaded from
\url{http://www.it.uu.se/research/publications/reports/2010-022/NRISSoftwareRev6.zip}.}
,
abstract = {This report is intended as a users manual for a package of
MATLAB scripts and functions, developed for recursive
prediction error identification of nonlinear state space
systems and nonlinear static systems. The core of the
package is an implementation of related output error
identification and scaling algorithms. The algorithms are
based on a continuous time, structured black box state
space model of a nonlinear system. Furthermore, to
initialize the algorithm an initiation scheme based on
Kalman filter theory is included. The purpose of the
initialization algorithm is to find initial parameters for
the prediction error algorithm, and thus reducing the risk
of convergence to local false minima. An RPEM algorithm for
recursive identification of nonlinear static systems, that
re-uses the parameterization of the nonlinear ODE model, is
also included in the software package. In this version of
the software a new discretization of the continuous time
model based on the midpoint integration algorithm is added.
The software can only be run off-line, i.e. no true real
time operation is possible. The algorithms are however
implemented so that true on-line operation can be obtained
by extraction of the main algorithmic loop. The user must
then provide the real time environment. The software
package contains scripts and functions that allow the user
to either input live measurements or to generate test data
by simulation. The scripts and functions for the setup and
execution of the identification algorithms are somewhat
more general than what is described in the references.
There is e.g. support for automatic re-initiation of the
algorithms using the parameters obtained at the end of a
previous identification run. This allows for multiple runs
through a set of data, something that is useful for data
sets that are too short to allow convergence in a single
run. The re-initiation step also allows the user to modify
the degrees of the polynomial model structure and to
specify terms that are to be excluded from the model. This
makes it possible to iteratively re-fine the estimated
model using multiple runs. The functionality for display of
results include scripts for plotting of data, parameters,
prediction errors, eigenvalues and the condition number of
the Hessian. The estimated model obtained at the end of a
run can be simulated and the model output plotted, alone or
together with the data used for identification. Model
validation is supported by two methods apart from the
display functionality. First, a calculation of the RPEM
loss function can be performed, using parameters obtained
at the end of an identification run. Secondly, the accuracy
as a function of the output signal amplitude can be
assessed.}
}
@TechReport{ it:2010-021,
author = {Michael Thun{\'e} and Anna Eckerdal},
title = {Students' Conceptions of Computer Programming},
institution = it,
department = tdb,
year = 2010,
number = {2010-021},
month = sep,
note = {The phenomenographic outcome space presented in this
report has previously been published as part of a journal
article (Thun{\'e} and Eckerdal 2009). Due to space
limitations in the journal publication, we have found it
appropriate to make available a more comprehensive
description of the outcome space, in the present technical
report.},
abstract = {The present work has its focus on university level
engineering education students that do not intend to major
in computer science but still have to take a mandatory
programming course. Phenomenography is applied to empirical
data in the form of semi-structured interviews with
students who had recently taken an introductory programming
course. A phenomenographic outcome space is presented, with
five qualitatively different categories of description of
students~ ways of seeing computer programming.}
}
@TechReport{ it:2010-020,
author = {Torbj{\"o}rn Wigren},
title = {Input-Output Data Sets for Development and Benchmarking in
Nonlinear Identification},
institution = it,
department = syscon,
year = 2010,
number = {2010-020},
month = aug,
note = {The software package can be downloaded from
\url{http://www.it.uu.se/research/publications/reports/2010-020/NonlinearData.zip}}
,
abstract = {This report presents two sets of data, suitable for
development, testing and benchmarking of system
identification algorithms for nonlinear processes. The
first data set is recorded from a laboratory process that
can be well described by a block oriented nonlinear model.
The data set is challenging; it consists of only 500
samples, the nonlinear effect is large and the damping is
not too good. The second data set is recorded from a
laboratory process known to be governed by nonlinear
differential equations.}
}
@TechReport{ it:2010-019,
author = {David Ekl{\"o}v and David Black-Schaffer and Erik
Hagersten},
title = {StatCC: Design and Evaluation},
institution = it,
department = docs,
year = 2010,
number = {2010-019},
month = jun,
abstract = {This work presents StatCC, a simple and efficient model
for estimating the shared cache miss ratios of co-scheduled
applications on architectures with a hierarchy of private
and shared caches. StatCC leverages the StatStack cache
model to estimate the co-scheduled applications' cache miss
ratios from their individual memory reuse distance
distributions, and a simple performance model that
estimates their CPIs based on the shared cache miss ratios.
These methods are combined into a system of equations that
explicitly models the CPIs in terms of the shared miss
ratios and can be solved to determine both. The result is a
fast algorithm with a 2\% error across the SPEC CPU2006
benchmark suite compared to a simulated in-order processor
and a hierarchy of private and shared caches.}
}
@TechReport{ it:2010-018,
author = {Jeremy E. Kozdon and Eric M. Dunham and Jan Nordstr{\"o}m},
title = {Interaction of Waves with Frictional Interfaces Using
Summation-By-Parts Difference Operators, 2. Extension to
Full Elastodynamics},
institution = it,
department = tdb,
year = 2010,
number = {2010-018},
month = jun,
abstract = {Problems in elastodynamics with nonlinear boundary
conditions, such as those arising when modeling earthquake
rupture propagation along internal interfaces (faults)
governed by nonlinear friction laws, are inherently
boundary driven. For such problems, stable and accurate
enforcement of boundary conditions is essential for
obtaining globally accurate numerical solutions (and
predictions of ground motion in earthquake simulations).
High-order finite difference methods are a natural choice
for problems like these involving wave propagation, but
enforcement of boundary conditions is complicated by the
fact that the stencil must transition to one-sided near the
boundary.
In this work we develop a high-order method for tensor
elasticity with faults whose strength is a nonlinear
function of sliding velocity and a set of internal state
variables obeying differential evolution equations (a
mathematical framework known as rate-and-state friction).
The method is based on summation-by-parts finite difference
operators and weak enforcement of boundary conditions using
the simultaneous approximation term method. We prove that
the method is strictly stable and dissipates energy at a
slightly faster rate than the continuous solution (with the
difference in energy dissipation rates vanishing as the
mesh is refined).}
}
@TechReport{ it:2010-017,
author = {Jeremy E. Kozdon and Eric M. Dunham and Jan Nordstr{\"o}m},
title = {Interaction of Waves with Frictional Interfaces Using
Summation-By-Parts Difference Operators, 1. Weak
Enforcement of Nonlinear Boundary Conditions},
institution = it,
department = tdb,
year = 2010,
number = {2010-017},
month = jun,
abstract = {In this work we develop a high-order method for problems
in scalar elastodynamics with nonlinear boundary conditions
in a form closely related to those seen in earthquake
rupture modeling and other frictional sliding problems. By
using summation-by-parts finite difference operators and
weak enforcement of boundary conditions with the
simultaneous approximation term method, a strictly stable
method is developed that dissipates energy at a slightly
faster rate than the continuous solution (with the
difference in energy dissipation rates vanishing as the
mesh is refined). Furthermore, it is shown that unless
boundary conditions are formulated in terms of
characteristic variables, as opposed to the physical
variables in terms of which boundary conditions are more
naturally stated, the semi-discretized system of equations
can become extremely stiff, preventing efficient solution
using explicit time integrators.
These theoretical results are confirmed by several
numerical tests demonstrating the high-order convergence
rate of the method and the benefits of using strictly
stable numerical methods for long time integration. }
}
@TechReport{ it:2010-016,
author = {A. Rensfelt and T. S{\"o}derstr{\"o}m},
title = {Parametric Identification of Complex Modulus},
institution = it,
department = syscon,
year = 2010,
number = {2010-016},
month = jun,
abstract = {This report treats three different approaches to
parametric identification of the complex modulus of a
viscoelastic material. In the first approach, a
nonparametric estimate is used to fit the parametric model,
while in the other two the model is fitted directly from
data. In all three cases, theoretical expressions for the
accuracy of the estimate are derived under the assumption
that the measurement noise is white and that the
signal-to-noise ratio is large. The expressions are
validated against both simulated and experimental data. In
the case of experimental data it is seen that the
theoretical expression severely underestimates the variance
of the identified parameters, and one of the expressions is
therefore modified to cover the case of correlated noise
with much better agreement as a result.}
}
@TechReport{ it:2010-015,
author = {Parosh Aziz Abdulla and Yu-Fang Chen and Giorgio Delzanno
and Fr{\'e}d{\'e}ric Haziza and Chih-Duo Hong and Ahmed
Rezine},
title = {Constrained Monotonic Abstraction: a {CEGAR} for
Parameterized Verification},
institution = it,
department = docs,
year = 2010,
number = {2010-015},
month = jun,
abstract = {In this paper, we develop a counterexample-guided
abstraction refinement (CEGAR) framework for
\emph{monotonic abstraction}, an approach that is
particularly useful in automatic verification of safety
properties for \emph{parameterized systems}. The main
drawback of verification using monotonic abstraction is
that it sometimes generates spurious counterexamples. Our
CEGAR algorithm automatically extracts from each spurious
counterexample a set of configurations called a "Safety
Zone" and uses it to refine the abstract transition system
of the next iteration. We have developed a prototype based
on this idea; and our experimentation shows that the
approach allows to verify many of the examples that cannot
be handled by the original monotonic abstraction approach.}
}
@TechReport{ it:2010-014,
author = {Stefan Hellander and Per L{\"o}tstedt},
title = {Flexible Single Molecule Simulation of Reaction-Diffusion
Processes},
institution = it,
department = tdb,
year = 2010,
number = {2010-014},
month = may,
abstract = {An algorithm is developed for simulation of the motion and
reactions of single molecules at a microscopic level. The
molecules diffuse in a solvent and react with each other or
a polymer and molecules can dissociate. Such simulations
are of interest e.g. in molecular biology. The algorithm is
similar to the Green's function reaction dynamics (GFRD)
algorithm by van Zon and ten Wolde where longer time steps
can be taken by computing the probability density functions
(PDFs) and then sample from its distribution function. Our
computation of the PDFs is much less complicated than GFRD
and more flexible. The solution of the partial differential
equation for the PDF is split into two steps to simplify
the calculations. The sampling is without splitting error
in two of the coordinate directions for a pair of molecules
and a molecule-polymer interaction and is approximate in
the third direction. The PDF is obtained either from an
analytical solution or a numerical discretization. The
errors due to the operator splitting, the partitioning of
the system, and the numerical approximations are analyzed.
The method is applied to three different systems involving
up to four reactions. Comparisons with other mesoscopic and
macroscopic models show excellent agreement. }
}
@TechReport{ it:2010-013,
author = {Jonas Boustedt},
title = {Ways to Understand Class Diagrams},
institution = it,
year = 2010,
number = {2010-013},
month = mar,
note = {Typographic updates 2010-05-04.},
abstract = {The software industry needs well trained software
designers and one important aspect of software design is
the ability to model software designs visually and
understand what visual models represent. However, previous
research indicates that software design is a difficult task
to many students. This paper reports empirical findings
from a phenomenographic investigation on how students
understand class diagrams, UML symbols and relations to
object oriented concepts. The informants were 20 Computer
Science students from four different universities in Sweden.
The results show qualitively different ways to understand
and describe UML class diagrams and the "diamond symbols"
representing aggregation and composition. The purpose of
class diagrams was understood in a varied way, from
describing it as a documentation to a more advanced view
related to communication. The descriptions of class
diagrams varied from seeing them as a specification of
classes to a more advanced view where they were described
to show hierarchic structures of classes and relations. The
diamond symbols were seen as "relations" and a more
advanced way was seeing the white and the black diamonds as
different symbols for aggregation and composition.
As a consequence of the results, it is recommended that UML
should be adopted in courses. It is briefly indicated how
the phenomenographic results in combination with variation
theory can be used by teachers to enhance students'
possibilities to reach advanced understanding of phenomena
related to UML class diagrams. Moreover, it is recommended
that teachers should put more effort in assessing skills in
proper using of the basic symbols and models, and students
should get many opportunities to practise collaborative
design, e.g., using whiteboards.}
}
@TechReport{ it:2010-012,
author = {Jonas Boustedt},
title = {A Student Perspective on Software Development and
Maintenance},
institution = it,
year = 2010,
number = {2010-012},
month = mar,
abstract = {How do Computer Science students view Software Development
and Software Maintenance? To answer this question, a
Phenomenographic perspective was chosen, and 20 Swedish
students at four universities were interviewed.
The interviews were analyzed to find in which different
ways the informants, on collective level, see the phenomena
of interest. The resulting outcome spaces show that
software development is described in a number of
qualitatively different ways reaching from problem solving,
design and deliver, design for the future and then a more
comprehensive view that includes users, customers, budget
and other aspects. Software maintenance is described as
correcting bugs, making additions, adapting to new
requirements from the surroundings, and something that is a
natural part of the job.
Finally, conclusions from the results and additional
observations are discussed in terms of their implications
for teaching, and some suggestions for practical use are
given.}
}
@TechReport{ it:2010-011,
author = {Soma Tayamon and Torbj{\"o}rn Wigren},
title = {Recursive Prediction Error Identification and Scaling of
Non-linear Systems with Midpoint Numerical Integration},
institution = it,
department = syscon,
year = 2010,
number = {2010-011},
month = mar,
abstract = {A new recursive prediction error algorithm (RPEM) based on
a non-linear ordinary differential equation (ODE) model of
black-box state space form is presented. The selected model
is discretised by a midpoint integration algorithm and
compared to an Euler forward algorithm. When the algorithm
is applied, scaling of the sampling time is used to improve
performance further. This affects the state vector, the
parameter vector and the Hessian. This impact is analysed
and described in three Theorems. Numerical examples are
provided to verify the theoretical results obtained.}
}
@TechReport{ it:2010-010,
author = {Maya Neytcheva and Erik B{\"a}ngtsson and Elisabeth
Linn{\'e}r},
title = {Finite-Element Based Sparse Approximate Inverses for
Block-Factorized Preconditioners},
institution = it,
department = tdb,
year = 2010,
number = {2010-010},
month = mar,
abstract = {In this work we analyse a method to construct a
numerically efficient and computationally cheap sparse
approximations of some of the matrix blocks arising in the
block-factorised preconditioners for matrices with a
two-by-two block structure. The matrices arise from finite
element discretizations of partial differential equations.
We consider scalar elliptic problems, however the approach
is appropriate for other types of problems such as
parabolic or systems of equations.
The technique is applicable for both selfadjoint and
non-selfadjoint problems, in two as well as in three
dimensions. We analyze in detail the 2D case and provide
extensive numerical evidence for the efficiency of the
proposed matrix approximations, both serial and parallel.}
}
@TechReport{ it:2010-009,
author = {Salman Toor and Bjarte Mohn and David Cameron and Sverker
Holmgren},
title = {Case-Study for Different Models of Resource Brokering in
Grid Systems},
institution = it,
department = tdb,
year = 2010,
number = {2010-009},
month = mar,
abstract = {To identify the best suitable resource for a given task in
a grid system, under constraints of limited available
information, requires an elaborate strategy. The task gets
even more complicated if the environment is heterogeneous
and the availability of the resources or its information is
not guaranteed for all the time. Efficient and reliable
brokering in grid systems has been discussed extensively,
and different strategies and models have been presented.
However, this issue still needs more attention. In this
paper we first review different brokering models, compare
them and discuss the issues related to them. We have
identify two key areas for improving the resource
allocation: The \textbf{Information Flow} in the system and
the \textbf{Data Awareness} of the resource selection. Our
results show that the better management information flow
between different components in the grid system
significantly improves the efficiency of the resource
allocation process.}
}
@TechReport{ it:2010-008,
author = {Martins da Silva, Margarida and Teresa Mendon\c{c}a and
Torbj{\"o}rn Wigren},
title = {Online Nonlinear Identification of the Effect of Drugs in
Anaesthesia Using a Minimal Parameterization and {BIS}
Measurements},
institution = it,
department = syscon,
year = 2010,
number = {2010-008},
month = mar,
abstract = {This paper addresses the problem of modeling and
identification of the Depth of Anaesthesia (DoA). It
presents a new MISO Wiener model for the pharmacokinetics
and pharmacodynamics of propofol and remifentanil, when
jointly administered to patients undergoing surgery. The
models most commonly used to describe the effect of drugs
in the human body are overparameterized Wiener models. In
particular, in an anaesthesia environment, the high number
of patient-dependent parameters coupled with the
insufficient excitatory pattern of the input signals (drug
dose profiles) and the presence of noise make robust
identification strategies difficult to find. In fact, in
such clinical application the user cannot freely choose the
input signals to enable accurate parameter identification.
A new MISO Wiener model with only four parameters is hence
proposed to model the effect of the joint administration of
the hypnotic propofol and the analgesic remifentanil. An
Extended Kalman Filter (EKF) algorithm was used to perform
the nonlinear online identification of the system
parameters. The results show that both the new model and
the identification strategy outperform the currently used
tools to infer individual patient response. The proposed
DoA identification scheme was evaluated in a real patient
database, where the DoA is quantified by the Bispectral
Index Scale (BIS) measurements. The results obtained so far
indicate that the developed approach will be a powerful
tool for modeling and identification of anaesthetic drug
dynamics during surgical procedures.}
}
@TechReport{ it:2010-007,
author = {Egi Hidayat and Alexander Medvedev},
title = {Parameter Estimation in a Pulsatile Hormone Secretion
Model},
institution = it,
department = syscon,
year = 2010,
number = {2010-007},
month = mar,
abstract = {This paper presents an algorithm to estimate parameters of
a mathematical model of a bipartite endocrine axis.
Secretion of one of the involved hormones is stimulated by
the concentration of another one, called release hormone,
with the latter secreted in a pulsatile manner. The hormone
mechanism in question appears often in animal and human
endocrine systems, i.e. in the regulation of testosterone
in the human male. The model has been introduced elsewhere
and enables the application of the theory of
pulse-modulated feedback control systems to analysis of
pulsatile endocrine regulation. The state-of-the art
methods for hormone secretion analysis could not be applied
here due to different modeling approach. Based on the
mathematical machinery of constrained nonlinear least
squares minimization, a parameter estimation algorithm is
proposed and shown to perform well on actual biological
data yielding accurate fitting of luteinizing hormone
concentration profiles. The performance of the algorithm is
compared with that of state-of-the art techniques and
appears to be good especially in case of undersampled
data.}
}
@TechReport{ it:2010-006,
author = {Carl Nettelblad and Sverker Holmgren},
title = {Stochastically Guaranteed Global Optimums Achievable with
a Divide-and-Conquer Approach to Multidimensional {QTL}
Searches},
institution = it,
department = tdb,
year = 2010,
number = {2010-006},
month = mar,
abstract = {The problem of searching for multiple quantitative trait
loci (QTL) in an experimental cross population of
considerable size poses a significant challenge, if general
interactions are to be considered. Different global
optimization approaches have been suggested, but without an
analysis of the mathematical properties of the objective
function, it is hard to devise reasonable criteria for when
the optimum found in a search is truly global.
We reformulate the standard residual sum of squares
objective function for QTL analysis by a simple
transformation, and show that the transformed function will
be Lipschitz continuous in an infinite-size population,
with a well-defined Lipschitz constant. We discuss the
different deviations possible in an experimental
finite-size population, suggesting a simple bound for the
minimum value found in the vicinity of any point in the
model space.
Using this bound, we modify the DIRECT optimization
algorithm to exclude regions where the optimum cannot be
found according to the bound. This makes the algorithm more
attractive than previously realized, since optimality is
now in practice guaranteed. The consequences are realized
in permutation testing, used to determine the significance
of QTL results. DIRECT previously failed in attaining the
correct thresholds. In addition, the knowledge of a
candidate QTL for which significance is tested allows
spectacular increases in permutation test performance, as
most searches can be abandoned at an early stage.}
}
@TechReport{ it:2010-005,
author = {Carl Nettelblad and {\"O}rjan Carlborg and Jos{\'e} M.
lvarez-Castro},
title = {Assessing Orthogonality and Statical Properties of Linear
Regression Methods for Interval Mapping with Partial
Information},
institution = it,
department = tdb,
year = 2010,
number = {2010-005},
month = mar,
abstract = {\textbf{Background:} Mapping quantitative trait loci (QTL)
has become a widely used tool in genetical research. In
such experiments, it is desired to obtain orthogonal
estimates of genetic effects for a number of reasons
concerning both the biological meaning of the estimated
locations and effects, and making the statistical analysis
clearer and more robust. The currently used statistical
methods, however, are not optimized for orthogonality,
especially in cases involving interval mapping between
markers and/or in incomplete datasets. This is an adverse
limitation for the application of such methods for QTL
scans involving model selection over putative complex gene
networks.
\textbf{Results:} We describe how deviations from
orthogonality arise in currently used methods. We
demonstrate one option for obtaining orthogonal estimates
of genetic effects using multiple imputations per
individual in an otherwise unchanged regression context.
Our proposed IRIM method avoids inflated values for
explainable variance and genetic effect variables, while
showing a clear preference for marker locations in a fine
mapping context. Despite possible shortcomings, similar
results to linear regression are demonstrated for our
proposed approach (IRIM) in an experimental dataset.
\textbf{Conclusions:} Imputation-based methods can be used
to enhance the statistical dissectability of effects, as
well as computational performance. We exemplify how
Haley-Knott regression is not only distorting the
explainable variance, but also point out how the estimated
phenotype values between classes, and the resulting
effects, become dependent. This illustrates the need for a
more radical departure in the approach chosen in order to
achieve orthogonality.}
}
@TechReport{ it:2010-004,
author = {Kenneth Duru and Gunilla Kreiss},
title = {A Well-posed and Discretely Stable Perfectly Matched Layer
for Elastic Wave Equations in Second Order Formulation},
institution = it,
department = tdb,
year = 2010,
number = {2010-004},
month = feb,
abstract = {We present a well-posed and discretely stable perfectly
matched layer for the anisotropic (and isotropic) elastic
wave equations without first re-writing the governing
equations as a first order system. The new model is derived
by the complex coordinate stretching technique. Using
standard perturbation methods we show that complex
frequency shift together with a chosen real scaling factor
ensures the decay of eigen-modes for all relevant
frequencies. To buttress the stability properties and the
robustness of the proposed model, numerical experiments are
presented for anisotropic elastic wave equations. The model
is approximated with a stable node-centered finite
difference scheme that is second order accurate both in
time and space.}
}
@TechReport{ it:2010-003,
author = {Andreas Hellander and Per L{\"o}tstedt},
title = {Incorporating Active Transport of Cellular Cargo in
Stochastic Mesoscopic Models of Living Cells},
institution = it,
department = tdb,
year = 2010,
number = {2010-003},
month = feb,
abstract = {We propose a new multiscale method to incorporate active
transport of cargo particles in biological cells in
stochastic, mesoscopic models of reaction-transport
processes. Given a discretization of the computational
domain, we find stochastic, convective mesoscopic molecular
fluxes over the edges or facets of the subvolumes and
relate the process to a corresponding first order finite
volume discretization of the linear convection equation. We
give an example of how this can be used to model active
transport of cargo particles on a microtubule network by
the motor proteins kinesin and dynein. In this way we
extend mesoscopic reaction-diffusion models of biochemical
reaction networks to more general models of molecular
transport within the living cell.}
}
@TechReport{ it:2010-002,
author = {Torbj{\"o}rn Wigren and Linda Brus and Soma Tayamon},
title = {{MATLAB} Software for Recursive Identification and Scaling
Using a Structured Nonlinear Black-box Model - Revision 5},
institution = it,
department = syscon,
year = 2010,
number = {2010-002},
month = jan,
note = {Revised version of nr 2008-007. The software package can
be downloaded from
\url{http://www.it.uu.se/research/publications/reports/2010-002/NRISSoftwareRev5.zip}.
\textbf{Note} that the software package was updated on
2010-03-16.},
abstract = {This report is intended as a users manual for a package of
MATLAB scripts and functions, developed for recursive
prediction error identification of nonlinear state space
systems and nonlinear static systems. The core of the
package is an implementation of an output error
identification and scaling algorithm. The algorithm is
based on a continuous time, structured black box state
space model of a nonlinear system. Furthermore, to
initialize the algorithm an algorithm based on Kalman
filter theory is included. The purpose of the
initialization algorithm is to find initial parameters for
the prediction error algorithm, and thus reducing the risk
of convergence to local false minima. An RPEM algorithm for
recursive identification of nonlinear static systems, that
re-uses the parameterization of the nonlinear ODE model, is
also included in the software package. In this version of
the software the discretization of the continuous time
model is based on the midpoint integration algorithm. The
software can only be run off-line, i.e. no true real time
operation is possible. The algorithms are however
implemented so that true on-line operation can be obtained
by extraction of the main algorithmic loop. The user must
then provide the real time environment. The software
package contains scripts and functions that allow the user
to either input live measurements or to generate test data
by simulation. The scripts and functions for the setup and
execution of the identification algorithms are somewhat
more general than what is described in the references.
There is e.g. support for automatic re-initiation of the
algorithms using the parameters obtained at the end of a
previous identification run. This allows for multiple runs
through a set of data, something that is useful for data
sets that are too short to allow convergence in a single
run. The re-initiation step also allows the user to modify
the degrees of the polynomial model structure and to
specify terms that are to be excluded from the model. This
makes it possible to iteratively re-fine the estimated
model using multiple runs. The functionality for display of
results include scripts for plotting of data, parameters,
prediction errors, eigenvalues and the condition number of
the Hessian. The estimated model obtained at the end of a
run can be simulated and the model output plotted, alone or
together with the data used for identification. Model
validation is supported by two methods apart from the
display functionality. First, a calculation of the RPEM
loss function can be performed, using parameters obtained
at the end of an identification run. Secondly, the accuracy
as a function of the output signal amplitude can be
assessed.}
}
@TechReport{ it:2010-001,
author = {Mahen Jayawardena and Salman Toor and Sverker Holmgren},
title = {Computational and Visualization tools for Genetic Analysis
of Complex Traits},
institution = it,
department = tdb,
year = 2010,
number = {2010-001},
month = jan,
abstract = {We present grid based tools for simultaneous mapping of
multiple locations (QTL) in the genome that affect
quantitative traits (e.g. body weight, blood pressure) in
experimental populations. The corresponding computational
problem is very computationally intensive. We have earlier
shown that, using appropriate parallelization schemes, this
type of application is suitable for deployment on grid
systems.
A grid portal interface is often an ideal tool for
biologists performing advanced genetic analysis. We
describe an implementation of such a portal system and how
it is used for performing multidimensional QTL searches
efficiently.}
}
@TechReport{ it:2009-027,
author = {Jens Lindstr{\"o}m and Jan Nordstr{\"o}m},
title = {A Stable and High Order Accurate Conjugate Heat Transfer
Problem},
institution = it,
department = tdb,
year = 2009,
number = {2009-027},
month = nov,
abstract = {This paper analyzes well-posedness and stability of a
conjugate heat transfer problem in one space dimension. We
study a model problem for heat transfer between a fluid and
a solid. The energy method is used to derive boundary and
interface conditions that make the continuous problem
well-posed and the semi-discrete problem stable. The
numerical scheme is implemented using 2nd, 3rd and 4th
order finite difference operators on Summation-By-Parts
(SBP) form. The boundary and interface conditions are
implemented weakly. We investigate the spectrum of the
spatial discretization to determine which type of coupling
that gives attractive convergence properties. The rate of
convergence is verified using the method of manufactured
solutions.}
}
@TechReport{ it:2009-026,
author = {Sara Zahedi and Martin Kronbichler and Gunilla Kreiss},
title = {Spurious Currents in a Finite-Element Based Level Set
Method for Two Phase Flow},
institution = it,
department = tdb,
year = 2009,
number = {2009-026},
month = nov,
abstract = {A study of spurious currents in finite element based
simulations of the incompressible Navier-Stokes equations
for two phase flows is presented, based on computations on
a circular drop in equilibrium. The interface is accounted
for by a level set method. It is shown that a sharp surface
tension force, expressed as a line integral along the
interface, can give rise to large spurious currents and
oscillations in the pressure. If instead a regularized
surface tension representation is used, exact force balance
at the interface is possible, both for a fully coupled
discretization approach as well as for a fractional step
projection method. We illustrate that with exact force
balance, the spurious currents are of the order of the
tolerance of the linear solver. However, the numerical
curvature calculation introduces errors, that cause
spurious currents. Different ways to extend the curvature
from the interface to the whole domain are discussed and
investigated. It is shown that the choice of curvature
extension has a significant impact on the error in
pressure. The impact of using different finite element
spaces is also investigated.}
}
@TechReport{ it:2009-025,
author = {Olof Rensfelt and Frederik Hermansand Christofer Ferm and
Per Gunningberg and Lars-{\AA}ke Larzon},
title = {Sensei-{UU}: A Nomadic Sensor Network Testbed Supporting
Mobile Nodes},
institution = it,
department = docs,
year = 2009,
number = {2009-025},
month = oct,
abstract = {We present Sensei - a nomadic, or relocatable, wireless
sensor network (WSN) testbed with support for mobile nodes.
The nomadism makes it possible to evaluate a WSN
application in different environments ranging from lab
environment to in-situ installations to prototype
deployments. Other WSN testbeds are often static and can
not be easily moved between sites.
To be easily relocateable and highly flexible, Sensei uses
a wireless 802.11 b/g network as control channel. Our
design with a wireless control channel allows easy
incorporation of mobile nodes. Since sensor nodes often use
802.15.4 (ZigBee) communication, we have investigated the
interference between the control channel and a 802.15.4 WSN
to ensure that this approach is a feasible approach. For
repeatability in terms of mobility, nodes can be carried
either by humans or robots following mobility scripts.
We present a method for localization of mobile nodes based
on robot technology. The robots use laser range finders for
localization and navigate in a predefined map. We evaluate
the precision of this method in an office like environment
to ensure sufficient repeatability of mobility
experiments.}
}
@TechReport{ it:2009-024,
author = {Iordanis Kavathatzopoulos},
title = {{AvI}-index: A tool to assess usability},
institution = it,
department = hci,
year = 2009,
number = {2009-024},
month = oct,
abstract = {AvI-index is a usability measurement questionnaire to
assess IT systems~ usability as a factor dependent on
efficiency, effectiveness and work environment. It is
focused on how personal skills and organizational processes
contribute to successful user participation and through
that to higher usability, to better work environment, and
to higher effectiveness and efficiency. Reliability
coefficients and correlations to objective criteria were
high confirming the original hypothesis. AvI-index can be
used to acquire information about an IT system~s usability
in an easy and quick way. It can be used to evaluate
interventions and changes of IT systems. It is also a
suitable method to apply continuously over a longer period
of time. Although AvI-index only provides an indicative
value, such a diagnosis of usability in an organization~s
IT infrastructure is valuable as an alert and to determine
the extent of further initiatives. }
}
@TechReport{ it:2009-023,
author = {Martins da Silva, Margarida and Torbj{\"o}rn Wigren and
Teresa Mendonca},
title = {Nonlinear Identification of a Minimal NeuroMuscular
Blockade Model in Anaesthesia},
institution = it,
department = syscon,
year = 2009,
number = {2009-023},
month = sep,
abstract = {The paper presents new modeling and identification
strategies to address the many difficulties in the
identification of anaesthesia dynamics. During general
anaesthesia procedures muscle relaxants are drugs
frequently administered. The most commonly used models for
the effect of such drugs, called NeuroMuscular Blockade
(NMB), comprise a high number (greater than eight) of
pharmacokinetic and pharmacodynamic (PK/PD) parameters. The
main issue concerning the NMB system identification is
that, in the clinical practice, the user cannot freely
choose the system input signals (drug dose profiles to be
administered to the patients) to enable the identification
of such a high number of parameters. The limited amount of
measurement data also indicates a need for new
identification strategies. A new SISO Wiener model with two
parameters is hence proposed to model the effect of the
muscle relaxant atracurium. A batch Prediction Error Method
(PEM) was first developed to optimize the model structure.
Secondly, an Extended Kalman Filter (EKF) approach was used
to perform the online identification of the system
parameters. Both approaches outperform conventional
identification strategies, showing good results regarding
parameter identification and measured signal tracking, when
evaluated on a large patient database. The new methods
proved to be adequate for the description of the system,
even with the poor input signal excitation and the few
measured data samples present in this application. It turns
out that the methods are of general validity for the
identification of drug dynamics in the human body.}
}
@TechReport{ it:2009-022,
author = {Katharina Kormann and Sverker Holmgren and Hans O.
Karlsson},
title = {A {F}ourier-Coefficient Based Solution of an Optimal
Control Problem in Quantum Chemistry},
institution = it,
department = tdb,
year = 2009,
number = {2009-022},
month = sep,
abstract = {We consider an optimal control problem for the
time-dependent Schr{\"o}dinger equation modeling molecular
dynamics. Given a molecule in its ground state, the
interaction with a tuned laser pulse can result in an
excitation to a state of interest. By these means, one can
optimize the yield of chemical reactions. The problem of
designing an optimal laser pulse can be posed as an optimal
control problem. We reformulate the optimization problem by
Fourier-transforming the electric field of the laser and
narrow the frequency band. In this way, we reduce the
dimensionality of the control variable. This allows for
storing an approximate Hessian and, thereby, we can solve
the optimization problem with a quasi-Newton method. Such
an implementation provides superlinear convergence. We show
computational results for a Raman-transition example and
give numerical evidence that our algorithm can outperform
the standard Krotov-like method which does not employ
approximative second derivatives. \end{abstract} }
}
@TechReport{ it:2009-021,
author = {Katharina Kormann and Sverker Holmgren and Hans O.
Karlsson},
title = {Global Error Control of the Time-Propagation for the
{S}chr{\"o}dinger Equation with a Time-Dependent
{H}amiltonian},
institution = it,
department = tdb,
year = 2009,
number = {2009-021},
month = sep,
abstract = {We use a posteriori error estimation theory to derive a
relation between local and global error in the propagation
for the time-dependent Schr\"odinger equation. Based on
this result, we design a class of $h,p$-adaptive
Magnus--Lanczos propagators capable of controlling the
global error of the time-stepping scheme by only solving
the equation once. We provide results for models of several
different small molecules including bounded and
dissociative states, illustrating the efficiency and wide
applicability of the new methods. }
}
@TechReport{ it:2009-020,
author = {Bengt Fornberg and Elisabeth Larsson and Natasha Flyer},
title = {Stable Computations with {G}aussian Radial Basis Functions
in {2-D}},
institution = it,
department = tdb,
year = 2009,
number = {2009-020},
month = aug,
abstract = {Radial basis function (RBF) approximation is an extremely
powerful tool for representing smooth functions in
non-trivial geometries, since the method is meshfree and
can be spectrally accurate. A perceived practical obstacle
is that the interpolation matrix becomes increasingly
ill-conditioned as the RBF shape parameter becomes small,
corresponding to flat RBFs. Two stable approaches that
overcome this problem exist, the Contour-Pad\'e method and
the RBF-QR method. However, the former is limited to small
node sets and the latter has until now only been formulated
for the surface of the sphere. This paper contains an
RBF-QR formulation for planar two-dimensional problems. The
algorithm is perfectly stable for arbitrarily small shape
parameters and can be used for up to a thousand node points
in double precision and for several thousand node points in
quad precision. A sample MATLAB code is provided.}
}
@TechReport{ it:2009-019,
author = {David Ekl{\"o}v and Erik Hagersten},
title = {Statstack: Efficient Modeling of {LRU} Caches},
institution = it,
department = docs,
year = 2009,
number = {2009-019},
month = jul,
abstract = {The identification of the memory gap in terms of the
relatively slow memory accesses put a focus on cache
performance in the 90s. The introduction of the moderately
clocked multicores has shifted this focus from memory
latency to memory bandwidth for modern processors. The
multicore's limited cache capacity per thread in
combination with their current a projected off-chip memory
bandwidth limitation makes this the most likely bottleneck
of future computer systems.
This paper presents a new and efficient way of estimating
the cache performance for an application. The method has
several similarities with that of Stack Distance, but
instead of counting \emph{unique memory objects}, as is
done for Stack Distance calculations, our schema only
requires the \emph{number of memory accesses} to be counted
between two successive accesses to the same data object.
This task can be efficiently handled at runtime by existing
built-in hardware counters. Furthermore, only a small
fraction of the memory accesses have to be monitored for an
accurate estimation.
We show how low-overhead runtime data, similar to that of
StatCache, is sufficient to feed this model. We evaluate
the accuracy of the proposed transformation based on sparse
data and compare the results with that of native stack
distance based all memory accesses. We show excellent
accuracy over a wide range of cache sizes and applications.
}
}
@TechReport{ it:2009-018,
author = {Parosh Aziz Abdulla and Muhsin Atto and Jonathan Cederberg
and Ran Ji},
title = {Automated Analysis of Data-Dependent Programs with Dynamic
Memory},
institution = it,
department = docs,
year = 2009,
number = {2009-018},
month = jun,
abstract = {We present a new approach for automatic verification of
data-dependent programs manipulating dynamic heaps. A heap
is encoded by a graph where the nodes represent the cells,
and the edges reflect the pointer structure between the
cells of the heap. Each cell contains a set of variables
which range over the natural numbers. Our method relies on
standard backward reachability analysis, where the main
idea is to use a simple set of predicates, called
signatures, in order to represent bad sets of heaps.
Examples of bad heaps are those which contain either
garbage, lists which are not well-formed, or lists which
are not sorted. We present the results for the case of
programs with a single next-selector, and where variables
may be compared for (in)equality. This allows us to verify
for instance that a program, like bubble sort or insertion
sort, returns a list which is well-formed and sorted, or
that the merging of two sorted lists is a new sorted list.
We report on the result of running a prototype based on the
method on a number of programs.}
}
@TechReport{ it:2009-017,
author = {Anna Nissen and Gunilla Kreiss},
title = {An Optimized Perfectly Matched Layer for the
{S}chr{\"o}dinger Equation},
institution = it,
department = tdb,
year = 2009,
number = {2009-017},
month = jun,
abstract = {A perfectly matched layer (PML) for the Schr{\"o}dinger
equation using a modal ansatz is presented. We derive
approximate error formulas for the modeling error from the
outer boundary of the PML and for the error from the
discretization and show how these can be matched in order
to obtain optimal performance of the PML. Included
numerical results show that the PML works efficiently at a
prescribed accuracy for the zero potential case, with a
layer of width less than two percent of the computational
domain.}
}
@TechReport{ it:2009-016,
author = {Torsten S{\"o}derstr{\"o}m},
title = {Expressions for the Covariance Matrix of Covariance Data},
institution = it,
department = syscon,
year = 2009,
number = {2009-016},
month = may,
abstract = {In several estimation methods used in system
identification, a first step is to estimate the covariance
functions of the measured inputs and outputs for a small
set of lags. These covariance elements can be set up as a
vector. The report treats the problem of deriving and
computing the asymptotic covariance matrix of this vector,
when the number of underlying input-output data is large.
The derived algorithm is derived under fairly general
assumptions. It is assumed that the input and output are
linked through a linear finite-order system. Further, the
input is assumed to be modelled as an ARMA model of a
fixed, but arbitrary order. Finally, it is allowed that the
both the input and the output are not measured directly,
but with some white measurement noise, thus including
typical errors-in-variables situations in the analysis.}
}
@TechReport{ it:2009-015,
author = {H{\aa}kan Selg},
title = {Tv{\aa} kulturer p{\aa} Internet: Resultat av faktor- och
klusteranalys},
institution = it,
department = hci,
year = 2009,
number = {2009-015},
month = may,
note = {In Swedish.},
abstract = {Bland avancerade anv{\"a}ndare av Internet intar studenter
en nyckelroll. Att studera deras beteenden p{\aa} n{\"a}tet
g{\"o}r det m{\"o}jligt f{\"o}r oss att tidigt uppt{\"a}cka
nya tendenser och att f{\"o}rst{\aa} vad som ligger
framf{\"o}r oss p{\aa} n{\aa}gra {\aa}rs sikt. Vidare
utg{\"o}r studenterna en stor grupp i samh{\"a}llet som
snart kommer att f{\"o}ra sin nyvunna kunskap och sitt
t{\"a}nkande in i arbetslivet. En enk{\"a}t riktad till
studenter, doktorander och anst{\"a}llda vid 32 svenska
universitet och h{\"o}gskolor genomf{\"o}rdes under
h{\"o}sten 2007. Enk{\"a}tsvaren analyserades genom
korstabuleringar, faktoranalys och klusteranalys. Ett
framtr{\"a}dande resultat var att tv{\aa} olika
anv{\"a}ndarm{\"o}nster bland Internetanv{\"a}ndarna
tydligt gick att urskilja. Skillnaden {\"a}r av s{\aa}dan
storlek att vi kan tala om tv{\aa} kulturer. Den ena
kulturen, k{\"a}nnetecknas av env{\"a}gskommunikation, som
att s{\"o}ka information, ta del av nyheter, betala
r{\"a}kningar och best{\"a}lla resor. Kommunikationen
{\"a}r ~vertikal~ och knyter samman f{\"o}retag med sina
kunder, och myndigheter med medborgare. Det dominerande
kommunikationsverktyget {\"a}r e-post. Den andra kulturen
utm{\"a}rks av tv{\aa}v{\"a}gskommunikation d{\"a}r
anv{\"a}ndarna samtidigt {\"a}r konsumenter av information
och producenter av inneh{\aa}ll i n{\"a}tverk. Detta {\"a}r
en v{\"a}rld av n{\"a}tgemenskaper, bloggar och andra
sociala mjukvaror. Kommunikationen {\"a}r ~horisontell~ och
med olika protokoll f{\"o}r \emph{instant messaging} (IM)
som typiskt verktyg f{\"o}r kommunikation.
Rapporten finns {\"a}ven publicerad i Nationellt
IT-anv{\"a}ndarcentrums (NITA) rapportserie fr{\aa}n projektet InternetExplorers som delrapport 9.}
}
@TechReport{ it:2009-014,
author = {Mark H. Carpenter and Jan Nordstr{\"o}m and David
Gottlieb},
title = {Revisiting and Extending Interface Penalties for
Multi-Domain Summation-by-Parts Operators},
institution = it,
department = tdb,
year = 2009,
number = {2009-014},
month = may,
abstract = {A general interface procedure is presented for
multi-domain collocation methods satisfying the
summation-by-parts (SBP) spatial discretization convention.
Unlike more traditional operators (e.g. FEM) applied to the
advection-diffusion equation, the new procedure penalizes
the solution and the first p derivatives across the
interface. The combined interior/interface operators are
proven to be pointwise stable, and conservative, although
accuracy deteriorates for p>=2. Penalties between two
different sets of variables are compared (motivated by FEM
primal and flux formulations), and are shown to be
equivalent for certain choices of penalty parameters.
Extensive validation studies are presented using two
classes of high-order SBP operators: 1) central finite
difference, and 2) Legendre spectral collocation.}
}
@TechReport{ it:2009-013,
author = {Jim Wilenius},
title = {Combinatorial and Simultaneous Auction: A Pragmatic
Approach to Tighter Bounds on Expected Revenue},
institution = it,
department = csd,
year = 2009,
number = {2009-013},
month = may,
note = {Updated May 28, 2009.},
abstract = {It is a common belief that combinatorial auctions provide
good solutions to resource-allocation in multiple-object
markets with synergies. In this work we adopt a pragmatic
approach to examining the revenue bounds on combinatorial
and simultaneous auctions. The theoretical bounds from our
previous work utilize a large number of bidders in order to
show that combinatorial auctions yield a higher expected
revenue. It is reasonable to believe that the true bounds
are much tighter. We argue that this is the indeed the case
and that the first-price combinatorial auction is revenue
superior even when a relatively small number of bidders
participate. The argument is based on three methods. (i)
heuristic equilibrium-strategy search, (ii) sampling of the
expected revenue in the first-price sealed-bid
combinatorial auction, and (iii) a tightened theoretical
upper bound on the sealed-bid simultaneous auction in the
case of few bidders.}
}
@TechReport{ it:2009-012,
author = {Bj{\"o}rn Halvarsson and Bengt Carlsson},
title = {New Input/Output Pairing Strategies based on Minimum
Variance Control and Linear Quadratic Gaussian Control},
institution = it,
department = syscon,
year = 2009,
number = {2009-012},
month = may,
note = {Updated June 2009.},
abstract = {In this paper a new input/output pairing strategy based on
minimum variance control is proposed. A similar version
based on linear quadratic Gaussian (LQG) control is also
suggested. The strategies are used to compare the expected
performance of decentralized control structures in some
illustrative examples. The pairing suggestions are compared
with the recommendations previously obtained using other
interaction measures such as the Relative Gain Array (RGA).
The new strategies give suitable pairing recommendations
and are easy to interpret.}
}
@TechReport{ it:2009-011,
author = {Jan Nordstr{\"o}m and Sofia Eriksson},
title = {Well Posed, Stable and Weakly Coupled Fluid Structure
Interaction Problems},
institution = it,
department = tdb,
year = 2009,
number = {2009-011},
month = apr,
abstract = {We investigate problems of fluid structure interaction
type and aim for a formulation that leads to a well posed
problem and a stable numerical procedure. Our first
objective is to investigate if the generally accepted
formulations of the FSI problems are the only possible ones.
Our second objective is to derive a numerical coupling
which is truly stable. To accomplish that we will use a
weak coupling procedure and employ summation- by-parts
operators and penalty terms. We compare the weak coupling
with other common procedures. We also study the effect of
high order accurate schemes.
In multiple dimensions this is a formidable task and for
that reason we start by investigating the simplest possible
model problem available. As a flow model we use the
linearized Euler equations in one dimension and as the
structure model we consider a spring.}
}
@TechReport{ it:2009-010,
author = {Lars Ferm and Andreas Hellander and Per L{\"o}tstedt},
title = {An Adaptive Algorithm for Simulation of Stochastic
Reaction-Diffusion Processes},
institution = it,
department = tdb,
year = 2009,
number = {2009-010},
month = apr,
abstract = {We propose an adaptive hybrid method suitable for
stochastic simulation of diffusion dominated
reaction-diffusion processes. For such systems, simulation
of the diffusion requires the predominant part of the
computing time. In order to reduce the computational work,
the diffusion in parts of the domain is treated
macroscopically, in other parts with the tau-leap method
and in the remaining parts with Gillespie's stochastic
simulation algorithm (SSA) as implemented in the next
subvolume method (NSM). The chemical reactions are handled
by SSA everywhere in the computational domain. A trajectory
of the process is advanced in time by an operator splitting
technique and the time steps are chosen adaptively. The
spatial adaptation is based on estimates of the errors in
the tau-leap method and the macroscopic diffusion. The
accuracy and efficiency of the method are demonstrated in
examples from molecular biology where the domain is
discretized by unstructured meshes.}
}
@TechReport{ it:2009-009,
author = {Sofia Eriksson and Jan Nordstr{\"o}m},
title = {Analysis of the Order of Accuracy for Node-Centered Finite
Volume Schemes},
institution = it,
department = tdb,
year = 2009,
number = {2009-009},
month = mar,
abstract = {The order of accuracy of the node-centered finite volume
methods is analyzed, and the analysis is based on an exact
derivation of the numerical errors in one dimension. The
accuracy for various types of grids are considered.
Numerical simulations and analysis are performed for both a
hyperbolic and a eliptic case, and the results agree. The
impact of weakly imposed boundary conditions is analyzed
and verified numerically. We show that the error
contribution from the primal and dual grid can be treated
separately.}
}
@TechReport{ it:2009-008,
author = {Henrik Johansson},
title = {A Meta-Partitioner for Run-Time Selection and Evaluation
of Multiple Partitioning Algorithms for {SAMR} Grid
Hierarchies},
institution = it,
department = tdb,
year = 2009,
number = {2009-008},
month = mar,
abstract = {Parallel structured adaptive mesh refinement (SAMR)
methods increase the efficiency of the numerical solution
to partial differential equations. These methods use an
adaptive grid hierarchy to dynamically assign computational
resources to areas with large solution errors. The grid
hierarchy needs to be repeatedly re-partitioned and
distributed over the processors but no single partitioning
algorithm performs well for all hierarchies. This paper
presents an extended and improved version of the
Meta-Partitioner, a partitioning framework that uses the
state of the application to autonomously select, configure,
invoke, and evaluate partitioning algorithms during
run-time. The performance of the partitioning algorithms
are predicted using historical performance data for grid
hierarchies similar to the current hierarchy. At each
re-partitioning, a user-specified number of partitioning
algorithms are selected and invoked. When multiple
partitionings are constructed, the performance of each
partitioning is evaluated during run-time and the best
partitioning is selected. The performance evaluation shows
huge improvements for the two most performance-inhibiting
factors --- the load imbalance and the synchronization
delays. On average, the load imbalance is increased by only
11.5\% and the synchronization delays by 13.6\% compared to
the optimal results from 768 different hybrid partitioning
algorithms.}
}
@TechReport{ it:2009-007,
author = {Henrik Johansson},
title = {Run-Time Selection of Partitioning Algorithms for Parallel
{SAMR} Applications},
institution = it,
department = tdb,
year = 2009,
number = {2009-007},
month = mar,
abstract = {Parallel structured adaptive mesh refinement methods
decrease the execution time and memory requirements of
partial differential equation solvers. These methods result
in an adaptive and dynamic grid hierarchy that repeatedly
needs to be re-partitioned and distributed over the
processors. No single partitioning algorithm can
consistently construct high-quality partitionings for all
possible grid hierarchies. Instead, the partitioning
algorithm needs to be selected during run-time. In this
paper, an initial implementation of the Meta-Partitioner is
presented. At each re-partitioning, the Meta-Partitioner
autonomously selects, configures, and invokes the
partitioning algorithm predicted to result in the best
performance. To predict the performance of the partitioning
algorithms, the Meta-Partitioner uses historic performance
data for grid hierarchies with properties similar to the
current hierarchy. The Meta-Partitioner focuses the
partitioning effort on the most performance-inhibiting
factor --- either the load imbalance or the synchronization
delays. The performance evaluation shows a small but
noticeable performance increase compared to the best static
algorithm. Compared to the average performance for a large
number of partitioning algorithms, the Meta-Partitioner
consistently generates partitionings with a significantly
better performance. }
}
@TechReport{ it:2009-006,
author = {Jan Nordstr{\"o}m and Jing Gong and van der Weide, Edwin
and Magnus Sv{\"a}rd},
title = {A Stable and Conservative High Order Multi-block Method
for the Compressible Navier-Stokes Equations},
institution = it,
department = tdb,
year = 2009,
number = {2009-006},
month = feb,
abstract = {A stable and conservative high order multi-block method
for the time-dependent compressible Navier-Stokes equations
has been developed. Stability and conservation are proved
using summation-by-parts operators, weak interface
conditions and the energy method. This development makes it
possible to exploit the efficiency of the high order finite
difference method for non-trivial geometries. The
computational results corroborate the theoretical
analysis.}
}
@TechReport{ it:2009-005,
author = {Sven-Olof Nystr{\"o}m},
title = {Ideas for a new Erlang},
institution = it,
department = csd,
year = 2009,
number = {2009-005},
month = feb,
abstract = {This paper presents some thoughts and ideas on the future
development of Erlang. Among the topics are: an alternative
to Erlang's selective receive, a simple language mechanism
to allow function in-lining across module boundaries, a new
mechanism for introducing local variables with a more
cleanly defined semantics, and a mini-language to allow the
efficient implementation of low-level algorithms.}
}
@TechReport{ it:2009-004,
author = {Arnold Pears and Lauri Malmi},
title = {The 8th Koli Calling International Conference on Computing
Education Research},
institution = it,
year = 2009,
number = {2009-004},
month = feb,
note = {Updated June 2009.},
abstract = {The contents of this volume are the culmination of nearly
a year of planning and effort on the part of both the local
organising committee and the conference chairs. However, we
were not working alone! Without an active community of
researchers doing quality research and writing papers, a
conference like Koli has no function or purpose.
Consequently, a large part of the success of Koli Calling
lies in its vibrant research community. It is your
submissions that have made it possible for us to select
this year's crop of interesting and thought provoking
contributions.}
}
@TechReport{ it:2009-003,
author = {Erik Nordstr{\"o}m and Per Gunningberg and Christian
Rohner},
title = {A Search-based Network Architecture for Mobile Devices},
institution = it,
department = docs,
year = 2009,
number = {2009-003},
month = jan,
abstract = {This paper presents the Haggle network architecture and
experimental measurements of its performance in a realistic
environment. Haggle provides a search-based data
dissemination framework for mobile opportunistic
communication environments, making it easy to share content
directly between intermittently connected mobile devices.
Haggle's novel approach is based on its identification of
search as a first class operation for data-centric
applications. We show how search can be used for resolution
(mapping data to interested receivers) and prioritization
of sending and receiving data during encounters between
nodes. Haggle provides underlying functionality for
neighbor discovery, resource management and resolution --
thus removing the need to implement such features in
applications.
Haggle has been implemented for several platforms. This
paper presents experimental results, the most interesting
of which demonstrates the live operation of Haggle on
mobile phones in an office environment.}
}
@TechReport{ it:2009-002,
author = {Anna Eckerdal},
title = {Ways of Thinking and Practising in Introductory
Programming},
institution = it,
department = tdb,
year = 2009,
number = {2009-002},
abstract = {In computer programming education it is generally
acknowledged that students learn practical skills and
concepts largely by practising. In addition it is widely
reported that many students face great difficulties in
their learning, despite great efforts during many decades
to improve programming education.
The paper investigates and discusses the relation between
novice computer programming students' conceptual and
practical learning. To this end the present research uses
Ways of Thinking and Practising, WTP as a theoretical
framework. In the present research Thinking is discussed in
terms of students' learning of concepts, while Practising
is discussed as common novice students' programming
activities.
Based on two empirical studies it is argued that there
exists a mutual and complex dependency between conceptual
learning and practise in students' learning process. It is
hard to learn one without the other, and either of them can
become an obstacle that hinders further learning. Empirical
findings point to the need to research the relationship
between conceptual understanding and practise to better
understand students' learning process.
The paper demonstrates a way to research how students'
learning of practise and concepts are related. Results from
a phenomenographic analysis on novice programming students'
understanding of some central concepts are combined with an
analysis based on elements from variation theory of the
students' programming activities. It is shown that
different levels of proficiency in programming activities
as well as qualitatively different levels of conceptual
understandings are related to dimensions of variation. The
dimensions of variation serve as interfaces between the
activities and conceptual understandings. If a dimension is
discerned, this can facilitate coming to richer conceptual
understandings and learning additional activities. }
}
@TechReport{ it:2009-001,
author = {Arne Andersson and Jim Wilenius},
title = {A New Analysis of Revenue in the Combinatorial and
Simultaneous Auction},
institution = it,
department = csd,
year = 2009,
number = {2009-001},
month = jan,
note = {Updated May 2009.},
abstract = {We prove that in many cases, a first-price sealed-bid
combinatorial auction gives higher expected revenue than a
sealed-bid simultaneous auction. This is the first
theoretical evidence that combinatorial auctions indeed
generate higher revenue, which has been a common belief for
decades.
We use a model with many bidders and items, where bidders
are of two types: (i) single-bidders interested in only one
item and (ii) synergy-bidders, each interested in one
random combination of items. We provide an upper bound on
the expected revenue for simultaneous auctions and a lower
bound on combinatorial auctions. Our bounds are
parameterized on the number of bidders and items,
combination size, and synergy.
We derive an asymptotic result, proving that as the number
of bidders approach infinity, expected revenue of the
combinatorial auction will be higher than that of the
simultaneous auction. We also provide concrete examples
where the combinatorial auction is revenue-superior.}
}
@TechReport{ it:2008-026,
author = {Bj{\"o}rn Holmberg},
title = {Stereoscopic Estimation of Surface Movement from
Inter-Frame Matched Skin Texture},
institution = it,
department = syscon,
year = 2008,
number = {2008-026},
month = oct,
abstract = {Marker-less human motion analysis is currently a hot topic
in the research community. In this study three dimensional
motion of a human limb is estimated using a large number of
matched skin texture image patches. These two dimensional
matches are triangulated and also matched to the next time
frame. With these matched three dimensional points a Least
Squares estimate of the rigid body motion obtained using
standard methods. This motion estimate is subsequently
compared to a marker based estimate acquired from a
synchronized marker system.
The results show that this approach can be used for motion
estimation but with less accurate results than the marker
based system that is to be considered as the clinically
used standard. However, the correlation surfaces indicate
that the method has potential if for example subpixel
correlation algorithms were to be employed. }
}
@TechReport{ it:2008-025,
author = {Bj{\"o}rn Holmberg},
title = {High Dimensional Human Motion Estimation using Particle
Filtering},
institution = it,
department = syscon,
year = 2008,
number = {2008-025},
month = oct,
abstract = {An anatomical model of a human thigh and shank segment is
built. This 19 degree of freedom model is used in a
particle filtering implementation to estimate the model
state based on simulated data.
The novelty of this paper is in the use of the particle
filter with such a high dimensional model as well as the
application on a new type of data. This new data type is
inter-frame matched 3D points on the skin surface, based on
triangulation.
The results are very encouraging in comparison to state of
the art contributions. The present implementation is very
demanding in terms of computations and hence do not lend
itself to real time applications.}
}
@TechReport{ it:2008-024,
author = {Therese Bohlin and Bengt Jonsson},
title = {Regular Inference for Communication Protocol Entities},
institution = it,
department = docs,
year = 2008,
number = {2008-024},
month = sep,
abstract = {Existing algorithms for regular inference (aka automata
learning) allows to infer a finite state machine model of a
system under test (SUT) by observing the output that the
SUT produces in response to selected sequences of input. In
this paper we present an approach using regular inference
to construct models of communication protocol entities.
Entities of communication protocols typically take input
messages in the format of a protocol data unit (PDU) type
together with a number of parameters and produce output of
the same format. We assume that parameters from input can
be stored in state variables of communication protocols for
later use. A model of a communication protocol is usually
structured into control states. Our goal is to infer
symbolic extended finite state machine models of
communication protocol entities with control states in the
model that are similar to the control states in the
communication protocol. In our approach, we first apply an
existing regular inference algorithm to a communication
protocol entity to generate a finite state machine model of
the entity. Thereafter we fold the generated model into a
symbolic extended finite state machine model with locations
and state variables. We have applied parts of our approach
to an executable specification of the Mobile Arts Advanced
Mobile Location Center (A-MLC) protocol and evaluated the
results.}
}
@TechReport{ it:2008-023,
author = {Pierre Flener and Justin Pearson and Meinolf Sellmann},
title = {Static and Dynamic Structural Symmetry Breaking},
institution = it,
department = csd,
year = 2008,
number = {2008-023},
month = sep,
abstract = {We reconsider the idea of structural symmetry breaking for
constraint satisfaction problems (CSPs). We show that the
dynamic dominance checks used in symmetry breaking by
dominance-detection search for CSPs with piecewise variable
and value symmetries have a static counterpart: there
exists a set of constraints that can be posted at the root
node and that breaks all the compositions of these
(unconditional) symmetries. The amount of these
symmetry-breaking constraints is linear in the size of the
problem, and yet they are able to remove a
super-exponential number of symmetries on both values and
variables. Moreover, we compare the search trees under
static and dynamic structural symmetry breaking when using
fixed variable and value orderings. These results are then
generalised to wreath-symmetric CSPs with both variable and
value symmetries. We show that there also exists a
polynomial-time dominance-detection algorithm for this
class of CSPs, as well as a linear-sized set of constraints
that breaks these symmetries statically.}
}
@TechReport{ it:2008-022,
author = {Josef Cullhed and Stefan Engblom and Andreas Hellander},
title = {The {URDME} Manual version 1.0},
institution = it,
department = tdb,
year = 2008,
number = {2008-022},
month = sep,
abstract = {We have developed URDME, a general software for simulation
of stochastic reaction-diffusion processes on unstructured
meshes. This allows for a more flexible handling of
complicated geometries and curved boundaries compared to
simulations on structured, cartesian meshes. The underlying
algorithm is the next subvolume method (NSM), extended to
unstructured meshes by obtaining jump coefficients from the
finite element formulation of the corresponding macroscopic
equation.
In this manual, we describe how to use the software
together with COMSOL Multiphysics 3.4 and Matlab to set up
simulations. We provide a detailed account of the code
structure and of the available interfaces. This makes
modifications and extensions of the code possible. We also
give two detailed examples, in which we describe the
process of simulating and visualizing two models from the
systems biology literature in a step-by-step manner.}
}
@TechReport{ it:2008-021,
author = {{\AA}sa Cajander and Elina Eriksson and Jan Gulliksen and
Iordanis Kavathatzopoulos and Bengt Sandblad},
title = {Anv{\"a}ndbara IT-st{\"o}d - En utv{\"a}rdering av ett
forskningsprojekt vid CSN, Centrala studiest{\"o}dsn{\"a}mnden},
institution = it,
department = hci,
year = 2008,
number = {2008-021},
month = aug,
note = {In Swedish},
abstract = {Utvecklingsr{\aa}det f{\"o}r den statliga sektorn har
tagit ett initiativ f{\"o}r att st{\"o}dja myndigheternas
arbete med att f{\"o}rb{\"a}ttra arbetsmilj{\"o}n och
s{\"a}nka sjukfr{\aa}nvaron. D{\"a}rf{\"o}r startades
programmet Satsa friskt. Programmet ger st{\"o}d i form av
ekonomiskt bidrag och experthj{\"a}lp till olika projekt
inom statliga myndigheter. Ett av Satsa Friskts
insatsomr{\aa}den {\"a}r ~M{\"a}nniska ~ IT~. Inom detta
omr{\aa}de har det sedan 2004 bedrivits ett antal olika
projekt vid flera statliga verk. Vi har fr{\aa}n MDI
(avdelningen f{\"o}r m{\"a}nniska-datorinteraktion,
institutionen f{\"o}r informationsteknologi) vid Uppsala
universitet varit mer omfattande inblandad i tre olika
s{\aa}dana projekt: vid CSN, Migrationsverket och SMHI.
Syftet och inneh{\aa}llet har varierat en del mellan de
olika projekten, men ett huvudsakligt fokus har varit hur
man kan se till att de framtida IT-st{\"o}dda arbetena inom
myndigheterna blir effektivare och arbetsmilj{\"o}n
b{\"a}ttre. Genom att b{\"a}ttre beakta anv{\"a}ndbarhets-
och arbetsmilj{\"o}aspekter vid kravst{\"a}llande,
utveckling och inf{\"o}rande av IT-st{\"o}d kan man
st{\"o}dja en positiv utveckling av verksamheten som
s{\aa}dan liksom av arbetsinneh{\aa}ll och arbetsmilj{\"o}
f{\"o}r den enskilde individen. Resultatet kan d{\aa} bli
effektivare verksamhet, b{\"a}ttre service till kunder och
ett h{\"a}lsosammare och h{\aa}llbarare arbete f{\"o}r de
anst{\"a}llda. Denna rapport beskriver det arbete som under
{\aa}ren 2005-2007 genomf{\"o}rts i samverkan mellan CSN,
Centrala studiest{\"o}dsn{\"a}mnden, och MDI, Uppsala
universitet. F{\"o}rutom en kort beskrivning av
inneh{\aa}llet i det arbete som gjorts inom projektet
redovisar denna rapport en utv{\"a}rdering av resultatet,
de l{\"a}rdomar som vi gjort fr{\aa}n projektet, de r{\aa}d
vi kan ge till andra som vill ta del av dessa l{\"a}rdomar
samt en f{\"o}rteckning av de rapporter av olika slag som producerats.}
}
@TechReport{ it:2008-020,
author = {Stefan Engblom},
title = {Parallel in Time Simulation of Multiscale Stochastic
Chemical Kinetics},
institution = it,
department = tdb,
year = 2008,
number = {2008-020},
month = aug,
note = {Extended abstract to appear in Proceedings of ICNAAM
2008},
abstract = {A version of the time-parallel algorithm parareal is
analyzed and applied to stochastic models in chemical
kinetics. A fast predictor at the macroscopic scale
(evaluated in serial) is available in the form of the usual
reaction rate equations. A stochastic simulation algorithm
is used to obtain an exact realization of the process at
the mesoscopic scale (in parallel).
The underlying stochastic description is a jump process
driven by the Poisson measure. A convergence result in this
arguably difficult setting is established suggesting that a
homogenization of the solution is advantageous. We devise a
simple but highly general such technique.
Three numerical experiments on models representative to the
field of computational systems biology illustrate the
method. For non-stiff problems, it is shown that the method
is able to quickly converge even when stochastic effects
are present. For stiff problems we are instead able to
obtain fast convergence to a homogenized solution.
Overall, the method builds an attractive bridge between on
the one hand, macroscopic deterministic scales and, on the
other hand, mesoscopic stochastic ones. This construction
is clearly possible to apply also to stochastic models
within other fields. }
}
@TechReport{ it:2008-019,
author = {Ken Mattsson and Frank Ham and Gianluca Iaccarino},
title = {Stable Boundary Treatment for the Wave Equation on
Second-Order Form},
institution = it,
department = tdb,
year = 2008,
number = {2008-019},
month = jun,
abstract = {A stable and accurate boundary treatment is derived for
the second-order wave equation. The domain is discretized
using narrow-diagonal summation by parts operators and the
boundary conditions are imposed using a penalty method,
leading to fully explicit time integration. This
discretization yields a stable and efficient scheme. The
analysis is verified by numerical simulations in
one-dimension using high-order finite difference
discretizations, and in three-dimensions using an
unstructured finite volume discretization.}
}
@TechReport{ it:2008-018,
author = {Pierre Flener and Xavier Lorca},
title = {A Complete Characterisation of the Classification Tree
Problem},
institution = it,
department = csd,
year = 2008,
number = {2008-018},
month = jun,
abstract = {Finding a classification tree over a given set of elements
that is compatible with a given family of classification
trees over subsets of that set is a common problem in many
application areas, such as the historical analysis of
languages, the theory of relational databases, and
phylogenetic supertree construction. We present a
constraint programming approach to this problem. First, we
introduce a natural and compact graph representation of a
family of classification trees. Second, we provide a
complete filtering algorithm for the classification tree
problem, based on this normal form.}
}
@TechReport{ it:2008-017,
author = {Henrik Johansson},
title = {Design and Implementation of a Dynamic and Adaptive
Meta-Partitioner for Parallel {SAMR} Grid Hierarchies},
institution = it,
department = tdb,
year = 2008,
number = {2008-017},
month = jun,
abstract = {In this paper we present a pilot implementation of the
Meta-Partitioner, a partitioning framework that
automatically selects, configures, and invokes suitable
partitioning algorithms for Structured Adaptive Mesh
Refinement (SAMR) applications. Efficient use of SAMR on
parallel computers requires that the dynamic grid hierarchy
is repeatedly repartitioned and redistributed. The
partitioning process needs to consider all factors that
contribute to the run-time, i.e. computational load,
communication volume, synchronization delays, and data
movement. There is no partitioning algorithm that performs
well for all possible grid hierarchies --- instead the
algorithms must be selected dynamically during run-time.
At each repartitioning, the Meta-Partitioner uses
performance data from previously encountered application
states to select the partitioning algorithm with the best
predicted performance. Before the repartition, we determine
a partitioning focus to direct the partitioning effort to
the performance-inhibiting factor that currently has the
largest impact on the execution time.
The implementation uses component-based software
engineering (CBSE) to allow for easy expansion and
modification. Also, by employing CBSE it is easy to adapt
existing SAMR engines for use with the Meta-Partitioner.}
}
@TechReport{ it:2008-016,
author = {Parosh Aziz Abdulla and Pavel Krcal and Wang Yi},
title = {R-automata},
institution = it,
department = docs,
year = 2008,
number = {2008-016},
month = jun,
abstract = {We introduce \emph{R-automata} -- a model for analysis of
systems with resources which are consumed in small parts
but which can be replenished at once. An R-automaton is a
finite state machine which operates on a finite number of
unbounded counters (modeling the resources). The values of
the counters can be incremented, reset to zero, or left
unchanged along the transitions. We define the language
accepted by an R-automaton relative to a natural number $D$
as the set of words allowing a run along which no counter
value exceeds $D$. As the main result, we show decidability
of the universality problem, i.e., the problem whether
there is a number $D$ such that the corresponding language
is universal. The decidability proof is based on a
reformulation of the problem in the language of finite
monoids and solving it using the factorization forest
theorem. This approach extends the way in which the
factorization forest theorem was used to solve the
limitedness problem for distance automata in Simon, 1994.
We also show decidability of the non-emptiness problem and
the limitedness problem, i.e., whether there is a natural
number $D$ such that the corresponding language is
non-empty resp.\ all the accepted words can also be
accepted with counter values smaller than $D$. Finally, we
extend the decidability results to R-automata with B\"uchi
acceptance conditions.}
}
@TechReport{ it:2008-015,
author = {Parosh Aziz Abdulla and Ahmed Bouajjani and Jonathan
Cederberg and Fr{\'e}d{\'e}ric Haziza and Ahmed Rezine},
title = {Monotonic Abstraction for Programs with Dynamic Memory
Heaps},
institution = it,
department = docs,
year = 2008,
number = {2008-015},
optmonth = {},
abstract = {We propose a new approach for automatic verification of
programs with dynamic heap manipulation. The method is
based on symbolic (backward) reachability analysis using
upward-closed sets of heaps w.r.t. an appropriate preorder
on graphs. These sets are represented by a finite set of
minimal graph patterns corresponding to a set of bad
configurations. We define an abstract semantics for the
programs which is monotonic w.r.t. the preorder. Moreover,
we prove that our analysis always terminates by showing
that the preorder is a well-quasi ordering. Our results are
presented for the case of programs with 1-next selector. We
provide experimental results showing the effectiveness of
our approach. }
}
@TechReport{ it:2008-014,
author = {Olga Grinchtein and Bengt Jonsson},
title = {Inference of Event-Recording Automata using Timed Decision
Trees},
institution = it,
department = docs,
year = 2008,
number = {2008-014},
month = apr,
abstract = {In \emph{regular inference}, the problem is to infer a
regular language, typically represented by a deterministic
finite automaton (DFA) from answers to a finite set of
membership queries, each of which asks whether the language
contains a certain word. There are many algorithms for
learning DFAs, the most well-known being the $L^*$
algorithm due to Dana Angluin. However, there are almost no
extensions of these algorithms to the setting of timed
systems. We present an algorithm for inferring a model of a
timed system using Angluin's setup. One of the most popular
model for timed system is timed automata. Since timed
automata can freely use an arbitrary number of clocks, we
restrict our attention to systems that can be described by
\emph{event-recording automata} (DERAs). In previous work,
we have presented an algorithm for inferring a DERA in the
form of a region graph. In this paper, we present a novel
inference algorithm for DERAs, which avoids constructing a
(usually prohibitively large) region graph. We must then
develop techniques for inferring guards on transitions of a
DERA. Our construction deviates from previous work on
inference of DERAs in that it first constructs a so called
timed decision tree from observations of system behavior,
which is thereafter folded into an automaton.}
}
@TechReport{ it:2008-013,
author = {Olga Grinchtein and Bengt Jonsson and Martin Leucker},
title = {Learning of Event-Recording Automata},
institution = it,
department = docs,
year = 2008,
number = {2008-013},
month = apr,
abstract = {In regular inference, a regular language is inferred from
answers to a finite set of membership queries, each of
which asks whether the language contains a certain word.
One of the most well-known regular inference algorithms is
the $L^*$ algorithm due to Dana Angluin. However, there are
almost no extensions of these algorithms to the setting of
timed systems. We extend Angluin's algorithm for on-line
learning of regular languages to the setting of timed
systems. Since timed automata can freely use an arbitrary
number of clocks, we restrict our attention to systems that
can be described by deterministic event-recording automata
(DERAs). We present three algorithms, $TL_sg^*$, $TL_nsg^*$
and $TL_s^*$, for inference of DERAs. In $TL_sg^*$ and
$TL_nsg^*$, we further restrict event-recording automata to
be event-deterministic in the sense that each state has at
most one outgoing transition per action; learning such an
automaton becomes significantly more tractable. The
algorithm $TL_nsg^*$ builds on $TL_sg^*$, by attempts to
construct a smaller (in number of locations) automaton.
Finally, $TL_s^*$ is a learning algorithm for a full class
of deterministic event-recording automata, which infers a
so called \emph{simple} DERA, which is similar in spirit to
the region graph.}
}
@TechReport{ it:2008-012,
author = {Stefan Engblom and Lars Ferm and Andreas Hellander and Per
L{\"o}tstedt},
title = {Simulation of Stochastic Reaction-Diffusion Processes on
Unstructured Meshes},
institution = it,
department = tdb,
year = 2008,
number = {2008-012},
month = apr,
abstract = {Stochastic chemical systems with diffusion are modeled
with a reaction-diffusion master equation. On a macroscopic
level, the governing equation is a reaction-diffusion
equation for the averages of the chemical species. On a
mesoscopic level, the master equation for a well stirred
chemical system is combined with Brownian motion in space
to obtain the reaction-diffusion master equation. The space
is covered by an unstructured mesh and the diffusion
coefficients on the mesoscale are obtained from a finite
element discretization of the Laplace operator on the
macroscale. The resulting method is a flexible hybrid
algorithm in that the diffusion can be handled either on
the meso- or on the macroscale level. The accuracy and the
efficiency of the method are illustrated in three numerical
examples inspired by molecular biology.}
}
@TechReport{ it:2008-011,
author = {Per Pettersson and Gianluca Iaccarino and Jan
Nordstr{\"o}m},
title = {Numerical Analysis of {B}urgers' Equation with Uncertain
Boundary Conditions Using the Stochastic {G}alerkin
Method},
institution = it,
department = tdb,
year = 2008,
number = {2008-011},
month = mar,
abstract = {Burgers' equation with stochastic initial and boundary
conditions is investigated by a polynomial chaos expansion
approach where the solution is represented as a series of
stochastic, orthogonal polynomials. The analysis of
wellposedness for the stochastic Burgers' equation follows
the pattern of that of the deterministic Burgers' equation.
We use dissipation and spatial derivative operators
satisfying the summation by parts property and weak
boundary conditions to ensure stability. Similar to the
deterministic case, the time step for hyperbolic stochastic
problems solved with explicit methods is proportional to
the inverse of the largest eigenvalue of the system matrix.
The time step naturally decreases compared to the
deterministic case since the spectral radius of the
continuous problem grows with the number of polynomial
chaos coefficients.
Analysis of the characteristics of a truncated system gives
a qualitative description of the development of the system
over time for different initial and boundary conditions.
Knowledge of the initial and boundary expected value and
variance is not enough to get a unique solution. Also, the
sign of the polynomial chaos coefficients must be known.
The deterministic component (expected value) of the
solution is affected by the modeling of uncertainty. A
shock discontinuity in a purely deterministic problem can
be made smooth by assuming uncertain boundary conditions.}
}
@TechReport{ it:2008-010,
author = {Parosh Aziz Abdulla and Noomene Ben Henda and Giorgio
Delzanno and Fr{\'e}d{\'e}ric Haziza and Ahmed Rezine},
title = {Parameterized Tree Systems},
institution = it,
department = docs,
year = 2008,
number = {2008-010},
month = mar,
note = {Accepted at FORTE'08:
\url{http://www-higashi.ist.osaka-u.ac.jp/FORTE08/}.},
abstract = {Several recent works have considered \emph{parameterized
verification}, i.e.\ automatic verification of systems
consisting of an arbitrary number of finite-state processes
organized in a \emph{linear array}. The aim of this paper
is to extend these works by giving a simple and efficient
method to prove safety properties for systems with
\emph{tree-like} architectures. A process in the system is
a finite-state automaton and a transition is performed
jointly by a process and its parent and children processes.
The method derives an over-approximation of the induced
transition system, which allows the use of finite trees as
symbolic representations of infinite sets of
configurations. Compared to traditional methods for
parameterized verification of systems with tree topologies,
our method does not require the manipulation of tree
transducers, hence its simplicity and efficiency. We have
implemented a prototype which works well on several
nontrivial tree-based protocols.}
}
@TechReport{ it:2008-009,
author = {Peter Naucl{\'e}r and Torsten S{\"o}derstr{\"o}m},
title = {Linear and Nonlinear Regression with Application to
Unbalance Estimation},
institution = it,
department = syscon,
year = 2008,
number = {2008-009},
month = mar,
abstract = {This paper considers estimation of parameters that enters
nonlinearly in a regression model. The problem formulation
is closely connected to unbal- ance estimation of rotating
machinery. The parameter estimation problem can after
approximation be formulated as a linear estimation
procedure, while neglecting the effects of the disturbing
term. Two such estimators are derived. In addition, a third
approach that handles the uncertainty in a statistically
sound way is presented. The three methods are compared and
analyzed with respect to their statistical accuracy. Using
the example of unbalance estimation of a separator, the
nonlinear approach is shown to outperform the other two.}
}
@TechReport{ it:2008-008,
author = {Mei Hong and Torsten S{\"o}derstr{\"o}m},
title = {Relations between Bias-Eliminating Least Squares, the
{F}risch Scheme and Extended Compensated Least Squares
Methods for Identifying Errors-in-Variables Systems},
institution = it,
department = syscon,
year = 2008,
number = {2008-008},
month = mar,
abstract = {There are many methods for identifying errors-in-variables
systems. Among them Bias-Eliminating Least Squares (BELS),
the Frisch scheme and Extended Compensated Least Squares
(ECLS) methods are attractive approaches because of their
simplicity and good estimation accuracy. These three
methods are all based on a bias-compensated least-squares
(BCLS) principle. In this report, the relations between
them are considered. In particular, the nonlinear equations
utilized in these three methods are proved to be equivalent
under different noise conditions. It is shown that BELS,
Frisch and ECLS methods have the same asymptotic estimation
accuracy providing the same extended vector is used.}
}
@TechReport{ it:2008-007,
author = {Torbj{\"o}rn Wigren and Linda Brus},
title = {{MATLAB} Software for Recursive Identification and Scaling
Using a Structured Nonlinear Black-box Model - Revision 4},
institution = it,
department = syscon,
year = 2008,
number = {2008-007},
month = mar,
note = {Revised version of nr 2007-013. The software package can
be downloaded from
\url{http://www.it.uu.se/research/publications/reports/2008-007/NRISoftwareRev4.zip}.
\textbf{Note} that the software package was updated on
2010-03-16.},
abstract = {This reports is intended as a users manual for a package
of MATLAB scripts and functions, developed for recursive
prediction error identification of nonlinear state space
systems and nonlinear static systems. The core of the
package is an implementation of an output error
identification and scaling algorithm. The algorithm is
based on a continuous time, structured black box state
space model of a nonlinear system. An RPEM algorithm for
recursive identification of nonlinear static systems, that
re-uses the parameterization of the nonlinear ODE model, is
also included in the software package. In this version of
the software an initialization algorithm based on Kalman
filter theory has been added to the package. The purpose of
the initialization algorithm is to find initial parameters
for the prediction error algorithm, and thus reduce the
risk of convergence to local minima for the nonlinear
identification problem. The software can only be run
off-line, i.e. no true real time operation is possible. The
algorithms are however implemented so that true on-line
operation can be obtained by extraction of the main
algorithmic loop. The user must then provide the real time
environment. The software package contains scripts and
functions that allow the user to either input live
measurements or to generate test data by simulation. The
scripts and functions for the setup and execution of the
identification algorithms are somewhat more general than
what is described in the references. There is e.g. support
for automatic re-initiation of the algorithms using the
parameters obtained at the end of a previous identification
run. This allows for multiple runs through a set of data,
something that is useful for data sets that are too short
to allow convergence in a single run. The re-initiation
step also allows the user to modify the degrees of the
polynomial model structure and to specify terms that are to
be excluded from the model. This makes it possible to
iteratively re-fine the estimated model using multiple
runs. The functionality for display of results include
scripts for plotting of data, parameters, prediction
errors, eigenvalues and the condition number of the
Hessian. The estimated model obtained at the end of a run
can be simulated and the model output plotted, alone or
together with the data used for identification. Model
validation is supported by two methods apart from the
display functionality. First, a calculation of the RPEM
loss function can be performed, using parameters obtained
at the end of an identification run. Secondly, the accuracy
as a function of the output signal amplitude can be
assessed.}
}
@TechReport{ it:2008-006,
author = {Linda Brus},
title = {{MATLAB} Software for Feedforward Optimal Control of
Systems with Flow Varying Time Delays - Revision 2},
institution = it,
department = syscon,
year = 2008,
number = {2008-006},
month = mar,
note = {The software package can be downloaded from
\url{http://www.it.uu.se/research/publications/reports/2008-006/NOCSoftwareV2.zip}}
,
abstract = {This report describes a software package for optimal
control of a nonlinear system with flow variant time delay.
The software was developed for control of a solar plant in
Seville, Spain, and is tailored to this application. The
optimization is performed using an algorithm with gradient
based minimum search. }
}
@TechReport{ it:2008-005,
author = {Stefan Engblom},
title = {A Discrete Spectral Method for the Chemical Master
Equation},
institution = it,
department = tdb,
year = 2008,
number = {2008-005},
month = feb,
note = {Supersedes report nr 2006-036. Updated Feb 29, 2008.},
abstract = {As an equivalent formulation of the Markov-assumption of
stochastic processes, the master equation of chemical
reactions is an accurate description of general systems in
chemistry. For $D$ reacting species this is a
differential-difference equation in $D$ dimensions, exactly
soluble for very simple systems only.
We present and analyze a novel solution strategy based upon
a Galerkin spectral method with an inherent natural
adaptivity and a very favorable choice of basis functions.
The method is demonstrated by the numerical solution of two
model problems followed by two more realistic systems taken
from molecular biology. It is shown that the method remains
effective and accurate, providing a viable alternative to
other solution methods when the dimensionality is not too
high.}
}
@TechReport{ it:2008-004,
author = {Arne Andersson and Jim Wilenius},
title = {A New Analysis of Combinatorial vs Simultaneous Auctions:
Revenue and Efficiency},
institution = it,
department = csd,
year = 2008,
number = {2008-004},
month = feb,
abstract = {We address the fundamental issue of revenue and efficiency
in the combinatorial and simultaneous auction using a novel
approach. Specifically, upper and lower bounds are
constructed for the first-price sealed-bid setting of these
two auctions.
The question of revenue is important yet very few results
can be found in the literature. Only for very small
instances with 2 items have comparisons been made. Krishna
et. al. find that allowing combinatorial bids result in
lower revenue compared to a second price simultaneous
auction.
We formulate a lower bound on the first-price combinatorial
auction and an upper bound on the first-price simultaneous
auction for larger problems with several items and many
bidders, in a model where bidders have synergies from
winning a specific set of items. We show that the
combinatorial auction is revenue superior to the
simultaneous auction for a specific instance in pure
symmetric equilibrium and give two generalized upper bounds
on revenue for the simultaneous auction.}
}
@TechReport{ it:2008-003,
author = {Iordanis Kavathatzopoulos},
title = {Ett f{\"o}rb{\"a}ttrat verktyg f{\"o}r m{\"a}tning av
anv{\"a}ndbarhet, stress och nytta: Andra f{\"o}rs{\"o}ket
inom {CSN}},
institution = it,
department = hci,
year = 2008,
number = {2008-003},
month = jan,
note = {In Swedish.},
abstract = {Syftet med detta arbete {\"a}r att utveckla ett index
f{\"o}r att beskriva anv{\"a}ndbarheten hos ITverktyg och
hur anv{\"a}ndbarheten p{\aa}verkar effektiviteten.
Enk{\"a}ten pr{\"o}vades inom CSN f{\"o}rst p{\aa}
STIS2000. Resultaten ledde till en f{\"o}rb{\"a}ttrad
version av enk{\"a}ten som pr{\"o}vades h{\"o}sten 2006
p{\aa} E-posthandl{\"a}ggningen. 427 personer deltog i
unders{\"o}kningen. Sammanh{\aa}llningen av enk{\"a}tens
delar och fr{\aa}gor samt tillf{\"o}rlitligheten har blivit
b{\"a}ttre vilket g{\"o}r det l{\"a}ttare att utveckla ett
anv{\"a}ndbarhetsindex. Svaren visar ocks{\aa} att
deltagarna {\"a}r i stort neutrala n{\"a}r det g{\"a}ller
anv{\"a}ndbarheten av E-posthandl{\"a}ggningen inom CSN.}
}
@TechReport{ it:2008-002,
author = {Owe Axelsson and Janos Karatson},
title = {Equivalent Operator Preconditioning for Linear Elliptic
Problems},
institution = it,
department = tdb,
year = 2008,
number = {2008-002},
month = jan,
note = {A preliminary version of the same article is published as
Preprint 2007-04, ELTE Dept. Appl. Anal. Comp. Math.,
\url{http://www.cs.elte.hu/applanal/preprints}},
abstract = {The numerical solution of linear elliptic partial
differential equations most often involves a finite element
or finite difference discretization. To preserve sparsity,
the arising system is normally solved using an iterative
solution method, commonly a preconditioned conjugate
gradient method. Preconditioning is a crucial part of such
a solution process. It is desirable that the total
computational cost will be optimal, i.e. proportional to
the degrees of freedom of the approximation used, which
also includes mesh independent convergence of the
iteration. This paper surveys the equivalent operator
approach, which has proven to provide an efficient general
framework to construct such preconditioners. Hereby one
first approximates the given differential operator by some
simpler differential operator, and then one chooses as
preconditioner the discretization of this operator for the
same mesh. In this survey we give a uniform presentation of
this approach, including theoretical foundation and several
practically important applications.}
}
@TechReport{ it:2008-001,
author = {Bj{\"o}rn Holmberg and Bo Nordin and Ewert Bengtsson and
H{\aa}kan Lanshammar},
title = {On the Plausibility of Using Skin Texture as Virtual
Markers in the Human Motion Analysis Context, a {2D}
Study},
institution = it,
department = syscon,
year = 2008,
number = {2008-001},
month = jan,
abstract = {For the first time it is shown that skin texture can be
used as a means to match human limb surfaces between
different image frames. The results are limited to motion
in two dimensions. It is shown that images with a
resolution that can be produced in today existing video
camera hardware are usable. This is very encouraging for
the future of clinical marker free human motion analysis
applications. The next step will be to investigate if these
results can be extended to three dimensions using a stereo
camera setup.
The method uses histogram information as a means to match
small image patches to one another. The histogram matching
is performed using a Mutual Information criterion as the
cost function and Simulated Annealing as the optimization
algorithm. }
}
@TechReport{ it:2007-035,
author = {Mayank Saksena and Oskar Wibling and Bengt Jonsson},
title = {Graph Grammar Modeling and Verification of Ad Hoc Routing
Protocols},
institution = it,
department = docs,
year = 2007,
number = {2007-035},
month = dec,
note = {Updated March 2008. Extended abstract to appear in proc.
14th Int. Conf. on Tools and Algorithms for the
Construction and Analysis of Systems (TACAS 2008).},
abstract = {We present a technique for modeling and automatic
verification of network protocols, based on graph
transformation. It is suitable for protocols with a
potentially unbounded number of nodes, in which the
structure and topology of the network is a central aspect,
such as routing protocols for ad hoc networks. Safety
properties are specified as a set of undesirable global
configurations. We verify that there is no undesirable
configuration which is reachable from an initial
configuration, by means of symbolic backward reachability
analysis. In general, the reachability problem is
undecidable. We implement the technique in a graph grammar
analysis tool, and automatically verify several interesting
non-trivial examples. Notably, we prove loop freedom for
the DYMO ad hoc routing protocol. DYMO is currently on the
IETF standards track, to potentially become an Internet
standard.}
}
@TechReport{ it:2007-034,
author = {Stefan Seipel and Lars Winkler Pettersson},
title = {{P}ixel{A}ctive{S}urface: A Tabletop Rear-Projection
Display for Collaboration with Pixel-Accurate Interaction},
institution = it,
department = hci,
year = 2007,
number = {2007-034},
month = dec,
note = {Extended abstract appeared in ACM Conference on Supporting
Group Work (GROUP'07).},
abstract = {The use of table-top displays as working environment
provides a very natural way to present and interact with
information. In particular when several users intend an
unhindered face-to-face dialogue, horizontal displays have
been introduced as efficient tools for collaborative work
in shared physical spaces. Many of the hardware systems
presented so far are composed of several independent and
technically often clumsy components for the display and for
tracking of users' head positions or gestures,
respectively. This hampers, in practice, easy operation and
a more widespread use of table-top displays in real working
environments. In this paper, we present our technical
solution for a fully integrated, small sized table-top
visualization environment that provides head position
tracking for two collaborating users, stereoscopic
projection and high resolution multi-point screen
interaction. Our solution is intended as a self-contained
out-of-the-box system that is affordable and easy to use.
The real novelty with our technique presented in this paper
is, however, that we succeeded in combining high resolution
and multi-point pen-based interaction technology based on
optical pattern recognition with a rear-projection screen,
which opens up for a wider field of applications not only
limited to tabletop display environments.}
}
@TechReport{ it:2007-033,
author = {Owe Axelsson and Radim Blaheta and Maya Neytcheva},
title = {A Black-Box Generalized Conjugate Gradient Minimum
Residual Method Based on Variable Preconditioners and Local
Element Approximations},
institution = it,
department = tdb,
year = 2007,
number = {2007-033},
month = dec,
abstract = {In order to control the accuracy of a preconditioner for
an outer iterative process one often involves variable
preconditioners. The variability may for instance be due to
the use of inner iterations in the construction of the
preconditioner. Both the outer and inner iterations may be
based on some conjugate gradient type of method, e.g.
generalized minimum residual methods.
A background for such methods, including results about
their computational complexity and rate of convergence, is
given. It is then applied for a variable preconditioner
arising for matrices partitioned in two-by-two block form.
The matrices can be unsymmetric and also indefinite. The
aim is to provide a black--box solver, applicable for all
ranges of problem parameters such as coefficient jumps and
anisotropy.
When applying this approach for elliptic boundary value
problems, in order to achieve the latter aim, it turns out
to be efficient to use local element approximations of
arising block matrices as preconditioners for the inner
iterations.
It is illustrated by numerical examples how the convergence
rate of the inner-outer iteration method approaches that
for the more expensive fixed preconditioner when the
accuracies of the inner iterations increase.}
}
@TechReport{ it:2007-032,
author = {Pierre Flener and Justin Pearson and Meinolf Sellmann and
Van Hentenryck, Pascal and Magnus {\AA}gren},
title = {Structural Symmetry Breaking for Constraint Satisfaction
Problems},
institution = it,
department = csd,
year = 2007,
number = {2007-032},
month = nov,
abstract = {In recent years, symmetry breaking for constraint
satisfaction problems (CSPs) has attracted considerable
attention. Various general schemes have been proposed to
eliminate symmetries. In general, these schemes may take
exponential space or time to eliminate all the symmetries.
We identify several classes of CSPs that encompass many
practical problems and for which symmetry breaking for
various forms of value or variable interchangeability is
tractable using dedicated search procedures. We also show
the limits of efficient symmetry breaking for such
dominance-detection schemes by proving intractability
results for some classes of CSPs. }
}
@TechReport{ it:2007-031,
author = {Niklas Hardenborg and Iordanis Kavathatzopoulos and Bengt
Sandblad},
title = {Performing the Vision Seminar Process},
institution = it,
department = hci,
year = 2007,
number = {2007-031},
month = nov,
abstract = {The Vision Seminar Process is a process for developing an
efficient, sustainable, IT-supported future work and a tool
for proving a solid basis for the development of IT
systems. The process provides a framework where
practitioners and designers cooperate in the design of both
sustainable work and usable IT systems. A practical
approach is provided to facilitate for practitioners'
reflective in-depth analysis of their work practices as
well as to question and discuss their entire work situation
and organization.
This report gives a practical and basic description of the
process procedure based on experiences from several
projects where the process has been carried out in
different contexts and organizations.}
}
@TechReport{ it:2007-030,
author = {Parosh Abdulla and Noomene Ben Henda and Giorgio Delzanno
and Ahmed Rezine},
title = {Handling Parameterized Systems with Non-Atomic Global
Conditions},
institution = it,
department = docs,
year = 2007,
number = {2007-030},
month = nov,
note = {Updated 20 Mar 2008. To appear in the Proc. of VMCAI
2008},
abstract = {We consider verification of safety properties for
parameterized systems with linear topologies. A process in
the system is an extended automaton, where the transitions
are guarded by both local and global conditions. The global
conditions are non-atomic, i.e., a process allows arbitrary
interleavings with other transitions while checking the
states of all (or some) of the other processes. We
translate the problem into model checking of infinite
transition systems where each configuration is a labeled
finite graph. We derive an over-approximation of the
induced transition system, which leads to a symbolic scheme
for analyzing safety properties. We have implemented a
prototype and run it on several nontrivial case studies,
namely non-atomic versions of Burn's protocol, Dijkstra's
protocol, the Bakery algorithm, Lamport's distributed
mutual exclusion protocol, and a two-phase commit protocol
used for handling transactions in distributed systems. As
far as we know, these protocols have not previously been
verified in a fully automated framework.}
}
@TechReport{ it:2007-029,
author = {Jing Gong and Jan Nordstr{\"o}m and van der Weide, Edwin},
title = {A Hybrid Method for the Unsteady Compressible
{N}avier-{S}tokes Equations},
institution = it,
department = tdb,
year = 2007,
number = {2007-029},
month = oct,
abstract = {A hybrid method composed of finite difference-finite
difference and finite difference-finite volume schemes for
the time-dependent Navier-Stokes equations has been
developed. A detailed analysis of the stability of the
proposed algorithms, paying special attention to the
stability of the interfaces between the subdomains is
performed. We prove that the interface coupling is stable
and conservative. This techniques makes it possible to
combine the efficiency of the finite difference method and
the flexibility of the finite volume schemes. We exemplify
the procedure by using finite difference methods. The
computational results corroborate the theoretical
analysis.}
}
@TechReport{ it:2007-028,
author = {Paul Sj{\"o}berg},
title = {{PDE} and {M}onte {C}arlo Approaches to Solving the Master
Equation Applied to Gene Regulation},
institution = it,
department = tdb,
year = 2007,
number = {2007-028},
month = oct,
abstract = {The \textit{Fokker-Planck equation} (FPE) approximation is
applied for a subspace of the state space of the
\textit{chemical master equation} (CME). The CME-FPE-hybrid
method exploits the lower cost of the FPE approximation
compared to the full CME. A fourth order finite difference
approximation of the FPE part of the hybrid is described
and demonstrated on a biologically relevant model in five
dimensions.}
}
@TechReport{ it:2007-027,
author = {Andreas Hellander},
title = {Efficient Computation of Transient Solutions of the
Chemical Master Equation Based on Uniformization and
Quasi-{M}onte {C}arlo},
institution = it,
department = tdb,
year = 2007,
number = {2007-027},
month = oct,
abstract = {A Quasi-Monte Carlo method for the simulation of discrete
time Markov chains is applied to the simulation of
biochemical reaction networks. The continuous process is
formulated as a discrete chain subordinate to a Poisson
process using the method of uniformization. It is shown
that a substantial reduction of the number of trajectories
that is required for an accurate estimation of the
probability density functions (PDF) can be achieved with
this technique. The method is applied to the simulation of
two model problems. Although the technique employed here
does not address the typical stiffness of such systems, it
is useful when computing the PDF by replication and the
method can be used in conjuncture with hybrid methods that
reduce the stiffness.}
}
@TechReport{ it:2007-026,
author = {Linda Brus},
title = {{MATLAB} Software for Feedforward Optimal Control of
Systems with Flow Varying Time Delays},
institution = it,
department = syscon,
year = 2007,
number = {2007-026},
month = sep,
note = {A revised version can be found as technical report nr
2008-006. The software package can be downloaded from
\url{http://www.it.uu.se/research/publications/reports/2007-026/NOCSoftware.zip}}
,
abstract = {This report describes a software package for optimal
control of a nonlinear system with flow variant time delay.
The software was developed for control of a solar plant in
Seville, Spain, and is tailored to this application. The
optimization is performed using an algorithm with gradient
based minimum search.}
}
@TechReport{ it:2007-025,
author = {Peter Naucl{\'e}r and Torsten S{\"o}derstr{\"o}m},
title = {Polynomial Feedforward Design Techniques for a Mechanical
Wave Diode System},
institution = it,
department = syscon,
year = 2007,
number = {2007-025},
month = sep,
abstract = {This paper considers feedforward control of extensional
waves in a bar. The system is designed to have properties
analogous to those of an electrical diode and is therefore
referred to as a mechanical wave diode. We present three
different feedforward control strategies. Two of them
relies on an `ideal' design which is derived in the
noise-free case, whereas the third is based on Wiener
filtering theory.
The control strategies are compared and evaluated for
different signal models and in the presence of measurement
noise. We show that the performance of the device is
improved by using the (optimal) Wiener feedforward filter.
}
}
@TechReport{ it:2007-024,
author = {John H{\aa}kansson and Paul Pettersson},
title = {Partial Order Reduction for Verification of Real-Time
Components},
institution = it,
department = docs,
year = 2007,
number = {2007-024},
month = sep,
note = {A shorter version will appear in the Proceedings of
FORMATS 2007, LNCS 4762, pp 211-226.},
abstract = {We describe a partial order reduction technique for a
real-time component model. Components are described as
timed automata with data ports, which can be composed in
static structures of unidirectional control and data flow.
Compositions can be encapsulated as components and used in
other compositions to form hierarchical models. The
proposed partial order reduction technique uses a local
time semantics for timed automata, in which time may
progress independently in parallel automata which are
resynchronized when needed. To increase the number of
independent transitions and to reduce the problem of
re-synchronizing parallel automata we propose, and show
how, to use information derived from the composition
structure of an analyzed model. Based on these ideas, we
present a reachability analysis algorithm that uses an
ample set construction to select which symbolic transitions
to explore. The algorithm has been implemented as a
prototype extension of the real-time model-checker UPPAAL.
We report from experiments with the tool that indicate that
the technique can achieve substantial reduction in the time
and memory needed to analyze a real-time system described
in the studied component model. }
}
@TechReport{ it:2007-023,
author = {Lars Ferm and Per L{\"o}tstedt},
title = {Adaptive Solution of the Master Equation in Low
Dimensions},
institution = it,
department = tdb,
year = 2007,
number = {2007-023},
month = sep,
abstract = {The master equation satisfied by a probability density
function is solved on a grid with a cell size $h>1.$ A
modified master equation is derived for the time
development of the average of the density in the larger
cells. The accuracy of the approximation is studied and the
total probability is conserved. Based on an estimate of the
discretization error, the cell size is dynamically adapted
to the solution. The method is suitable for a few space
dimensions and is tested on a model for the migration of
people. Substantial savings in memory requirements and CPU
times are reported in numerical experiments.}
}
@TechReport{ it:2007-022,
author = {Mei Hong and Torsten S{\"o}derstr{\"o}m and Johan
Schoukens and Rik Pintelon},
title = {Accuracy Analysis of Time Domain Maximum Likelihood Method
and Sample Maximum Likelihood Method for
Errors-in-Variables Identification},
institution = it,
department = syscon,
year = 2007,
number = {2007-022},
month = sep,
abstract = {The time domain maximum likelihood (TML) method and the
sample maximum Likelihood (SML) method are two approaches
for identifying errors-in-variables models. Both methods
may give the optimal estimation accuracy (achieve
Cram\'er-Rao lower bound) but in different senses. In the
TML method, an important assumption is that the noise-free
input signal is modeled as a stationary process with
rational spectrum. For SML, the noise-free input needs to
be periodic. It is interesting to know which of these
assumptions contain more information to boost the
estimation performance. In this paper, the estimation
accuracy of the two methods is analyzed statistically.
Numerical comparisons between the two estimates are also
done under different signal-to-noise ratios (SNRs). The
results suggest that TML and SML have similar estimation
accuracy at moderate or high SNR.}
}
@TechReport{ it:2007-021,
author = {Mei Hong and Torsten S{\"o}derstr{\"o}m and Umberto
Soverini and Roberto Diversi},
title = {Comparison of Three {F}risch Methods for
Errors-in-Variables Identification},
institution = it,
department = syscon,
year = 2007,
number = {2007-021},
month = aug,
abstract = {The errors--in--variables framework concerns static or
dynamic systems whose input and output variables are
affected by additive noise. Several estimation methods have
been proposed for identifying dynamic errors--in--variables
models. One of the more promising approaches is the
so--called Frisch scheme. This report decribes three
different estimation criteria within the Frisch context and
compares their estimation accuracy on the basis of the
asymptotic covariance matrices of the estimates. Some final
numerical examples support the theoretical results and
analyze the behaviour of the methods in case of finite
number of data.}
}
@TechReport{ it:2007-020,
author = {J. Nordstr{\"o}m and F. Ham and M. Shoeybi and E. van der
Weide and M. Sv{\"a}rd and K. Mattsson and G. Iaccarino and
J. Gong},
title = {A Hybrid Method for Unsteady Fluid Flow},
institution = it,
department = tdb,
year = 2007,
number = {2007-020},
month = aug,
abstract = {We show how a stable and accurate hybrid procedure for
fluid flow can be constructed. Two separate solvers, one
using high order finite difference methods and another
using the node-centered unstructured finite volume method
are coupled in a truly stable way. The two flow solvers run
independently and receive and send information from each
other by using a third coupling code. Exact solutions to be
Euler equations are used to verify the accuracy and
stability of the new computational procedure. We also
demonstrate the capability of the new procedure in a
calculation of the flow in and around a model of a coral.
}
}
@TechReport{ it:2007-019,
author = {Sofia Eriksson and Magnus Sv{\"a}rd and Jan Nordstr{\"o}m},
title = {Simulations of Ground Effects on Wake Vortices at
Runways},
institution = it,
department = tdb,
year = 2007,
number = {2007-019},
month = jun,
abstract = {In this paper the interaction between two counter-rotating
vortices is examined, and the performance of a newly
developed finite difference code is discussed. The Reynolds
numbers considered are low to medium, and the flow is
compressible. Most of the computations are performed in a
two dimensional domain, with different grid sizes, Reynolds
number and order of accuracy of the scheme. Finally, a
three dimensional computation is made in order to examine
the relevance of the two dimensional model.}
}
@TechReport{ it:2007-018,
author = {Robin Adams and Sally Fincher and Arnold Pears and Jonas
Boustedt and J{\"u}rgen B{\"o}rstler and Peter Dalenius and
Gunilla Eken and Tim Heyer and Andreas Jakobsson and Vanja
Lindberg and Bengt Molin and Jan Erik Mostr{\"o}m and
Mattias Wiggberg},
title = {What is the Word for ``Engineering'' in {S}wedish: Swedish
Students~ Conceptions of their Discipline},
institution = it,
year = 2007,
number = {2007-018},
month = jun,
abstract = {Engineering education in Sweden ~ as in the rest of the
world ~ is experiencing a decline in student interest.
There are concerns about the ways in which students think
about engineering education, why they join an academic
programme in engineering, and why they persist in their
studies. In this context the aims of the Nationellt
{\"a}mnesdidaktiskt Centrum f{\"o}r Teknikutbildning i
Studenternas Sammanhang project (CeTUSS) is to investigate
the student experience and to identify and support a
continuing network of interested researchers, as well as in
building capacity for disciplinary pedagogic investigation.
The Stepping Stones project brings together these interests
in a multi-researcher, multi-institutional study that
investigates how students and academic staff perceive
engineering in Sweden and in Swedish education. The first
results of that project are reported here. As this study is
situated uniquely in Swedish education, it allows for
exploration of ~a Swedish perspective~ on conceptions of
engineering. The Stepping Stones project was based on a
model of research capacity-building previously instantiated
in the USA and Australia (Fincher & Tenenberg, 2006). }
}
@TechReport{ it:2007-017,
author = {Olof Rensfelt and Lars-{\AA}ke Larzon},
title = {A Bandwidth Study of a {DHT} in a Heterogeneous
Environment},
institution = it,
department = docs,
year = 2007,
number = {2007-017},
month = may,
abstract = {We present a NS-2 implementation of a distributed hash
table (DHT) modeled after Bamboo. NS-2 is used to evaluate
the bandwidth costs involved in using a DHT in
heterogeneous environments. Networks are modeled as mixed
networks of desktop machines and 3G cellphones. We also
document the modifications of NS-2 that were needed to
simulate churn in large networks.}
}
@TechReport{ it:2007-016,
author = {Erik Nordstr{\"o}m and Per Gunningberg and Christian
Rohner and Oskar Wibling},
title = {A Cross-Environment Study of Routing Protocols for
Wireless Multi-hop Networks},
institution = it,
department = docs,
year = 2007,
number = {2007-016},
month = apr,
abstract = {We study ad hoc routing protocol mechanisms that impact
the performance during and after periods of connectivity
change. Our evaluation procedure is facilitated by using a
structured and tool-supported approach, combining real
world experiments with simulation and emulation. This
method enables us to find performance-critical time regions
in our traces. Our analysis shows that performance is
largely determined by how accurately a protocol senses
connectivity in these regions. Inaccurate sensing can
seriously affect the performance of the protocol, even
after the critical regions. We identify three significant
problems with sensing that we call
\emph{Self-interference}, \emph{TCP backlashing} and
\emph{Link cache poisoning}. We discuss their effect on the
design of sensing mechanisms in routing protocols and
suggest how the protocols can be made more robust.}
}
@TechReport{ it:2007-015,
author = {Torbj{\"o}rn Wigren},
title = {{MATLAB} Software for Recursive Identification of Systems
With Output Quantization ~ Revision 1},
institution = it,
department = syscon,
year = 2007,
number = {2007-015},
month = apr,
note = {The software package can be downloaded from
\url{http://www.it.uu.se/research/publications/reports/2007-015/QRISRev1.zip}}
,
abstract = {This reports is intended as a users manual for a package
of MATLAB scripts and functions, developed for recursive
identification of discrete time nonlinear Wiener systems,
where the static output nonlinearity is a known arbitrary
quantization function, not necessarily monotone. Wiener
systems consist of linear dynamics in cascade with a static
nonlinearity. Hence the systems treated by the software
package can also be described as discrete time linear
systems, where the output is measured after a known
quantization function. The identification algorithms thus
identify the linear dynamics of the Wiener system. The core
of the package is an implementation of 5 recursive SISO
output error identification algorithms. The measurement
noise is assumed to affect the system after quantization.
The identified linear dynamic part of the system is allowed
to be of FIR or IIR type. A key feature of the
identification algorithms is the use of a smooth
approximation of the quantizer, for derivation of an
approximation of the gradient of the algorithm. This is
necessary since the derivative of the quantizer consists of
a set of pulses, in the quantization steps. Using such an
approximation 2 recursive stochastic gradient algorithms
and 3 recursive Gauss-Newton algorithms are obtained. The
algorithms differ by the choice of gradient approximation.
It should be noted that the stochastic gradient algorithms
are primarily suited for (high order) FIR systems ~ they
converge very slowly for IIR systems due to the large
eigenvalue spread of the Hessian that typically results for
IIR systems. Arbitrarily colored additive measurement noise
is handled by all algorithms. The software can only be run
off-line, i.e. no true real time operation is possible. The
algorithms are however implemented so that true on-line
operation can be obtained by extraction of the main
algorithmic loops. The user must then provide the real time
environment. The software package contains scripts and
functions that allow the user to either input live
measurements or to generate test data by simulation. The
functionality for display of results include scripts for
plotting of data, parameters and prediction errors. Model
validation is supported by several methods apart from the
display functionality. First, calculation of the RPEM loss
function can be performed, using parameters obtained at the
end of an identification run. Pole-zero plots can be used
to investigate possible overparameterization in the linear
dynamic part of the Wiener model. Finally, the static
accuracy as a function of the output signal amplitude can
be assessed with mean residual analysis.}
}
@TechReport{ it:2007-014,
author = {Parosh Aziz Abdulla and Giorgio Delzanno and Ahmed
Rezine},
title = {Parameterized Verification of Infinite-state Processes
with Global Conditions},
institution = it,
department = docs,
year = 2007,
number = {2007-014},
month = apr,
note = {A short version of this paper will appear in the
proceedings of \emph{Computer Aided Verification} (CAV)
2007.},
abstract = {We present a simple and effective approximated backward
reachability algorithm for parameterized systems with
existentially and universally quantified global conditions.
The individual processes operate on unbounded local
variables ranging over the natural numbers. In addition,
processes may communicate via broadcast, rendez-vous and
shared variables. We apply the algorithm to verify mutual
exclusion for complex protocols such as Lamport's bakery
algorithm both with and without atomicity conditions, a
distributed version of the bakery algorithm, and
Ricart-Agrawala's distributed mutual exclusion algorithm.}
}
@TechReport{ it:2007-013,
author = {Torbj{\"o}rn Wigren and Linda Brus},
title = {{MATLAB} Software for Recursive Identification and Scaling
Using a Structured Nonlinear Black-box Model - Revision 3},
institution = it,
department = syscon,
year = 2007,
number = {2007-013},
month = apr,
note = {Revised version of nr 2005-022. The software package can
be downloaded from
\url{http://www.it.uu.se/research/publications/reports/2007-013/NRISoftwareRev3.zip}}
,
abstract = {This reports is intended as a users manual for a package
of MATLAB scripts and functions, developed for recursive
prediction error identification of nonlinear state space
systems and nonlinear static systems. The core of the
package is an implementation of an output error
identification and scaling algorithm. The algorithm is
based on a continuous time, structured black box state
space model of a nonlinear system. An RPEM algorithm for
recursive identification of nonlinear static systems, that
re-uses the parameterization of the nonlinear ODE model, is
also included in the software package. In this version of
the software an initialization algorithm based on Kalman
filter theory has been added to the package. The purpose of
the initialization algorithm is to find initial parameters
for the prediction error algorithm, and thus reduce the
risk of convergence to local minima for the nonlinear
identification problem. The software can only be run
off-line, i.e. no true real time operation is possible. The
algorithms are however implemented so that true on-line
operation can be obtained by extraction of the main
algorithmic loop. The user must then provide the real time
environment. The software package contains scripts and
functions that allow the user to either input live
measurements or to generate test data by simulation. The
scripts and functions for the setup and execution of the
identification algorithms are somewhat more general than
what is described in the references. There is e.g. support
for automatic re-initiation of the algorithms using the
parameters obtained at the end of a previous identification
run. This allows for multiple runs through a set of data,
something that is useful for data sets that are too short
to allow convergence in a single run. The re-initiation
step also allows the user to modify the degrees of the
polynomial model structure and to specify terms that are to
be excluded from the model. This makes it possible to
iteratively re-fine the estimated model using multiple
runs. The functionality for display of results include
scripts for plotting of data, parameters, prediction
errors, eigenvalues and the condition number of the
Hessian. The estimated model obtained at the end of a run
can be simulated and the model output plotted, alone or
together with the data used for identification. Model
validation is supported by two methods apart from the
display functionality. First, a calculation of the RPEM
loss function can be performed, using parameters obtained
at the end of an identification run. Secondly, the accuracy
as a function of the output signal amplitude can be
assessed.}
}
@TechReport{ it:2007-012,
author = {Alexander Churilov and Alexander Medvedev and Alexander
Shepeljavyi},
title = {Mathematical Model of Non-Basal Testosterone Regulation in
the Male by Pulse Modulated Feedback},
institution = it,
department = syscon,
year = 2007,
number = {2007-012},
month = apr,
abstract = {A parsimonious mathematical model of pulse modulated
regulation of non-basal testosterone secretion in the male
is developed. The model is of third differential order,
reflecting the three most significant hormones in the
regulation loop, but is yet shown to be capable of
sustaining periodic solutions with one or two pulses of
gonadotropin-releasing hormone (GnRH) on each period. Lack
of stable periodic solutions is otherwise a main
shortcoming of existing low-order hormone regulation
models. Existence and stability of periodic solutions are
studied. The periodic mode with two GnRH pulses on the
least period has not been described in medical literature
but is found to explain experimental data well. }
}
@TechReport{ it:2007-011,
author = {Lars Ferm and Per L{\"o}tstedt and Andreas Hellander},
title = {A Hierarchy of Approximations of the Master Equation
Scaled by a Size Parameter},
institution = it,
department = tdb,
year = 2007,
number = {2007-011},
month = apr,
abstract = {Solutions of the master equation are approximated using a
hierarchy of models based on the solution of ordinary
differential equations: the macroscopic equations, the
linear noise approximation and the moment equations. The
advantage with the approximations is that the computational
work with deterministic algorithms grows as a polynomial in
the number of species instead of an exponential growth with
conventional methods for the master equation. The relation
between the approximations is investigated theoretically
and in numerical examples. The solutions converge to the
macroscopic equations when a parameter measuring the size
of the system grows. A computational criterion is suggested
for estimating the accuracy of the approximations. The
numerical examples are models for the migration of people,
in population dynamics and in molecular biology.}
}
@TechReport{ it:2007-010,
author = {Torbj{\"o}rn Wigren},
title = {{MATLAB} software for Recursive Identification of Wiener
Systems - Revision 2},
institution = it,
department = syscon,
year = 2007,
number = {2007-010},
month = mar,
note = {The software package was updated to handle FIR systems,
revision 3, April 2007. The updated software package and
manual can be downloaded from
\url{http://www.it.uu.se/research/publications/reports/2007-010/WRIS.zip}}
,
abstract = {This reports is intended as a users manual for a package
of MATLAB scripts and functions, developed for recursive
prediction error identification of discrete time nonlinear
Wiener systems and nonlinear static systems. Wiener systems
consist of linear dynamics in cascade with a static
nonlinearity. The core of the package is an implementation
of 9 recursive SISO output error identification algorithms.
Three main cases are treated. The first set of 5 algorithms
identify the IIR linear dynamics in cases where the static
nonlinearity is known. It is stressed that the nonlinearity
is allowed to be non-invertible. The second set of 2
algorithms simultaneously identifies the linear dynamics
and the static non-linearity. The nonlinearity is
parameterized as a piecewise linear or a piecewise
quadratic nonlinear function. The last set of two
algorithms exploits the above parameterization of the
static nonlinearity for estimation of static nonlinear
systems. Arbitrarily colored additive measurement noise is
handled by all algorithms. The software can only be run
off-line, i.e. no true real time operation is possible. The
algorithms are however implemented so that true on-line
operation can be obtained by extraction of the main
algorithmic loops. The user must then provide the real time
environment. The software package contains scripts and
functions that allow the user to either input live
measurements or to generate test data by simulation. The
functionality for display of results include scripts for
plotting of data, parameters and prediction errors. Model
validation is supported by several methods apart from the
display functionality. First, calculation of the RPEM loss
function can be performed, using parameters obtained at the
end of an identification run. Pole-zero plots can be used
to investigate possible overparameterization in the linear
dynamic part of the Wiener model. Finally, the static
accuracy as a function of the output signal amplitude can
be assessed.}
}
@TechReport{ it:2007-009,
author = {Magnus {\AA}gren and Pierre Flener and Justin Pearson},
title = {On Constraint-Oriented Neighbours for Local Search},
institution = it,
department = csd,
year = 2007,
number = {2007-009},
month = mar,
abstract = {In the context of local search, we investigate the
exploration of constraint-oriented neighbourhoods, where a
set of constraints is picked before considering the
neighbouring configurations where those constraints may
have a different penalty. Given the semantics of a
constraint, neighbourhoods consisting only of
configurations with decreased (or preserved, or increased)
penalty can be represented intensionally as a new attribute
for constraint objects. We present a framework for
combining neighbourhoods that allows different local search
heuristics to be expressed, including multi-phase
heuristics where an automatically identifiable suitable
subset of the constraints is satisfied upon a first phase
and then preserved in a second phase. This simplifies the
design of local search algorithms compared to using just a
variable-oriented neighbourhood, while not incurring any
runtime overhead.}
}
@TechReport{ it:2007-008,
author = {Erik B{\"a}ngtsson and Maya Neytcheva},
title = {Finite Element Block-Factorized Preconditioners},
institution = it,
department = tdb,
year = 2007,
number = {2007-008},
month = mar,
abstract = {In this work we consider block-factorized preconditioners
for the iterative solution of systems of linear algebraic
equations arising from finite element discretizations of
scalar and vector partial differential equations of
elliptic type.
For the construction of the preconditioners we utilize a
general two-level standard finite element framework and the
corresponding block two-by-two form of the system matrix,
induced by a splitting of the finite element spaces,
referred to as {\em fine} and {\em coarse}, namely, $$ A =
\begin{bmatrix} A_{11}&A_{12}\\ A_{21}&A_{22}\end{bmatrix}
\begin{matrix}fine,\\ coarse.\end{matrix}. $$ The matrix
$A$ admits the exact factorization $$ A =
\begin{bmatrix}A_{11}&0\\ {A}_{21}&{S_A}\end{bmatrix}
\begin{bmatrix}I_{1}&A_{11}^{-1}A_{12}\\ 0&
I_2\end{bmatrix}, $$ where
$S_A=A_{22}-A_{21}A_{11}^{-1}A_{12}$ and $I_1$, $I_2$ are
identity matrices of corresponding size. The particular
form of preconditioners we analyze here is $$ M_{B} =
\begin{bmatrix}B_{11}&0\\ {A}_{21}&{S}\end{bmatrix}
\begin{bmatrix}I_{1}&Z_{12}\\ 0& I_2\end{bmatrix}, $$ where
$S$ is assumed to be some available good quality
approximation of the Schur complement matrix $S_A$.
We propose two methods to construct an efficient, sparse
and computationally cheap approximation $B_{11}^{-1}$ of
the inverse of the pivot block $A_{11}^{-1}$, required when
solving systems with the block factorized preconditioner
$M_B$. Furthermore, we propose an approximation $Z_{12}$ of
the off-diagonal matrix block product $A_{11}^{-1}A_{12}$,
which further reduces the computational complexity of the
preconditioning step. All three approximations are based on
element-by-element manipulations of local finite element
matrices.
The approach is applicable for both selfadjoint and
non-selfadjoint problems, in two as well as in three
dimensions. We analyze in detail the 2D case and provide
extensive numerical evidence for the efficiency of the
proposed matrix approximations.}
}
@TechReport{ it:2007-007,
author = {Malin Ljungberg},
title = {Composable Difference Operators for Coordinate Invariant
Partial Differential Equations},
institution = it,
department = tdb,
year = 2007,
number = {2007-007},
month = feb,
abstract = {Computer simulations are a cost efficient complement to
laboratory experiments. Software for the solution of
partial differential equations is part of the basic
infrastructure for the evolving field of Computational
Science and Engineering. Numerical analysts are involved in
the development of suitable methods and algorithms for the
solution of a wide range of partial differential equations.
Based on the needs of a numerical analyst, we here identify
requirements on software for the solution of partial
differential equations. In particular, we look at support
for flexible formulations of finite difference methods on
curvilinear structured grids.
We present FlexOp, a software solution that meets the
requirements that have been identified. The semantics of
the FlexOp is highly mathematical, and includes coordinate
invariant operators. The discretization strategy is
specified using parameterized classes, and can be chosen
independently for different instances of the same operator.
The use of static polymorphism allows for a flexible and
efficient implementation of the application of the
discretized operator.
In order to assess the FlexOp, we use them to implement a
compact fourth-order Numerov method, using the
\textsc{TENGOME} infrastructure as a basis and C++ as the
implementation language.
We find that the FlexOp are easy to use, because of the
high agreement between mathematical derivation and
implementation of the method. Compared with a special
purpose implementation for a particular discretization
scheme, we find that FlexOp offer a significant reduction
in the number of lines of code, together with an associated
enhanced maintainability. The increased flexibility comes
without a cost in the form of an increase of execution
time, when compared with the special purpose application. }
}
@TechReport{ it:2007-006,
author = {Anders Berglund and Mattias Wiggberg (eds.)},
title = {Proceedings from the 6th Baltic Sea Conference in
Computing Education Research, Koli Calling},
institution = it,
department = docs,
year = 2007,
number = {2007-006},
month = feb,
abstract = {The 6th Baltic Sea Conference on Computing Education
Research, Koli Calling, aims to promote the exchange of
relevant research contributions and practical information
between colleagues in the international community of
Computing Education Research. Furthermore, Koli Calling
aims to combine teaching and learning experiences that have
a solid, theoretically anchored research orientation.
The conference took place in the inspiring surroundings of
the Koli National Park in Eastern Finland, November 9th -
12th 2006, and was organized by Uppsala University, Sweden
with local arrangements by University of Joensuu. The
submissions were double blind reviewed by the international
program committee. Accepted papers are published in these
final proceedings and are also available in the ACM Digital
Library.}
}
@TechReport{ it:2007-005,
author = {Parosh Aziz Abdulla and Ben Henda, Noomene and Richard
Mayr and Sven Sandberg and de Alfaro, Luca},
title = {Stochastic Games with Lossy Channels},
institution = it,
department = docs,
year = 2007,
number = {2007-005},
month = feb,
note = {Updated 14 December 2007. To appear in the proceedings of
FoSSaCS 2008.},
abstract = {We consider turn-based stochastic games on infinite graphs
induced by game probabilistic lossy channel systems
(GPLCS), the game version of probabilistic lossy channel
systems (PLCS). We study games with Buchi (repeated
reachability) objectives and almost-sure winning condition.
Under the assumption that the target set is regular, a
symbolic representation of the set of winning states for
each player can be effectively constructed. Thus,
turn-based stochastic games on GPLCS are decidable. This
generalizes earlier decidability result for PLCS-induced
Markov decision processes. Our scheme can be adapted to
GPLCS with simple reachability objectives.},
oldabstract = {We consider turn-based stochastic games on infinite graphs
induced by game probabilistic lossy channel systems
(GPLCS), the game version of probabilistic lossy channel
systems (PLCS). We study games with B{\"u}chi (repeated
reachability) objectives and almost-sure winning condition.
Under the condition that the players are limited to
finite-memory strategies, a symbolic representation of the
set of winning states for each player can be effectively
constructed. Thus, finite-memory turn-based stochastic
games on GPLCS are decidable. This generalizes a
decidability result on finite-memory schedulers for
PLCS-induced Markov decision processes in [C. Baier, N.
Bertrand, P. Schnoebelen. Verifying nondeterministic
probabilistic channel systems against $\omega$-regular
linear-time properties. {\it ACM Transactions on Comp.
Logic}, 2006. To appear.]. Our scheme can be adapted to
GPLCS with simple reachability objectives.}
}
@TechReport{ it:2007-004,
author = {Jonas Persson},
title = {Pricing American Options Using a Space-time Adaptive
Finite Difference Method},
institution = it,
department = tdb,
year = 2007,
number = {2007-004},
month = jan,
abstract = {American options are priced numerically using a space- and
time-adaptive finite difference method. The generalized
Black-Scholes operator is discretized on a Cartesian
structured but non-equidistant grid in space. The space-
and time-discretizations are adjusted such that a
predefined tolerance level on the local discretization
error is met. An operator splitting technique is used to
separately handle the early exercise constraint and the
solution of linear systems of equations from the finite
difference discretization of the linear complementarity
problem. In numerical experiments three variants of the
adaptive time-stepping algorithm with and without local
time-stepping are compared.}
}
@TechReport{ it:2007-003,
author = {Pierre Flener and Justin Pearson and Magnus {\AA}gren and
Carlos Garcia Avello and Mete \c{C}eliktin},
title = {Air-Traffic Complexity Resolution in Multi-Sector
Planning},
institution = it,
department = csd,
year = 2007,
number = {2007-003},
month = jan,
abstract = {Using constraint programming, we effectively model and
efficiently solve the problem of balancing and minimising
the traffic complexities of an airspace of adjacent
sectors. The traffic complexity of a sector is here defined
in terms of the numbers of flights within it, near its
border, and on non-level segments within it. The allowed
forms of complexity resolution are the changing of the
take-off times of not yet airborne flights, the changing of
the remaining approach times into the chosen airspace of
already airborne flights by slowing down and speeding up
within the two layers of feeder sectors around that
airspace, as well as the changing of the levels of passage
over way-points in that airspace. Experiments with actual
European flight profiles obtained from the Central Flow
Management Unit (CFMU) show that these forms of complexity
resolution can lead to significant complexity reductions
and rebalancing. }
}
@TechReport{ it:2007-002,
author = {Jing Gong and Jan Nordstr{\"o}m},
title = {A Stable and Efficient Hybrid Scheme for Viscous Problems
in Complex Geometries},
institution = it,
department = tdb,
year = 2007,
number = {2007-002},
month = jan,
abstract = {In this paper we present a stable hybrid scheme for
viscous problems. The hybrid method combines the
unstructured finite volume method with high-order finite
difference methods on complex geometries.
The coupling procedure between the two numerical methods is
based on energy estimates and stable interface conditions
are constructed. Numerical calculations show that the
hybrid method is efficient and accurate. }
}
@TechReport{ it:2006-052,
author = {Parosh Aziz Abdulla and Noomene Ben Henda and Giorgio
Delzanno and Ahmed Rezine},
title = {Regular Model Checking without Transducers (On Efficient
Verification of Parameterized Systems)},
institution = it,
department = docs,
year = 2006,
number = {2006-052},
month = dec,
note = {To appear in the proceedings of TACAS 2007},
abstract = {We give a simple and efficient method to prove safety
properties for parameterized systems with linear
topologies. A process in the system is a finite-state
automaton, where the transitions are guarded by both local
and global conditions. Processes may communicate via
broadcast, rendez-vous and shared variables. The method
derives an over-approximation of the induced transition
system, which allows the use of a simple class of regular
expressions as a symbolic representation. Compared to
traditional regular model checking methods, the analysis
does not require the manipulation of transducers, and hence
its simplicity and efficiency. We have implemented a
prototype which works well on several mutual exclusion
algorithms and cache coherence protocols.}
}
@TechReport{ it:2006-051,
author = {Erik B{\"a}ngtsson and Bj{\"o}rn Lund},
title = {A Comparison Between Two Solution Techniques to Solve the
Equations of Linear Isostasy},
institution = it,
department = tdb,
year = 2006,
number = {2006-051},
month = dec,
abstract = {In this paper we compare two models to compute the
isostatic response of the Earths lithosphere to an external
load. The lithosphere is modeled as a linear elastic solid.
The two models differ in the mathematical formulation of
the problem, their applicability in the incompressible
limit, the choice of the finite elements used for
discretization, and the solution strategy for the arising
algebraic problem. The efficiency and accuracy of both
models are compared via extensive numerical experiments in
2D and 3D.}
}
@TechReport{ it:2006-050,
author = {Iordanis Kavathatzopoulos},
title = {AvI-enk{\"a}ten: Ett verktyg f{\"o}r att m{\"a}ta
anv{\"a}ndbarhet, stress och nytta av IT-st{\"o}d},
institution = it,
department = hci,
year = 2006,
number = {2006-050},
month = dec,
note = {In Swedish},
abstract = {Syftet med detta arbete {\"a}r att utveckla ett index
f{\"o}r att beskriva anv{\"a}ndbarheten hos IT-verktyg och
hur anv{\"a}ndbarhet p{\aa}verkar effektivitet. Enk{\"a}ten
pr{\"o}vades inom CSN och g{\"a}llde IT-verktyget STIS2000.
498 personer svarade p{\aa} enk{\"a}ten, 68\% av alla
anv{\"a}ndare av verktyget. Sammanh{\aa}llningen av
enk{\"a}tens delar och fr{\aa}gor {\"a}r
tillfredsst{\"a}llande. Tillf{\"o}rlitligheten {\"a}r
ocks{\aa} tillfredsst{\"a}llande. Enk{\"a}tens struktur och
inneh{\aa}ll utg{\"o}r en bra grund f{\"o}r att konstruera
ett anv{\"a}ndbarhetsindex. Svaren visar ocks{\aa} att
deltagarna {\"a}r ganska positiva n{\"a}r det g{\"a}ller
anv{\"a}ndningen av STIS2000 inom CSN.}
}
@TechReport{ it:2006-049,
author = {Stefan Blomkvist},
title = {The User as a Personality: A Reflection on the Theoretical
and Practical Use of Personas in {HCI} Design},
institution = it,
department = hci,
year = 2006,
number = {2006-049},
month = nov,
abstract = {A persona is a user model that focuses on the individual's
goals in interaction. The model resembles classical user
profiles, but with some important distinctions. The persona
represents patterns of users' behaviour and goals. The
concept has a focus on practical interaction design and is
not based on a theoretical HCI perspective, although it
implies a distinctive perspective on the role of users and
interaction. The purpose of this paper is to examine how
this concept relates to some theoretical perspectives on
users and interaction. One such theory that I discuss is
activity theory, which share the emphasis on that
interaction is driven by users' motives and goals. But
activity theory is a more elaborated framework for studying
activities. The conclusion is that personas have a narrower
perspective on users and activities compared to activity
theory, but this also makes it more easy to use as a tool
to direct design. Also, the role of the user in the persona
approach is blurred with the role as a consumer. The issue
of interaction design becomes a matter of satisfying the
needs of the consumers, not to improve human work and life.
}
}
@TechReport{ it:2006-048,
author = {Owe Axelsson and Radim Blaheta and Maya Neytcheva},
title = {Preconditioning of Boundary Value Problems using
Elementwise {S}chur Complements},
institution = it,
department = tdb,
year = 2006,
number = {2006-048},
month = nov,
abstract = {Based on a particular node ordering and corresponding
block decomposition of the matrix we analyse an efficient,
algebraic multilevel preconditioner for the iterative
solution of finite element discretizations of elliptic
boundary value problems. Thereby an analysis of a new
version of block-factorization preconditioning methods is
presented. The approximate factorization requires an
approximation of the arising Schur complement matrix. In
this paper we consider such approximations derived by the
assembly of the local macro-element Schur complements.
The method can be applied also for non-selfadjoint problems
but for the derivation of condition number bounds we assume
that the corresponding differential operator is selfadjoint
and positive definite.}
}
@TechReport{ it:2006-047,
author = {Henrik Johansson and Johan Steensland},
title = {A Performance Characterization of Load Balancing
Algorithms for Parallel {SAMR} Applications},
institution = it,
department = tdb,
year = 2006,
number = {2006-047},
month = oct,
abstract = {We perform a comprehensive performance characterization of
load balancing algorithms for parallel structured adaptive
mesh refinement (SAMR) applications. Using SAMR,
computational resources are dynamically concentrated to
areas in need of a high accuracy. Because of the dynamic
resource allocation, the workload must repeatedly be
partitioned and distributed over the processors. For an
efficient parallel SAMR implementation, the partitioning
algorithm must be dynamically selected at run-time with
regard to both the application and computer state. We
characterize and compare a common partitioning algorithm
and a large number of alternative partitioning algorithms.
The results prove the viability of dynamic algorithm
selection and show the benefits of using a large number of
complementing partitioning algorithms. }
}
@TechReport{ it:2006-046,
author = {Mei Hong and Torsten S{\"o}derstr{\"o}m and Wei Xing Zheng},
title = {Asymptotic Accuracy Analysis of Bias-Eliminating Least
Squares Estimates for Identification of Errors in Variables
Systems},
institution = it,
department = syscon,
year = 2006,
number = {2006-046},
month = oct,
abstract = {The bias-eliminating least squares (BELS) method is one of
the consistent estimators for identifying dynamic
errors-in-variables systems. The attraction of the BELS
method lies in its good accuracy and its modest
computational cost. In this report, we investigate the
asymptotic accuracy properties of the BELS estimates. It is
shown that the estimated system parameters and the
estimated noise variances are asymptotically Gaussian
distributed. An explicit expression for the normalized
covariance matrix of the estimated parameters is derived
and supported by some numerical examples.}
}
@TechReport{ it:2006-045,
author = {Anders Hessel and Paul Pettersson},
title = {Model-Based Testing of a {WAP} Gateway: an Industrial
Case-Study},
institution = it,
department = docs,
year = 2006,
number = {2006-045},
month = sep,
abstract = {We present experiences from a case study where a
model-based approach to black-box testing is applied to
verify that a Wireless Application Protocol (WAP) gateway
conforms to its specification. The WAP gateway is developed
by Ericsson and used in mobile telephone networks to
connect mobile phones with the Internet. We focus on
testing the software implementing the session (WSP) and
transaction (WTP) layers of the WAP protocol. These layers,
and their surrounding environment, are described as a
network of timed automata. To model the many sequence
numbers (from a large domain) used in the protocol, we
introduce an abstraction technique. We believe the
suggested abstraction technique will prove useful to model
and analyse other similar protocols with sequence numbers,
in particular in the context of model-based testing.
A complete test bed is presented, which includes generation
and execution of test cases. It takes as input a model and
a coverage criterion expressed as an observer, and returns
a verdict for each test case. The test bed includes
existing tools from Ericsson for test-case execution. To
generate test suites, we use our own tool \textsc{Cover}
--- a new test-case generation tool based on the real-time
model-checker \textsc{Uppaal}.}
}
@TechReport{ it:2006-044,
author = {Mei Hong and Torsten S{\"o}derstr{\"o}m and Johan
Schoukens and Rik Pintelon},
title = {Comparison of Time Domain Maximum Likelihood Method and
Sample Maximum Likelihood Method in Errors-in-Variables
Identification},
institution = it,
department = syscon,
year = 2006,
number = {2006-044},
month = sep,
abstract = {The time domain maximum likelihood (TML) method and the
Sample Maximum Likelihood (SML) method are two general
approaches for identifying errors-in-variables models. In
the TML method, an important assumption is that the
noise-free input signal must be a stationary process with
rational spectrum. For SML, the noise-free input need to be
periodic. In this report, numerical comparisons of these
two methods are done under different situations. The
results suggest that TML and SML have similar estimation
accuracy at moderate or high signal-to-noise ratio (SNR).}
}
@TechReport{ it:2006-043,
author = {Jarmo Rantakokko},
title = {Case-Centered Learning of Scientific Computing},
institution = it,
department = tdb,
year = 2006,
number = {2006-043},
month = sep,
abstract = {Traditionally courses in scientific computing teach a
large number of methods and algorithms for different
mathematical problems. The algorithms are applied on
simplified problems and not on real applications. The
result is that the students can't see the main thread, they
focus only on the details of the methods and don't see the
entirety. The students can not put what they learn into
perspective and their motivation to study becomes
diminished. In this paper we suggest a case-centered
approach for learning scientific computing. We use a
real-life case, weather prediction, as a starting point for
learning. The case is analyzed and discussed in class. To
follow up the discussions the students are assigned
learning tasks in scientific computing defined from the
case analysis. The real-life application connects the
different topics in scientific computing together and
motivates the students. The response from the students has
been positive and the case has increased their
understanding of what scientific computing is and what it
can be used for.}
}
@TechReport{ it:2006-042,
author = {Eddie Wadbro},
title = {On the Far-Field Properties of an Acoustic Horn},
institution = it,
department = tdb,
year = 2006,
number = {2006-042},
month = sep,
abstract = {This report presents a derivation of an expression for
time harmonic acoustic wave propagation in the far field
for two and three space dimensions, and includes detailed
descriptions of the numerical evaluation of the far-field
pattern in some typical situations. The presentation covers
all parts required for computing the far-field properties
of acoustical devices, and the report is designed to
function as a single reference for these computations.}
}
@TechReport{ it:2006-041,
author = {Markus Nord{\'e}n},
title = {Performance Modelling for Parallel {PDE} Solvers on
{NUMA}-Systems},
institution = it,
department = tdb,
year = 2006,
number = {2006-041},
month = aug,
abstract = {A detailed model of the memory performance of a PDE solver
running on a NUMA-system is set up. Due to the complexity
of modern computers, such a detailed model inevitably is
very complicated. Therefore, approximations are introduced
that simplify the model and allows NUMA-systems and PDE
solvers to be described conveniently.
Using the simplified model, it is shown that PDE solvers
using ordered local methods can be made very unsensitive to
high NUMA-ratios, allowing them to scale well on virtually
any NUMA-system.
PDE solvers using unordered local methods, semiglobal
methods or global methods are more sensitive to high
NUMA-ratios and require special techniques in order to
scale well beyond a single locality group.
Nevertheless, the potential performance gain of improving
the data distribution on a NUMA-system can be considerable
for all kinds of PDE solvers studied. }
}
@TechReport{ it:2006-040,
author = {Mei Hong and Torsten S{\"o}derstr{\"o}m and Wei Xing Zheng},
title = {A Simplified Form of the Bias-Eliminating Least Squares
Method for Errors-In-Variables Identification},
institution = it,
department = syscon,
year = 2006,
number = {2006-040},
month = aug,
abstract = {This report considers the bias-eliminating least squares
(BELS) method for identifying the errors-in-variables
systems with white input noise and colored output noise. A
simplified form of the BELS algorithm is proposed which is
proved to be equivalent to the existing one. The new
relation is a form of linear IV equations which will not
only reduce the computational load but also simplify the
analysis of the properties of the BELS estimates.}
}
@TechReport{ it:2006-039,
author = {Andreas Hellander and Per L{\"o}tstedt},
title = {Hybrid Method for the Chemical Master Equation},
institution = it,
department = tdb,
year = 2006,
number = {2006-039},
month = aug,
abstract = {The chemical master equation is solved by a hybrid method
coupling a macroscopic, deterministic description with a
mesoscopic, stochastic model. The molecular species are
divided into one subset where the expected values of the
number of molecules are computed and one subset with
species with a stochastic variation in the number of
molecules. The macroscopic equations resemble the reaction
rate equations and the probability distribution for the
stochastic variables satisfy a master equation. The
probability distribution is obtained by the Stochastic
Simulation Algorithm due to Gillespie. The equations are
coupled via a summation over the mesoscale variables. This
summation is approximated by Monte Carlo and Quasi Monte
Carlo methods. The error in the approximations is analyzed.
The hybrid method is applied to three chemical systems from
molecular cell biology.}
}
@TechReport{ it:2006-038,
author = {Markus Nord{\'e}n and Henrik L{\"o}f and Jarmo Rantakokko
and Sverker Holmgren},
title = {Geographical Locality and Dynamic Data Migration for
{OpenMP} Implementations of Adaptive {PDE} Solvers},
institution = it,
department = tdb,
year = 2006,
number = {2006-038},
month = aug,
note = {To appear in \emph{Proceedings of the 2:nd International
Workshop on OpenMP (IWOMP)}},
abstract = {On cc-NUMA multi-processors, the non-uniformity of main
memory latencies motivates the need for co-location of
threads and data. We call this special form of data
locality, \emph{geographical locality}. In this article, we
study the performance of a parallel PDE solver with
adaptive mesh refinement. The solver is parallelized using
OpenMP and the adaptive mesh refinement makes dynamic load
balancing necessary. Due to the dynamically changing memory
access pattern caused by the runtime adaption, it is a
challenging task to achieve a high degree of geographical
locality.
The main conclusions of the study are: (1) that
geographical locality is very important for the performance
of the solver, (2) that the performance can be improved
significantly using dynamic page migration of misplaced
data, (3) that a migrate-on-next-touch directive works well
whereas the first-touch strategy is less advantageous for
programs exhibiting a dynamically changing memory access
patterns, and (4) that the overhead for such migration is
low compared to the total execution time.}
}
@TechReport{ it:2006-037,
author = {Elisabeth Larsson and Krister {\AA}hlander and Andreas
Hall},
title = {Multi-Dimensional Option Pricing using Radial Basis
Functions and the Generalized {F}ourier Transform},
institution = it,
department = tdb,
year = 2006,
number = {2006-037},
month = aug,
abstract = {We show that the generalized Fourier transform can be used
for reducing the computational cost and memory requirements
of radial basis function methods for multi-dimensional
option pricing. We derive a general algorithm, including a
transformation of the Black--Scholes equation into the heat
equation, that can be used in any number of dimensions.
Numerical experiments in two and three dimensions show that
the gain is substantial even for small problem sizes.
Furthermore, the gain increases with the number of
dimensions.}
}
@TechReport{ it:2006-036,
author = {Stefan Engblom},
title = {A Discrete Spectral Method for the Chemical Master
Equation},
institution = it,
department = tdb,
year = 2006,
number = {2006-036},
month = jun,
note = {Superseded by report nr 2008-005},
abstract = {As an equivalent formulation of the Markov-assumption of
stochastic processes, the master equation of chemical
reactions is an accurate description of general systems in
chemistry. For $D$ reacting species this is a
differential-difference equation in $D$ dimensions, exactly
soluble for very simple systems only.
We present and analyze a novel solution strategy in the
form of a Galerkin spectral method with an inherent natural
adaptivity and a very favorable choice of basis functions.
The method is exemplified by the numerical solution of two
systems taken from molecular biology. It is shown that the
method remains effective and accurate when other
traditional solution methods produce less useful results.
}
}
@TechReport{ it:2006-035,
author = {Owe Axelsson and Janos Kar\'{a}tson},
title = {Mesh Independent Superlinear {PCG} Rates via
Compact-Equivalent Operators},
institution = it,
department = tdb,
year = 2006,
number = {2006-035},
month = jun,
abstract = {The subject of the paper is the mesh independent
convergence of the preconditioned conjugate gradient method
for nonsymmetric elliptic problems. The approach of
equivalent operators is involved, in which one uses the
discretization of another suitable elliptic operator to
construct a preconditioning matrix. By introducing the
notion of compact-equivalent operators, it is proved that
for a wide class of elliptic problems the superlinear
convergence of the obtained PCGM is mesh independent under
FEM discretizations, that is, the rate of superlinear
convergence is given in the form of a sequence which is
mesh independent and is determined only by the elliptic
operators.}
}
@TechReport{ it:2006-034,
author = {Agnes Rensfelt and Torsten S{\"o}derstr{\"o}m},
title = {Optimal Excitation for Nonparametric Identification of
Viscoelastic Materials},
institution = it,
department = syscon,
year = 2006,
number = {2006-034},
month = jun,
abstract = {The problem of optimal excitation in nonparametric
identification of viscoelastic materials is considered. The
goal is to design the input spectrum in an optimal way, so
that the average variance of the estimates is minimized. It
is shown how the covariance matrix of the estimates can be
expressed in terms of the input spectrum. This theory can
also be used in order to identify the (unknown) excitation,
used in a particular experiment, from measured strain data.
Two scalar criteria connected to A- and D-optimal
experiment design, are considered. The results indicate
that the accuracy of the estimates can be greatly improved
by applying an optimal input signal. Issues concerning the
implementation of the achieved optimal input spectrum in
live experiments are discussed briefly.}
}
@TechReport{ it:2006-033,
author = {Parosh Aziz Abdulla and Noomene Ben Henda and Richard Mayr
and Sven Sandberg},
title = {Limiting Behavior of {M}arkov Chains with Eager
Attractors},
institution = it,
department = docs,
year = 2006,
number = {2006-033},
month = jun,
abstract = {We consider discrete infinite-state Markov chains which
contain an eager finite attractor. A finite attractor is a
finite subset of states that is eventually reached with
probability 1 from every other state, and the eagerness
condition requires that the probability of avoiding the
attractor in $n$ or more steps after leaving it is
exponentially bounded in $n$. Examples of such Markov
chains are those induced by probabilistic lossy channel
systems and similar systems. We show that the expected
residence time (a generalization of the steady state
distribution) exists for Markov chains with eager
attractors and that it can be effectively approximated to
arbitrary precision. Furthermore, arbitrarily close
approximations of the limiting average expected reward,
with respect to state-based bounded reward functions, are
also computable. }
}
@TechReport{ it:2006-032,
author = {Torsten S{\"o}derstr{\"o}m},
title = {Extending the {F}risch Scheme for Errors-in-Variables
Identification to Correlated Output Noise},
institution = it,
department = syscon,
year = 2006,
number = {2006-032},
month = jun,
abstract = {Several estimation methods have been proposed for
identifying errors-in-variables systems, where both input
and output measurements are corrupted by noise. One of the
promising approaches is the so called Frisch scheme. In its
standard form it is designed to handle white measurement
noise on the input and output sides. As the output noise
comprises both effects of measurement errors and of process
disturbances, it is much more realistic to allow correlated
output noise. It is described in the paper how the Frisch
scheme can be extended to such cases. }
}
@TechReport{ it:2006-031,
author = {H{\aa}kan Zeffer and Erik Hagersten},
title = {A Case for Low-Complexity Multi-{CMP} Architectures},
institution = it,
department = docs,
year = 2006,
number = {2006-031},
month = jun,
abstract = {The advances in semiconductor technology have set the
shared memory server trend towards processors with multiple
cores per die and multiple threads per core. This paper
presents simple hardware primitives enabling flexible and
low complexity multi-chip designs supporting an efficient
inter-node coherence protocol run in software. The design
is based on two node permission bits per cache line and a
new way to decouple the intra-chip coherence protocol from
the inter-node coherence protocol. The protocol
implementation enables the system to cache remote data in
the local memory system with no additional hardware support.
Our evaluation is based on detailed full system simulation
of both commercial and HPC workloads. We compare a
low-complexity system based on the proposed primitives with
aggressive hardware multi-chip shared-memory systems and
show that the performance is competitive, and often better,
across a large design space.}
}
@TechReport{ it:2006-030,
author = {Lars-Henrik Eriksson},
title = {The {GTO} Toolset and Method},
institution = it,
department = csd,
year = 2006,
number = {2006-030},
month = jun,
abstract = {A suitable method supported by a toolset with a high
degree of automation is a necessity for the successful
employment of formal methods in industrial projects. The
GTO toolset and method have been developed, and
successfully applied, to formal methods in safety- critical
control applications related to railway signalling since
the mid 1990s.
The toolset and method support the entire formal methods
process from writing and validating formal specifications,
through modelling of the implementation to formal
verification and analysis of verification results. One goal
the toolset and method was to make formal methods more
competitive by streamlining the process so that -- at least
within an established application area -- individual
verification tasks could be done in an ``assembly
line''-like fashion with minimum overhead.
In line with this goal, the toolset is intended for use
with configurable systems, where a generic specification is
applicable to a family of systems and adapted to a specific
system using configuration data.
The functions carried out by the toolset include static
checking and simulation of specifications, checking of
configuration data, generation of implementation models
from PLC program code or relay schematics, simulation of
the implementation model, formal verification by refinement
proof, and analysis of failed refinement proofs. Refinement
proofs are automatically carried out by a satisfiability
(SAT) solver of the user's choice, which is interfaced to
the main tool.
We will outline the method and functions of the toolset as
well as the formal notation -- a simple temporal predicate
logic -- used by the toolset.}
}
@TechReport{ it:2006-029,
author = {Lars-Henrik Eriksson},
title = {Use of Domain Theories in Applied Formal Methods},
institution = it,
department = csd,
year = 2006,
number = {2006-029},
month = jun,
abstract = {A formal theory of an application domain can serve a key
role in formal specification and verification of systems
operating in that domain. This is particularly relevant
when working with families of similar systems intended to
control some kind of industrial process or function where
the control principles are general while the specifics of
the system depend on the particular installation the system
is intended to control. In such situations a domain theory
can facilitate writing generic specifications or
implementations for the entire family of systems which can
then be configured for each particular installation. Use of
concepts defined in the domain theory can also facilitate
communication with domain experts without knowledge in
formal methods.
An example of such a family is railway signalling systems
which all implement the same general signalling principles
of ensuring safe train operation, while the exact function
of a particular signalling system depends on the railway
track layout under its control.
We will give concrete examples from industrial practise in
the railway domain, showing how domain theories can help in
the formal verification process. The examples include
writing and validating formal specifications, formally
verifying implementations and analysing and communicating
the results of failed verifications.}
}
@TechReport{ it:2006-028,
author = {Ulrika Pettersson and Elisabeth Larsson and Gunnar
Marcusson and Jonas Persson},
title = {Improved Radial Basis Function Methods for
Multi-Dimensional Option Pricing},
institution = it,
department = tdb,
year = 2006,
number = {2006-028},
month = may,
abstract = {In this paper, we have derived a radial basis function
(RBF) based method for the pricing of financial contracts
by solving the Black-Scholes partial differential equation.
As an example of a financial contract that can be priced
with this method we have chosen the multi-dimensional
European basket call option. We have shown numerically that
our scheme is second order accurate in time and spectrally
accurate in space for constant shape parameter. For other,
non-optimal choices of shape parameter values, the
resulting convergence rate is algebraic. We propose an
adaptive node point placement that improves the accuracy
compared with a uniform distribution. Compared with an
adaptive finite difference method, the RBF method is 20-40
times faster in one and two space dimensions and has
approximately the same memory requirements.}
}
@TechReport{ it:2006-027,
author = {Jan Nordstr{\"o}m},
title = {Error Bounded Schemes for Time-Dependent Hyperbolic
Problems},
institution = it,
department = tdb,
year = 2006,
number = {2006-027},
month = may,
abstract = {In this paper we address the error growth in time for
hyperbolic problems on first order form. The energy method
is used to study when an error growth or a fixed error
bound is obtained. It is shown that the choice of boundary
procedure is a crucial point. Numerical experiments
corroborate the theoretical findings.}
}
@TechReport{ it:2006-026,
author = {Jan Nordstr{\"o}m and Ken Mattsson and Charles Swanson},
title = {Boundary Conditions for a Divergence Free
Velocity-Pressure Formulation of the Incompressible
{N}avier-{S}tokes Equations},
institution = it,
department = tdb,
year = 2006,
number = {2006-026},
month = may,
abstract = {New sets of boundary conditions for the velocity-pressure
formulation of the incompressible Navier-Stokes equations
are derived. The boundary conditions have the same form on
both inflow and outflow boundaries and lead to a divergence
free solution. Moreover, the specific form of the boundary
conditions makes it possible derive a symmetric positive
definite equation system for the internal pressure.
Numerical experiments support the theoretical conclusions.
}
}
@TechReport{ it:2006-025,
author = {Johan Wikstr{\"o}m and Arvid Kauppi and Arne W. Andersson
and Bengt Sandblad},
title = {Designing a Graphical User Interface for Train Traffic
Control},
institution = it,
department = hci,
year = 2006,
number = {2006-025},
abstract = {In 1996, on initiative of the Swedish National Rail
Administration, a research study was initiated by the
department of Human Computer Interaction at Uppsala
University with the aim to learn more about the problems
and difficulties involved in train traffic control. As a
result of this study, and the developing situation with
higher speeds, more frequent traffic, and many competing
train traffic operators, a research project was initiated.
The purpose was to find new strategies and technical
solutions for future train traffic control.
Modern research on human-computer interaction in complex
and dynamic systems provided a framework for how to design
an interface meeting these demands. Important aspects
concern e.g. workload, situation awareness and automated
cognitive processes, limitations in human memory capacity,
cognitive work environment problems, human error
performance and dynamic decision processes. Throughout the
research a user centered approach has been applied. The new
proposed interface is designed to integrate all decision
relevant information into one unified interface and to
support a continuous awareness of the dynamic development
of the traffic process. A prototype of new train traffic
control interface has been implemented in close
collaboration with active train dispatchers. Early and
promising in-house tests have been made using the prototype
described in this paper. More extensive case studies and
experiments need to be conducted before a complete
evaluation can be made.}
}
@TechReport{ it:2006-024,
author = {Arvid Kauppi and Johan Wikstr{\"o}m and Bengt Sandblad and
Arne W. Andersson},
title = {Control Strategies for Managing Train Traffic,
Difficulties Today and Solutions for the Future},
institution = it,
department = hci,
year = 2006,
number = {2006-024},
month = may,
abstract = {In 1996, on initiative from the Swedish National Rail
Administration, the department of Human-Computer
Interaction at the institute for Information Technology,
Uppsala University initiated a research project with the
objective to identify the difficulties present in today's
train traffic control today and to find solutions to those
problems, if possible.
This paper describes the strategy used to control train
traffic in Sweden today. Problems and difficulties
inherited from the use of the current control strategies
and systems are presented. With the goal to solve these
problems, and aid the human operator in their work,
solutions for new principles for control and a new control
strategy are proposed - control by re-planning. The
proposed control strategy is designed to support the train
dispatcher to work in a more preventive manner and thereby
avoiding potential disturbances in traffic when possible.
The focus of control tasks will be shifted from controlling
infrastructure on a technical level to focus more on a
higher level of controlling the traffic flow through
re-planning tasks. The new control strategy in combination
with a new approach to automation, higher availability of
decision relevant information and new graphical user
interfaces addresses many of the issues and problems found
in the control environment today.}
}
@TechReport{ it:2006-023,
author = {Gergana Bencheva and Svetozar Margenov and Ji\v{r}\'{\i}
Star\'{y}},
title = {{MPI} Implementation of a {PCG} Solver for Nonconforming
{FEM} Problems: Overlapping of Communications and
Computations},
institution = it,
year = 2006,
number = {2006-023},
month = may,
abstract = {New theoretical and experimental results concerning a
recently introduced parallel preconditioner for the
solution of large nonconforming Finite Element linear
systems are presented. The studied algorithm is based on
the modified incomplete Cholesky factorization MIC(0)
applied to a locally constructed approximation of the
original stiffness matrix. The overlapping of
communications and computations is possible due to a
suitable reordering of the computations applied in the MPI
code. Theoretical estimates for the execution time of the
modified algorithm are derived. The obtained improvement of
the real performance is illustrated by numerical tests on a
Beowulf-type Linux cluster, on a Sun symmetric
multiprocessor and on an SGI Altix supercluster.}
}
@TechReport{ it:2006-022,
author = {Niclas Sandgren and Petre Stoica},
title = {On Moving Average Parameter Estimation},
institution = it,
department = syscon,
year = 2006,
number = {2006-022},
month = apr,
abstract = {Estimation of the autoregressive moving average (ARMA)
parameters of a stationary stochastic process is a problem
often encountered in the signal processing literature. It
is well known that estimating the moving average (MA)
parameters is usually more difficult than estimating the
autoregressive (AR) part, especially if the zeros are
located close to the unit circle. In this paper we present
four linear methods for MA parameter estimation (i.e.,
methods that involve only linear operations) and compare
their performances first in a case when the zeros are
located far away from the unit circle and secondly in a
presumably harder case when the zeros are located very
close to the unit circle.}
}
@TechReport{ it:2006-021,
author = {Gunilla Linde and Jonas Persson and von Sydow, Lina},
title = {High-Order Adaptive Space-Discretizations for the
{B}lack--{S}choles Equation},
institution = it,
department = tdb,
year = 2006,
number = {2006-021},
month = apr,
abstract = {In this paper we develop a high-order adaptive finite
difference space-discretization for the Black--Scholes
(B--S) equation. The final condition is discontinuous in
the first derivative yielding that the effective rate of
convergence is two, both for low-order and high-order
standard finite difference (FD) schemes. To obtain a
sixth-order scheme we use an extra grid in a limited space-
and time-domain. The new sixth-order method is called
FD6G2. The FD6G2-method is combined with space- and
time-adaptivity to further enhance the method. To obtain
solutions of high accuracy in several dimensions the
adaptive FD6G2-method is superior to both standard and
adaptive second-order FD-methods.}
}
@TechReport{ it:2006-020,
author = {Nicolas Beldiceanu and Pierre Flener and Xavier Lorca},
title = {Combining Tree Partitioning, Precedence, Incomparability,
and Degree Constraints, with an Application to Phylogenetic
and Ordered-Path Problems},
institution = it,
department = csd,
year = 2006,
number = {2006-020},
month = apr,
abstract = {The \emph{tree} and \emph{path} constraints, for digraph
partitioning by vertex disjoint trees and paths
respectively, are unified within a single global
constraint, including a uniform treatment of a variety of
useful side constraints, such as precedence,
incomparability, and degree constraints. The approach
provides a sharp improvement over an existing \emph{path}
constraint, but can also efficiently handle tree problems,
such as the phylogenetic supertree construction problem.
The key point of the filtering is to take partially into
account the strong interactions between the tree
partitioning problem and all the side constraints.}
}
@TechReport{ it:2006-019,
author = {Jing Gong and Jan Nordstr{\"o}m},
title = {Stable, Accurate and Efficient Interface Procedures for
Viscous Problems},
institution = it,
department = tdb,
year = 2006,
number = {2006-019},
month = apr,
abstract = {In this paper we investigate and study several different
interface procedures for finite difference methods applied
to viscous problems. The analysis show that stable,
accurate and efficient interface procedures can be
obtained. The analysis also show that only minor
differences of the various methods exist.}
}
@TechReport{ it:2006-018,
author = {Dan Wallin and Henrik L{\"o}f and Erik Hagersten and
Sverker Holmgren},
title = {Multigrid and Gauss-Seidel Smoothers Revisited:
Parallelization on Chip Multiprocessors},
institution = it,
year = 2006,
number = {2006-018},
month = apr,
abstract = {Efficient solutions of partial differential equations
require a match between the algorithm and the underlying
architecture. The new chip-multiprocessors, CMPs (a.k.a.
multicore), feature low intra-chip communication cost and
smaller per-thread caches compared to previous systems.
From an algorithmic point of view this means that data
locality issues become more important than communication
overheads. This may require re-evaluation of many existing
algorithms.
We have investigated parallel implementations of multigrid
methods using a temporally blocked, naturally ordered,
smoother implementation. Compared with the standard
multigrid solution based on the two-color red-black
algorithm, we improve the data locality often as much as
ten times, while our use of a fine-grained locking scheme
keeps the parallel efficiency high.
While our algorithm initially was inspired by CMPs, it was
surprising to see our OpenMP multigrid implementation run
up to 40 percent faster than the standard red-black
algorithm on an 8-way SMP system. Studying the smoother
part of the algorithm in isolation often shows it
performing two iterations at the same time as a single
iteration with an ordinary red-black smoother. Running our
smoother on a 32-thread UltraSPARC T1 (Niagara) SMT/CMP and
a simulated 32-way CMP demonstrates the communication cost
of our algorithm to be low on such architectures.}
}
@TechReport{ it:2006-017,
author = {Andr{\'e} Yamba Yamba and Krister {\AA}hlander and Malin
Ljungberg},
title = {Designing for Geometrical Symmetry Exploitation},
institution = it,
department = tdb,
year = 2006,
number = {2006-017},
month = apr,
abstract = {Symmetry exploiting software based on the generalized
Fourier transform (GFT) is presented from a practical
design point of view. The algorithms and data structures
map closely to the relevant mathematical abstractions,
which primarily are based upon representation theory for
groups. Particular care has been taken in the design of the
data layout of the performance sensitive numerical data
structures.
The use of a vanilla strategy is advocated for the design
of flexible mathematical software libraries: An efficient
general-purpose routine should be supplied, to obtain a
practical and useful system, while the possibility to
extend the library and replace the default routine with a
special-purpose---even more optimized---routine should be
supported.
Compared with a direct approach, the performance results
show the superiority of the GFT based approach for
so-called dense equivariant systems. The application is
found to be well suited for parallelism.}
}
@TechReport{ it:2006-016,
author = {Johan Petrini and Tore Risch},
title = {Scalable {RDF} Views of Relational Databases through
Partial Evaluation},
institution = it,
department = csd,
year = 2006,
number = {2006-016},
month = mar,
note = {Updated April 2006},
abstract = {The semantic web represents meta-data as a triple relation
using the RDF data model. We have developed a system to
process queries to RDF views of entire relational
databases. Optimization of queries to such views is
challenging because i) RDF views of entire relational
databases become large unions, and ii) queries to the views
are more general than relational database queries, making
no clear distinction between data and schema. As queries
need not be expressed in terms of a schema, it becomes
critical to optimize not only data access time but also the
time to perform the query optimization itself. We have
developed novel query optimization techniques for scalable
queries to RDF views of relational databases. Our
optimization techniques are based on partial evaluation, a
method for compile time evaluation of subexpressions. We
show dramatic improvements in query optimization time when
scaling the query size while still producing high quality
execution plans. Our query optimization techniques enable
execution of real-world queries to RDF views of relational
databases.}
}
@TechReport{ it:2006-015,
author = {Jonas Persson and Jonatan Eriksson},
title = {Pricing Turbo Warrants},
institution = it,
department = tdb,
year = 2006,
number = {2006-015},
month = mar,
abstract = {We numerically price the financial contracts named turbo
warrant that were released early in 2005. They have been
studied mathematically in \cite{Eriksson05} where explicit
pricing formulas for the Geometric Brownian motion were
derived. For more general underlying stochastic processes
we have no analytical formulas and numerical methods are
necessary. In this work two different methods are compared,
stochastic pricing using a Monte Carlo method and a
deterministic PDE approach using finite differences. The
methods are evaluated in terms of numerical efficiency,
computation time and accuracy. In the numerical experiments
the geometric Brownian motion has been used as underlying
stochastic process. Our results show that for low accuracy
the methods are almost equal in efficiency but for higher
accuracy the finite difference method is much more
efficient.}
}
@TechReport{ it:2006-014,
author = {Amoignon, O.},
title = {Moving Mesh Adaptation for Aerodynamic Shape
Optimization},
institution = it,
department = tdb,
year = 2006,
number = {2006-014},
month = mar,
abstract = {A method of mesh adaptation is proposed for gradient-based
aerodynamic shape optimization. The method consists in
coupling an equation for the mesh node coordinates with the
discretized Euler equations of gas dynamics in steady
state. The variational mesh equation is inspired by
Winslow's variable diffusion mapping. The system of mesh
and flow equations is solved, instead of the flow equations
alone, when performing shape optimization. The solution
algorithm of the coupled equations is an approximate Newton
method supplemented with an interpolation of the variable
diffusivity by radial basis functions.
Tests are carried out for supersonic flow over a wedge, a
problem that is used here as a benchmark for the mesh
adaptation and for a simple problem of inverse design. At a
given design, the method of adaptation improves the
accuracy of the calculated drag, a functional that is used
in the construction of the inverse problem. The accuracy of
the shape, obtained by inverse design, experiences similar
improvements due to the mesh adaptation scheme.}
}
@TechReport{ it:2006-013,
author = {Amoignon, O. and Berggren, M.},
title = {Adjoint of a Median-Dual Finite-Volume Scheme Applied to
{2D} and {3D} Transonic Aerodynamic Shape Optimization},
institution = it,
department = tdb,
year = 2006,
number = {2006-013},
month = mar,
abstract = {The sensitivity analysis is a crucial step in algorithms
for gradient-based aerodynamic shape optimization. The
analysis involves computing the gradient of functionals
such as drag, lift, or aerodynamic moments, with respect to
the parameters of the design. Gradients are efficiently
calculated by solving adjoints of the linearized flow
equations. The flow is modeled by the Euler equations of
gas dynamics, solved in Edge, a Computational Fluid
Dynamics (CFD) code for unstructured meshes. The adjoint
equations and expressions for the gradients are derived
here in the fully discrete case, that is, the mappings from
the design variables to the functional's values involve the
discretized flow equations, a mesh deformation equation,
and the parameterization of the geometry. We present a
formalism and basic properties that enable a compact
derivation of the adjoint for discretized flow equations
obeying an edge-based structure, such as the
vertex-centered median-dual finite volume discretization
implemented in Edge. This approach is applied here to the
optimization of the RAE~2822 airfoil and the ONERA~M6 wing.
In particular, we show a method to parameterize the shape,
in 2D, in order to enforce smoothness and linear
geometrical constraints.}
}
@TechReport{ it:2006-012,
author = {Marianne Ahlford and Martin Andersson and Hanna Blomquist
and Magnus Ekstr{\"o}m and Lars Ericsson and Johannes
Gumbel and Anna Holmgren and Petter Holmberg and Leonard
Kia and Anton Lindstr{\"o}m and Magnus Lyrberg and Shaman
Mahmoudi and Bengt Nolin and Jesper Sundien and Henrik
Wallentin and Olle G{\"a}llmo and Anders Hessel and Leonid
Mokrushin and Paul Pettersson},
title = {Uppsala {U}nderdogs - A Robot Soccer Project},
institution = it,
department = docs,
year = 2006,
number = {2006-012},
month = mar,
abstract = {In this paper, we describe the four-legged soccer team
Uppsala Underdogs developed by a group of 4th year computer
science students at Uppsala University during the fall of
2004. The project is based on the experience from two
similar previous projects. This year the emphasis of the
project has been on distribution of data and on support for
evaluation and reconfiguration of strategies. To support
data distribution, a middleware has been developed, which
implements a replication algorithm and provides a clean
interface for the other software modules (or behaviors). To
enable easy reconfiguration of strategies, an
automata-based graphical description language has been
developed, which can be compiled into code that uses the
database and the lower level modules, such as tactics and
positioning, to make decisions and control the robot. In
addition, a graphical simulator has been developed in which
the strategies can be evaluated.}
}
@TechReport{ it:2006-011,
author = {Bahram Bahar and Adam Bolcsfoldi and Jonas Falkevik and
Roger Jakobsen and Kristoer Kobosko and Jimmy Kallstrom and
Alexander Harju and Andreas Hasselberg and Johan Persson
and Mattias Wadman and Olle G{\"a}llmo and Anders Hessel
and Leonid Mokrushin and Paul Pettersson.},
title = {Developing {A-GPS} as a Student Project},
institution = it,
department = docs,
year = 2006,
number = {2006-011},
month = mar,
abstract = {The project consists of ten fourth-year computer science
students at Uppsala University developing an A-GPS
(Assisted-GPS) system. During the fall term of 2005 the
students have developed a module for GPS-calculations in a
GSM-network and an application that demonstrates a possible
way of using the calculations module. This paper describes
the design, the development process and the results of the
project.}
}
@TechReport{ it:2006-010,
author = {Mattias Andreasson and Andr{\'e}e Bylund and Syrus Dargahi
and Daniel Johansson and Martin Larsson and Bennie Lundmark
and Jonas Mellberg and Fredrik Stenh and Olle G{\"a}llmo
and Anders Hessel and Leonid Mokrushin and Paul Pettersson},
title = {Project {A}vatar - Developing a Distributed Mobile Phone
Game},
institution = it,
department = docs,
year = 2006,
number = {2006-010},
month = mar,
note = {Online copy corrected April 7, 2006},
abstract = {Team Avatar, as the members of Project Avatar have come to
be known by, is a group of 4th year computer science
students at Uppsala University that have been developing a
distributed mobile phone game during the fall of 2005. In
this paper we describe the general design and environment
of the result of Project Avatar -- the game Three Crowns.}
}
@TechReport{ it:2006-009,
author = {Parosh Aziz Abdulla and Noomene Ben Henda and Richard Mayr
and Sven Sandberg},
title = {Eager Markov Chains},
institution = it,
department = docs,
year = 2006,
number = {2006-009},
month = mar,
abstract = {We consider infinite-state discrete Markov chains which
are \emph{eager}: the probability of avoiding a defined set
of final states for more than $n$ steps decreases
exponentially in $n$. We study the problem of computing the
expected reward (or cost) of runs until reaching the final
states, where rewards are assigned to individual runs by
computable reward functions. We present a path exploration
scheme, based on forward reachability analysis, to
approximate the expected reward up-to an arbitrarily small
error, and show that the scheme is guaranteed to terminate
in the case of eager Markov chains. We show that eager
Markov chains include those induced by Probabilistic Vector
Addition Systems with States, Noisy Turing Machines, and
Probabilistic Lossy Channel Systems.}
}
@TechReport{ it:2006-008,
author = {Pavel Krcal and Wang Yi},
title = {Communicating Timed Automata: The More Synchronous, the
More Difficult to Verify},
institution = it,
department = docs,
year = 2006,
number = {2006-008},
month = mar,
abstract = {We study channel systems whose behaviour (sending and
receiving messages via unbounded FIFO channels) must follow
given timing constraints specifying the execution speeds of
the local components. We propose Communicating Timed
Automata (CTA) to model such systems. The goal is to study
the borderline between decidable and undecidable classes of
channel systems in the timed setting. Our technical results
include: (1) CTA with one channel without shared states in
the form $(A_1,A_2, c_{1,2})$ is equivalent to one-counter
machine, implying that verification problems such as
checking state reachability and channel boundedness are
decidable, and (2) CTA with two channels without sharing
states in the form $(A_1,A_2,A_3, c_{1,2},c_{2,3})$ has the
power of Turing machines. Note that in the untimed setting,
these systems are no more expressive than finite state
machines. We show that the capability of synchronizing on
time makes it substantially more difficult to verify
channel systems.}
}
@TechReport{ it:2006-007,
author = {Stefan Engblom},
title = {Gaussian Quadratures with Respect to Discrete Measures},
institution = it,
department = tdb,
year = 2006,
number = {2006-007},
month = feb,
abstract = {In analogy to the subject of Gaussian integration formulas
we present an overview of some Gaussian \emph{summation}
formulas. The derivation involve polynomials that are
orthogonal under discrete inner products and the resulting
formulas are useful as a numerical device for summing
fairly general series. Several illuminating examples are
provided in order to present various aspects of this not
very well-known technique.}
}
@TechReport{ it:2006-006,
author = {Hans Hansson (editor)},
title = {ARTES - A Network for Real-Time Research and Graduate
Education in Sweden 1997--2006},
institution = it,
department = docs,
year = 2006,
number = {2006-006},
note = {Also published as report MDH-MRTC-197/2006-1-SE,
M{\"a}lardalens H{\"o}gskola.},
abstract = {This book summarizes the results of the Swedish national
real-time systems research initiative ARTES and provides a
few representative examples of the science and scientific
results that have emerged from ARTES.
ARTES was supported by the Swedish Foundation for Strategic
Research (SSF), with a total of 95 MSEK between 1998 and
2006. ARTES has unified and given strength to the Swedish
real-time and embedded systems research community, and
contributed substantially to advancing Sweden's
international position in this area. ARTES has had a
catalytic and coordinating effect for a total research
effort extending far beyond the funding provided by SSF. It
has created important synergies between disciplines,
ensured industrial relevance in research, and facilitated
important academic and industrial networking for
approximately 100 senior researchers and some 200
post-graduate students.}
}
@TechReport{ it:2006-005,
author = {Magnus {\AA}gren and Pierre Flener and Justin Pearson},
title = {Inferring Variable Conflicts for Local Search from
High-Level Models},
institution = it,
department = csd,
year = 2006,
number = {2006-005},
month = feb,
note = {Updated March 2006},
abstract = {For efficiency reasons, neighbourhoods in local search
algorithms are often shrunk by only considering moves
modifying variables that actually contribute to the overall
penalty. These are known as conflicting variables. This is
a well-known technique for speeding up search.
State-of-the-art solutions to, e.g., the progressive party
problem exploit this with great success. We propose a way
of automatically and incrementally measuring the conflict
of a variable in a local search model and apply this to the
set variables of models expressed in existential
second-order logic extended with counting (ESOL+).
Furthermore, we show that this measure is lower-bounded by
an intuitive conflict measure, and upper-bounded by the
penalty of the model. We also demonstrate the usefulness of
the approach by replacing a built-in global constraint by a
modelled ESOL+ version thereof, while still obtaining
competitive results. This is especially attractive when a
particular (global) constraint is not built in.}
}
@TechReport{ it:2006-004,
author = {Owe Axelsson and Janos Karatson},
title = {Symmetric Part Preconditioning of the {CG} for {S}tokes
Type Saddle-Point Systems},
institution = it,
department = tdb,
year = 2006,
number = {2006-004},
month = feb,
abstract = {A nonsymmetric formulation of saddle-point systems is
considered and symmetric part preconditioning of the
conjugate gradient method (CGM) is applied. Linear and
superlinear convergence estimates are derived for the
finite element solution of the Stokes problem and of
Navier's equations of elasticity.}
}
@TechReport{ it:2006-003,
author = {Fredrik Bergholm},
title = {Intermittent Open Boundaries for Shallow Water Equations},
institution = it,
department = tdb,
year = 2006,
number = {2006-003},
month = feb,
abstract = {Shallow water equations are used in oceanography,
acoustics and electromagnetics. This report (to be
submitted as article) focuses on quickly moving shallow
water waves in oceanography (also Coriolis force). In wave
propagation modelling, it is very often attractive to split
up a numerical model into smaller pieces. For barotropic
wave modelling, in oceanography, this is almost a
necessity. Wave propagation in a submodel communicates with
adjacent region(s) by open boundaries. An open boundary is
always a half measure, but there are interesting ways of
making the open boundaries ``softer'' -- a kind of
half-open boundaries. In this article, we investigate the
usefulness of having \emph{intermittent open boundaries}.
They tend to produce less errors, and may be analyzed
analytically, also. The basic principle is to have both an
open boundary condition and a suitable so--called
transition condition.}
}
@TechReport{ it:2006-002,
author = {Torsten S{\"o}derstr{\"o}m},
title = {Statistical Analysis of the {F}risch Scheme for
Identifying Errors-in-Variables Systems},
institution = it,
year = 2006,
number = {2006-002},
month = jan,
abstract = {Several estimation methods have been proposed for
identifying errors-in-variables systems, where both input
and output measurements are corrupted by noise. One of the
promising approaches is the so called Frisch scheme. This
paper provides an accuracy analysis of the Frisch scheme
applied to system identification. The estimates of the
system parameters and the noise variances are shown to be
asymptotically Gaussian distributed. An explicit expression
for the covariance matrix of the asymptotic distribution is
given as well. Numerical simulations support the
theoretical results. A comparison with the Cramer-Rao lower
bound is also given in examples, and it is shown that the
Frisch scheme gives a performance close to the Cramer-Rao
bound for large signal-to-noise ratios. }
}
@TechReport{ it:2006-001,
author = {Lars Ferm and Per L{\"o}tstedt},
title = {Numerical Method for Coupling the Macro and Meso Scales in
Stochastic Chemical Kinetics},
institution = it,
department = tdb,
year = 2006,
number = {2006-001},
month = jan,
abstract = {A numerical method is developed for simulation of
stochastic chemical reactions. The system is modeled by the
Fokker-Planck equation for the probability density of the
molecular state. The dimension of the domain of the
equation is reduced by assuming that most of the molecular
species have a normal distribution with a small variance.
The numerical approximation preserves properties of the
analytical solution such as non-negativity and constant
total probability. The method is applied to a nine
dimensional problem modelling an oscillating molecular
clock. The oscillations stop at a fixed point with a
macroscopic model but they continue with our two
dimensional, mixed macroscopic and mesoscopic model.}
}
@TechReport{ it:2005-044,
author = {Paul Sj{\"o}berg and Per L{\"o}tstedt and Johan Elf},
title = {{F}okker-{P}lanck Approximation of the Master Equation in
Molecular Biology},
institution = it,
department = tdb,
year = 2005,
number = {2005-044},
month = dec,
abstract = {The master equation of chemical reactions is solved by
first approximating it by the Fokker-Planck equation. Then
this equation is discretized in the state space and time by
a finite volume method. The difference between the solution
of the master equation and the discretized Fokker-Planck
equation is analyzed. The solution of the Fokker-Planck
equation is compared to the solution of the master equation
obtained with Gillespie's Stochastic Simulation Algorithm
(SSA) for problems of interest in the regulation of cell
processes. The time dependent and steady state solutions
are computed and for equal accuracy in the solutions, the
Fokker-Planck approach is more efficient than SSA for low
dimensional problems and high accuracy. }
}
@TechReport{ it:2005-043,
author = {Krister {\AA}hlander},
title = {Sparse Generalized {F}ourier Transforms},
institution = it,
department = tdb,
year = 2005,
number = {2005-043},
month = dec,
abstract = {Block-diagonalization of sparse equivariant discretization
matrices is studied. Such matrices typically arise when
partial differential equations that evolve in symmetric
geometries are discretized via the finite element method or
via finite differences.
By considering sparse equivariant matrices as equivariant
graphs, we identify a condition for when
block-diagonalization via a sparse variant of a generalized
Fourier transform (GFT) becomes particularly simple and
fast.
Characterizations for finite element triangulations of a
symmetric domain are given, and formulas for assembling the
block-diagonalized matrix directly are presented. It is
emphasized that the GFT preserves symmetric (Hermitian)
properties of an equivariant matrix.
By simulating the heat equation at the surface of a sphere
discretized by an icosahedral grid, it is demonstrated that
the block-diagonalization pays off. The gain is significant
for a direct method, and modest for an iterative method.
A comparison with a block-diagonalization approach based
upon the continuous formulation is made. It is argued that
the sparse GFT method is an appropriate way to discretize
the resulting continuous subsystems, since the spectrum and
the symmetry are preserved.}
}
@TechReport{ it:2005-042,
author = {Olof Sivertsson},
title = {Construction of Synthetic {CDO} Squared},
institution = it,
department = csd,
year = 2005,
number = {2005-042},
month = dec,
note = {M.Sc. thesis},
abstract = {We present techniques used in the implementation of an
efficient constraint program for the portfolio optimization
(PO) problem. This important combinatorial problem in the
credit derivatives market arises for example when
constructing synthetic collateralized debt obligations
(CDOs) squared. A close relationship with the balanced
incomplete block design (BIBD) problem exists which we make
use of. Due to the large size of typical PO instances,
global solving is not possible, instead we embed and solve
sub-instances. The high quality of our approximate
solutions can be assessed by comparison with a tight lower
bound on the cost. Together with detection of BIBDs,
symmetry breaking, extended reuse of already solved
instances, and existence-checking during search, the
performance of the program becomes good enough for
constructing optimal portfolios of CDOs squared, with sizes
common in the credit derivatives market, within minutes or
seconds.}
}
@TechReport{ it:2005-041,
author = {H{\aa}kan Zeffer and Zoran Radovic and Martin Karlsson and
Erik Hagersten},
title = {{TMA}: A Trap-Based Memory Architecture},
institution = it,
department = docs,
year = 2005,
number = {2005-041},
month = dec,
note = {Revised version of Technical Report 2005-015},
abstract = {The advances in semiconductor technology have set the
shared-memory server trend towards processors with multiple
cores per die and multiple threads per core. We believe
that this technology shift forces a reevaluation of how to
interconnect multiple such chips to form larger systems.
This paper argues that by adding support for
\textit{coherence traps} in future chip multiprocessors,
large-scale server systems can be formed at a much lower
cost. This is due to shorter design time, verification and
time to market when compared to its traditional
all-hardware counter part. In the proposed
\textit{trap-based memory architecture} (TMA), software
trap handlers are responsible for obtaining read/write
permission, whereas the coherence trap hardware is
responsible for the actual permission check.
In this paper we evaluate a TMA implementation (called
\textit{TMA Lite}) with a minimal amount of hardware
extensions, all contained within the processor. The
proposed mechanisms for coherence trap processing should
not affect the critical path and have a negligible cost in
terms of area and power for most processor designs.
Our evaluation is based on detailed full system simulation
using out-of-order processors with one or two dual-threaded
cores per die as processing nodes. The results show that a
TMA based distributed shared memory system can on average
perform within 1 percent of a highly optimized hardware
based design.}
}
@TechReport{ it:2005-040,
author = {Martin Karlsson},
title = {Conserving Memory Bandwidth in Chip Multi-Processors with
Runahead Execution},
institution = it,
department = docs,
year = 2005,
number = {2005-040},
month = dec,
abstract = {The introduction of chip multiprocessors (CMPs) presents
new challenges and trade-offs to computer architects.
Architects must now strike a balance between the number of
cores per chip versus the amount of on-chip cache and
available pin bandwidth. Technology projections predict
that the cost of pin bandwidth will increase significantly
and may therefore limit the number of processor cores per
CMP.
We observe a trend in many processor designs towards larger
cache blocks for the highest level on-chip cache. A large
cache block size is beneficial for workloads with a high
amount of spatial locality. Our study confirms previous
observations finding that significant parts of medium-sized
cache blocks that are brought on-chip often remain unused
and therefore wastefully consume pin bandwidth, especially
for the commercial workloads studied. In this paper we
target this waste by proposing a method of fine-grained
fetches.
In this paper we show that due to characteristics of
runahead execution it is possible to remove the implicit
assumption that programs exhibit abundant spatial locality,
with a limited performance impact. We demonstrate, using
execution-driven full system simulation, that our method of
fine-grained fetching can obtain significant performance
speedups in bandwidth constrained systems but also yield
stable performance systems that are not bandwidth limited.
}
}
@TechReport{ it:2005-039,
author = {Erik Nordstr{\"o}m and Richard Gold and Per Gunningberg},
title = {Mythbusters: Whatever You Thought About {MANET} Routing,
Think Again...},
institution = it,
department = docs,
year = 2005,
number = {2005-039},
month = nov,
abstract = {Protocol and system designs suffer from myths that may
affect their nature and purpose as well as their features
and capabilities. We investigate the myths surrounding
mobile ad hoc networks (MANETs) and the impact of these
myths on the ability to build robust, efficient and simple
routing protocols. We find that myths arise because of
complexity and ambiguous design and lead to confusing
protocol specifications, making the protocols difficult to
understand and implement in running systems. For example,
both AODV and DSR are confused about their nature as
routing protocols and both blur the distinction between
routing and forwarding. Building on experiences from
implementing AODV and DSR, we dissect these protocols and
try to dispel the myths surrounding them. From this
dissection, we describe a new routing protocol called
Partial Link State routing (PLS). PLS is a synthesis of
routing concepts from AODV and DSR with a clearer design
description and decoupling of routing and forwarding.}
}
@TechReport{ it:2005-038,
author = {GianLuigi Ferrari and Ugo Montanari and Emilio Tuosto and
Bj{\"o}rn Victor and Kidane Yemane},
title = {Modelling Fusion Calculus using HD-Automata},
institution = it,
year = 2005,
number = {2005-038},
month = nov,
note = {A shorter version appeared in the proceedings of CALCO
2005},
abstract = {We propose a coalgebraic model of the Fusion calculus
based on HD-automata. The main advantage of the approach is
that the partition refinement algorithm designed for
HD-automata is easily adapted to handle Fusion calculus
processes. Hence, the transition systems of Fusion calculus
processes can be minimised according to the notion of
observational semantics of the calculus. As a beneficial
side effect, this also provides a bisimulation checker for
Fusion calculus. }
}
@TechReport{ it:2005-037,
author = {Marino Miculan and Emilio Tuosto and Kidane Yemane},
title = {{HD}-Automata for Open Bisimulation},
institution = it,
department = docs,
year = 2005,
number = {2005-037},
month = nov,
abstract = {HD-automata are a syntax-independent operational model
introduced for dealing with history-dependent formalisms.
This kind of enriched automata, where states, transitions,
and labels are equipped with \emph{names} and
\emph{symmetries}, have been successfully applied for
modelling early and late bisimulation in $\pi$-calculus and
hyperbisimulation in Fusion calculus. However, current
HD-automata are not adequate for modelling open
bisimulation, because in HD-automata two names cannot be
unified, while open bisimulation is closed under all
possible name substitution respecting name distinctions. In
this paper we tackle the problem by integrating in the
definition of \emph{named sets}, the basic building blocks
of HD-automata, a notion of \emph{distinction:} names can
coalesce if the distinction allows to. Then, we use
HD-automata over named sets with distinctions for modelling
the open bisimulation of $\pi$-calculus. Finally, we
discuss the relationship between named sets with
distinctions and their HD-automata, with the categorical
counterparts based on presheaf categories.}
}
@TechReport{ it:2005-036,
author = {Mahen Jayawardena and Kajsa Ljungberg and Sverker
Holmgren},
title = {Using Parallel Computing and Grid Systems for Genetic
Mapping of Multifactorial Traits},
institution = it,
department = tdb,
year = 2005,
number = {2005-036},
month = dec,
abstract = {We present a flexible parallel implementation of the
exhaustive grid search algorithm for multidimensional QTL
mapping problems. A generic, parallel algorithm is
presented and a two-level scheme is introduced for
partitioning the work corresponding to the independent
computational tasks in the algorithm. At the outer level, a
static block-cyclic partitioning is used, and at the inner
level a dynamic pool-of-tasks model is used. The
implementation of the parallelism at the outer level is
performed using scripts, while MPI is used at the inner
level. By comparing to results from the SweGrid system to
those obtained using a shared memory server, we show that
this type of application is highly suitable for execution
in a grid framework.}
}
@TechReport{ it:2005-035,
author = {Kajsa Ljungberg and Kateryna Mishchenko and Sverker
Holmgren},
title = {Efficient Algorithms for Multi-Dimensional Global
Optimization in Genetic Mapping of Complex Traits},
institution = it,
department = tdb,
year = 2005,
number = {2005-035},
month = nov,
abstract = {We present a two-phase strategy for optimizing a
multi-dimensional, non-convex function arising during
genetic mapping of quantitative traits. Such traits are
believed to be affected by multiple so called QTL, and
searching for d QTL results in a d-dimensional optimization
problem with a large number of local optima. We combine the
global algorithm DIRECT of Jones et al. with a number of
local optimization methods that accelerate the final
convergence, and adapt the algorithms to problem-specific
features. We also improve the evaluation of the QTL mapping
objective function to enable exploitation of the smoothness
properties of the optimization landscape. Our best
two-phase method is demonstrated to be accurate in at least
six dimensions and up to ten times faster than currently
used QTL mapping algorithms.}
}
@TechReport{ it:2005-034,
author = {Maria Eriksson},
title = {Detecting Symmetries in Relational Models of {CSP}s},
institution = it,
department = csd,
year = 2005,
number = {2005-034},
month = nov,
note = {M.Sc. thesis},
abstract = {This master's thesis studies symmetry detection in
constraint satisfaction problems (CSPs). After modelling
some well-known CSPs in a relational language, the
symmetries of the single constraints in the models are
studied. These results are then transformed into general
patterns for symmetry detection. When the symmetries of the
single constraints have been detected, symmetries for
complete CSPs, with one or more constraints, are derived
compositionally. This work deals with value as well as
variable interchangeability.}
}
@TechReport{ it:2005-033,
author = {Kajsa Ljungberg},
title = {Efficient Evaluation of the Residual Sum of Squares for
Quantitative Trait Locus Models in the Case of Complete
Marker Genotype Information},
institution = it,
department = tdb,
year = 2005,
number = {2005-033},
month = nov,
abstract = {\textbf{Motivation:} A core computation of many popular
quantitative trait locus, QTL, mapping methods is
determining the residual sum of squares, RSS, for a
regression of trait values on (pseudo-)marker genotypes. A
single evaluation is easily performed using the standard
method QR factorization, but together the RSS computations
take considerable time and often constitute the major part
of the computational effort.
\textbf{Results:} We present an algorithm for RSS
evaluation that is mathematically equivalent to evaluation
via QR factorization but 10-100 times faster depending on
the model and data dimensions. It can be used for all
standard QTL models. Our method opens the possibility for
more detailed data analysis and more extensive model
comparisons.
\textbf{Availability:} C code, detailed derivations and
general implementation strategies are available from the
author on request.
\textbf{Contact:} kajsa.ljungberg@it.uu.se}
}
@TechReport{ it:2005-032,
author = {Johansson, Niklas and Sandblad, Bengt},
title = {Efficient {IT} support in care for the elderly -
Experiences from the {VIHO} project},
institution = it,
department = hci,
year = 2005,
number = {2005-032},
month = nov,
abstract = {The main research objective for the VIHO project
(Efficient Computer Support in Care for the Elderly) was to
investigate how a home care and help service organization
can be developed in order to be better prepared for future
challenges, and how new technical systems could support the
development process. We have studied the home help
personnels need for support and investigated how the new
organization could be formed in order to provide a healthy
and sustainable work. Initial focus has been on the
essential parts of the work and how the work could be
improved in the future, and not on design of the technical
support systems. Our basic point of view has been that
correctly used, new technology can contribute, so that work
and organisation develops in a positive way, patients are
feeling sequre and the personnels work environment is
improved. This means that the organisation better can
fulfil expectations and requirements. The professions can
be strengthened and the organisation will be able to meet
future challanges. In this report we briefly describe the
results and the methods used in the project.}
}
@TechReport{ it:2005-031,
author = {Jan Nordstr{\"o}m and R.C. Swanson},
title = {Boundary Conditions for a Divergence Free
Velocity-Pressure Formulation of the Incompressible
{N}avier-{S}tokes Equations},
institution = it,
department = tdb,
year = 2005,
number = {2005-031},
month = nov,
day = 9,
abstract = {New sets of boundary conditions for the velocity-pressure
formulation of the incompressible Navier-Stokes equations
are derived. The boundary conditions have the same form on
both inflow and outflow boundaries and lead to a divergence
free solution.}
}
@TechReport{ it:2005-030,
author = {Erik B{\"a}ngtsson},
title = {A Consistent Stabilized Formulation for a Nonsymmetric
Saddle-Point Problem},
institution = it,
department = tdb,
year = 2005,
number = {2005-030},
month = oct,
abstract = {In this report we study the stability of a nonsymmetric
saddle-point problem. It is discretized with equal order
finite elements and stabilized with a consistent
regularization. In this way we achieve a stable finite
element discretization of optimal order approximation
properties.}
}
@TechReport{ it:2005-029,
author = {Niklas Johansson and Stina Nylander},
title = {Usability in Mobile {IT} systems},
institution = it,
department = hci,
year = 2005,
number = {2005-029},
month = oct,
abstract = {In this report we give an overview of usability aspects
applicable to mobile devices and systems. A number of
research projects from three different application areas
are presented and experiences from the projects are
discussed. To successfully design usable products, services
and systems both for leisure and for mobile work practice
has turned out to be a difficult undertaking. Many systems
fail because of a number of reasons. Some systems do not
fail, but remains difficult and cumbersome to use. A
certain immaturity can be observed since developers and
designers do not fully utilise the benefits and assets
provided by today's technology in design of mobile systems.
For mobile systems, the varying contexts of use become more
important. When only relying on existing knowledge of
design for stationary systems, important possibilities are
often lost and the system has gone astray.}
}
@TechReport{ it:2005-028,
author = {Erik Berg and H{\aa}kan Zeffer and Erik Hagersten},
title = {A Statistical Multiprocessor Cache Model},
institution = it,
department = docs,
year = 2005,
number = {2005-028},
month = oct,
abstract = {The introduction of general purpose microprocessors
running multiple threads will put a focus on methods and
tools helping a programmer to write efficient parallel
applications. Such tool should be fast enough to meet a
software developer's need for short turn-around time, but
also accurate and flexible enough to provide trend-correct
and intuitive feedback.
This paper describes an efficient and flexible approach for
modeling the memory system of a multiprocessor, such as
those of chip multiprocessors (CMPs). Sparse data is
sampled during a multithreaded execution. The data
collected consist of the reuse distance and invalidation
distribution for a small subset of the memory accesses.
Based on the sampled data from a single run, a new
mathematical formula can be used to estimate the miss rate
for a memory hierarchy built from caches of arbitrarily
size, cacheline size and degree of sharing. The formula
further divides the misses into six categories to further
aid the software developer.
The method is evaluated using a large number of commercial
and technical multithreaded applications. The result
produced by our algorithm fed with sparse sampling data is
shown to be consistent with results gathered during
traditional architecture simulation.}
}
@TechReport{ it:2005-027,
author = {Timo Qvist},
title = {Fast Simulation of Concurrent Agents with P-Nets - the
GPSim tool},
institution = it,
department = docs,
year = 2005,
number = {2005-027},
month = sep,
note = {M.Sc. thesis},
abstract = {The aim of this thesis was to investigate and enlighten
the applicability of P-Nets for simulating large and
possibly infinite--control systems. P-Nets are generalized
coloured Petri nets \cite{Petri62} which retain detailed
information in the tokens regarding firing history and the
scope of concurrently executing threads. P-Nets are
specified with the help of a process calculi called CCS$_k$
which is a derivation of Milner's CCS \cite{milner89}, and
converted to a P-Net representation prior to simulation. A
simulation tool named GPSim was implemented using both
generic optimization techniques and techniques specific to
P-Net structure and semantics. The simulation performance
of GPSim was evaluated and compared to two well--known
formal verification tools with respectable pedigrees; Bell
Labs' Spin and The Concurrency Workbench of the New Century
from Stony Brook University.}
}
@TechReport{ it:2005-026,
author = {Erik Abenius and Fredrik Edelvik and Christer Johansson},
title = {Waveguide Truncation Using {UPML} in the Finite-Element
Time-Domain Method},
institution = it,
department = tdb,
year = 2005,
number = {2005-026},
month = sep,
abstract = {An important part of numerical waveguide modeling is the
termination of the waveguide using artificial boundaries.
In this paper we develop a perfectly matched layer (PML)
for waveguides in the finite-element time-domain method
(FETD). The PML is discretized by prism elements aligned
with the direction of propagation of the waveguide.
Assuming that the waveguide is discretized by tetrahedra
such a grid is easily generated from a cross-sectional
surface in the waveguide. The proposed method has the
advantage of being general with regard to the geometry and
material of the waveguide. Previous works on PML for FETD
have reported problems with late-time instability. While
still present in the current approach, our results indicate
that the instability is less severe for the prism element
PML compared to a tetrahedral PML. Moreover, it may be
controlled by increasing the number of grid points in the
absorbing layer. It should be noted that the instability
appears long after the energy has been attenuated and
therefore pose no problems in practical computations. The
performance of the suggested scheme is demonstrated for
several waveguide problems, including an inhomogeneous
case.}
}
@TechReport{ it:2005-025,
author = {Paul Pettersson and Wang Yi (eds.)},
title = {Pre-Proceedings of the 3rd International Conference on
Formal Modelling and Analysis of Timed Systems},
institution = it,
department = docs,
year = 2005,
number = {2005-025},
month = sep
}
@TechReport{ it:2005-024,
author = {Torsten S{\"o}derstr{\"o}m and Erik K. Larsson and Kaushik
Mahata and Magnus Mossberg},
title = {Approaches for Continuous-Time Modeling in
Errors-in-Variables Identification},
institution = it,
department = syscon,
year = 2005,
number = {2005-024},
month = sep,
abstract = {Continuous-time identification is applied to an
errors-in-variables setting. A continuous-time model is
fitted to data consisting of discrete-time noise corrupted
input and output measurements. The noise-free input is
modelled as a continuous-time ARMA process. It is described
how the Cram{\'e}r-Rao lower bound for the estimation
problem can be computed. Several parameter estimation
approaches for the problem are presented, and also
illustrated in a short numerical study. }
}
@TechReport{ it:2005-023,
author = {Per L{\"o}tstedt and Lars Ferm},
title = {Dimensional Reduction of the {F}okker-{P}lanck Equation
for Stochastic Chemical Reactions},
institution = it,
department = tdb,
year = 2005,
number = {2005-023},
month = aug,
abstract = {The Fokker-Planck equation models chemical reactions on a
mesoscale. The solution is a probability density function
for the copy number of the different molecules. The number
of dimensions of the problem can be large making numerical
simulation of the reactions computationally intractable.
The number of dimensions is reduced here by deriving
partial differential equations for the first moments of
some of the species and coupling them to a Fokker-Planck
equation for the remaining species. With more simplifying
assumptions, another system of equations is derived
consisting of integro-differential equations and a
Fokker-Planck equation. In this way, the simulation of the
chemical networks is possible without the exponential
growth in computatational work and memory of the original
equation and with better modelling accuracy than the
macroscopic reaction rate equations. Some terms in the
equations are small and are ignored. Conditions are given
for the influence of these terms to be small on the
equations and the solutions. The difference between
different models is illustrated in a numerical example.}
}
@TechReport{ it:2005-022,
author = {Torbj{\"o}rn Wigren},
title = {{MATLAB} Software for Recursive Identification and Scaling
Using a Structured Nonlinear Black-box Model -- Revision
2},
institution = it,
department = syscon,
year = 2005,
number = {2005-022},
month = aug,
note = {Revised version of nr 2005-002. The software package can
be downloaded from
\url{http://www.it.uu.se/research/publications/reports/2005-022/NRISoftwareRev2.zip}}
,
abstract = {This reports is intended as a users manual for a package
of MATLAB scripts and functions, developed for recursive
prediction error identification of nonlinear state space
systems and nonlinear static systems. The core of the
package is an implementation of an output error
identification and scaling algorithm. The algorithm is
based on a continuous time, structured black box state
space model of a nonlinear system. An RPEM algorithm for
recursive identification of nonlinear static systems, that
re-uses the parameterization of the nonlinear ODE model, is
added in the present revision of the software package. The
software can only be run off-line, i.e. no true real time
operation is possible. The algorithm is however implemented
so that true on-line operation can be obtained by
extraction of the main algorithmic loop. The user must then
provide the real time environment. The software package
contains scripts and functions that allow the user to
either input live measurements or to generate test data by
simulation. The scripts and functions for the setup and
execution of the identification algorithms are somewhat
more general than what is described in the references.
There is e.g. support for automatic re-initiation of the
algorithms using the parameters obtained at the end of a
previous identification run. This allows for multiple runs
through a set of data, something that is useful for data
sets that are too short to allow convergence. The
re-initiation step also allows the user to modify the
degrees of the polynomial model structure and to specify
terms that are to be excluded from the model. This makes it
possible to iteratively re-fine the estimated model using
multiple runs. The functionality for display of results
include scripts for plotting of data, parameters,
prediction errors, eigenvalues and the condition number of
the Hessian. The estimated model obtained at the end of a
run can be simulated and the model output plotted, alone or
together with the data used for identification. Model
validation is supported by two methods apart from the
display functionality. First, calculation of the RPEM loss
function can be performed, using parameters obtained at the
end of an identification run. Secondly, the accuracy as a
function of the output signal amplitude can be assessed.}
}
@TechReport{ it:2005-021,
author = {Mei Hong and Torsten S{\"o}derstr{\"o}m and Wei Xing Zheng},
title = {Accuracy Analysis of Bias-Eliminating Least Squares
Estimates for Identification of Errors-in-Variables
Systems},
institution = it,
department = syscon,
year = 2005,
number = {2005-021},
month = aug,
abstract = {The bias-eliminating least squares (BELS) method is one of
the consistent estimators for identifying dynamic
errors-in-variables systems. The attraction of the BELS
method lies in its good accuracy and its modest
computational cost. In this report, we investigate the
accuracy properties of the BELS estimates. It is shown that
the estimated system parameters and the estimated noise
variances are asymptotically Gaussian distributed. An
explicit expression for the normalized covariance matrix of
the estimated parameters is derived and supported by some
numerical examples.}
}
@TechReport{ it:2005-020,
author = {Stefan Engblom},
title = {Computing the Moments of High Dimensional Solutions of the
Master Equation},
institution = it,
department = tdb,
year = 2005,
number = {2005-020},
month = jun,
day = 30,
abstract = {Derived from the Markov character only, the master
equation of chemical reactions is an accurate stochastic
description of quite general systems in chemistry. Exact
solutions of this equation are rare and the most frequently
used approximative solution method is to write down the
corresponding set of \emph{reaction rate} equations. In
many cases this approximation is not valid, or only
partially so, as stochastic effects caused by the natural
noise present in the full description of the problem are
poorly captured. In this paper it is shown how a certain
set of higher order equations can be derived. It is shown
by theory and example that stochastic effects are better
captured using this technique while still maintaining the
computational advantages of the reaction rate approach.}
}
@TechReport{ it:2005-019,
author = {Torsten S{\"o}derstr{\"o}m},
title = {Computing the Covariance Matrix for {PEM} Estimates and
the {C}ramer-{R}ao Lower Bound for Linear State Space
Models},
institution = it,
department = syscon,
year = 2005,
number = {2005-019},
month = jun,
abstract = {The paper presents a complete and comprehensive algorithm
for computing the asymptotic accuracy of estimated state
space models. The parameterization is assumed to be give a
uniquely identifiable system, but is otherwise general. It
is assumed that the system matrices and the noise
characteristics are smooth functions of the unknown
parameters. Expressions for the asymptotic covariance
matrix of the parameter estimates are derived for some
variants of the prediction error method. As a special case
for Gaussian distributed data, the Cram{\'e}r-Rao bound and
the covariance matrix for maximum likelihood estimates are
obtained.}
}
@TechReport{ it:2005-018,
author = {Eva Olsson and Niklas Johansson and Jan Gulliksen and
Bengt Sandblad},
title = {A Participatory Process Supporting Design of Future Work},
institution = it,
department = hci,
year = 2005,
number = {2005-018},
month = may,
day = 30,
abstract = {This paper illustrates how a participatory design process
has developed as a result of empirical studies with
workers. The view on design as a process presented here
necessitates an explicit analysis of work where both
workers and designers participate. The analysis gives
workers a possibility to reflect on present and future work
practices and to evaluate effects in advance. Moreover, it
provides designers insights that facilitate design of
support systems that match work complexity. It has often
been argued that the full potential of a new IT-support
system is not reached, but that only old work procedures
are preserved. It is one of the purposes of our work
re-design process to support creative changes of different
nature. To ascertain that the complexity of work is
acknowledged and that work redesign is enabled in the
design process, we recommend that workers participate to a
much higher degree than present. During a number of
projects this process has successively developed. In this
paper, the process is described, together with a selection
of cases where it has been applied. Important experiences
are the need for extensive user participation in the design
process and the time and resources the process must be
given.}
}
@TechReport{ it:2005-017,
author = {Tobias Bandh},
title = {Evaluation of Authentication Algorithms for Small
Devices},
institution = it,
department = docs,
year = 2005,
number = {2005-017},
month = may,
abstract = {Todays small devices get more and more the possibility to
communicate. This makes it more and more important to think
about security problems. One part of secure communication
is the authentication of the communication partner. The
communication partners have to prove to each other that
they are who they pretend to be.
In this work we compared several authentication protocols
to evaluate their suitability for usage on small devices.
We chose four examples which cover the four main categories
of authentication protocols: password-, public-key,
secret-key, and zero-knowledge authentication. In a first
step we analyzed them regarding to the number of exchanged
messages and their computational complexity. In a second
step two of the protocols were implemented for a Nokia 6610
mobile phone with Java MIDlets as small Device. The
counterpart on the server side was realized using Java
Servlets. We measured the times the protocols needed to
accomplish their task. The results of those two steps were
compared.
We concluded that the number of exchanged messages and in
particular the communication latency had a more significant
influence on the results than the computational complexity
of the protocols.}
}
@TechReport{ it:2005-016,
author = {H{\aa}kan Zeffer and Erik Hagersten},
title = {Adaptive Coherence Batching for Trap-Based Memory
Architectures},
institution = it,
department = docs,
year = 2005,
number = {2005-016},
month = may,
abstract = {Both software-initiated and hardware-initiated prefetching
have been used to accelerate shared-memory server
performance. While software-initiated prefetching require
instruction set and compiler support, hardware prefetching
often require additional hardware structures or extra
memory state.
The \textit{coherence batching} scheme proposed in this
paper keeps the system completely binary transparent and
does not rely on any additional hardware. Hence, it can be
implemented without additional hardware in software
coherent systems and improve performance for already
optimized and compiled binaries.
We have evaluated our proposals on a \textit{trap-based
memory architecture} where fine-grained coherence
permission checks are done in hardware but the coherence
protocol is run in software on the requesting processor.
Functional full-system simulation shows that our
software-only coherence-batch scheme is able to reduce the
number of coherence misses with up to 60 percent compared
to a system without coherence batching. The average miss
reduction is 37 percent while the average bandwidth usage
is reduced.}
}
@TechReport{ it:2005-015,
author = {H{\aa}kan Zeffer and Zoran Radovic and Martin Karlsson and
Erik Hagersten},
title = {{TMA}: A Trap-Based Memory Architecture},
institution = it,
department = docs,
year = 2005,
number = {2005-015},
month = may,
note = {A revised version is available as Technical Report
2005-041},
abstract = {The advances in semiconductor technology have set the
shared-memory server trend towards multiple cores per die
and multiple threads per core. We believe that this
technology shift forces a reevaluation of how to
interconnect multiple such chips to form larger systems.
This paper argues that minimal processor support for
coherence traps implemented in future chip multiprocessors
will provide large-scale server systems at a much lower
cost in terms of engineer years, verification and time to
market when compared to its traditional all-hardware
counter part. In our proposal, software trap handlers are
responsible for getting read/write permission, whereas the
coherence trap hardware is responsible for the actual
permission check.
Detailed full-system simulation shows that a coherence-trap
enabled distributed shared memory system can be performance
competitive with its highly optimized hardware-only counter
part. The evaluated systems use high-end processors with
one or two dual-threaded cores per die as processing
nodes.}
}
@TechReport{ it:2005-014,
author = {Richard Gold and Mats Uddenfeldt},
title = {Daigan: Constructing Proxy Networks with {S}el{N}et},
institution = it,
department = docs,
year = 2005,
number = {2005-014},
month = apr,
abstract = {We present Daigan, a tool for constructing distributed
proxy networks using the SelNet indirection layer. Using
the indirection capabilities of SelNet, we can construct
on-demand chains of proxies for adapting content for mobile
devices. Daigan takes a specification of a device's
capabilities and from that identifies which proxies are
needed to meet these requirements. Based on this
specification Daigan sets up a chain of proxies and
transparently redirects an application's traffic to the
proxy chain. We demonstrate Daigan's abilities through a
scenario which performs the instantiation of a proxy chain
consisting of a proxy cache, an image transcoder/compressor
and a TCP header compression proxy. We describe this
scenario in detail and report on implementation progress.}
}
@TechReport{ it:2005-013,
author = {H{\aa}kan Zeffer and Zoran Radovic and Erik Hagersten},
title = {Flexibility Implies Performance},
institution = it,
department = docs,
year = 2005,
number = {2005-013},
month = apr,
abstract = {No single coherence strategy suits all applications well.
Many promising adaptive protocols and coherence predictors,
capable of dynamically modifying the coherence strategy,
have been suggested over the years.
While most dynamic detection schemes rely on plentiful of
dedicated hardware, the customization technique suggested
in this paper requires no extra hardware support for its
per-application coherence strategy. Instead, each
application is profiled using a low-overhead profiling
tool. The appropriate coherence flag setting, suggested by
the profiling, is specified when the application is
launched.
We have compared the performance of a hardware DSM (Sun
WildFire) to a software DSM built with identical
interconnect hardware and coherence strategy. With no
support for flexibility, the software DSM runs on average
45 percent slower than the hardware DSM on the 12 studied
applications, while the flexibility can get the software
DSM within 11 percent. Our all-software system outperforms
the hardware DSM on four applications.}
}
@TechReport{ it:2005-012,
author = {Milena Ivanova and Tore Risch},
title = {Customizable Parallel Execution of Scientific Stream
Queries},
institution = it,
department = csd,
year = 2005,
number = {2005-012},
month = apr,
abstract = {Scientific applications require processing high-volume
on-line streams of numerical data from instruments and
simulations. We present an extensible stream database
system that allows scalable and flexible continuous queries
on such streams. Application dependent streams and query
functions are defined through an Object-Relational model.
Distributed execution plans for continuous queries are
described as high-level data flow distribution templates.
Using a generic template we define two partitioning
strategies for scalable parallel execution of expensive
stream queries: window split and window distribute. Window
split provides operators for customized parallel execution
of query functions whose complexity depends on size of the
data units on which they are applied. It reduces the size
of stream data units using application dependent functions
as parameters. By contrast, window distribute provides
operators for customized distribution of entire data units
without reducing their size. We evaluated these strategies
for a typical high volume scientific stream application and
show that window split is favorable when computational
resources are limited, while window distribute is better
when there are sufficient resources.}
}
@TechReport{ it:2005-011,
author = {Per Carlsson and Arne Andersson},
title = {A Flexible Model for Tree-Structured Multi-Commodity
Markets},
institution = it,
department = csd,
year = 2005,
number = {2005-011},
month = apr,
note = {Extended version of conference paper accepted for IEEE
CEC2005, M{\"u}nchen, July 2005},
abstract = {In this paper we study tree-structured multi-commodity,
multi-unit markets. The concept is a way to handle
dependencies between commodities on the market in a
tractable way. The winner determination problem of a
general combinatorial market is well known to be NP-hard.
It has been shown that on single-unit single-sided
combinatorial auctions with tree-structured bundles the
problem can be computed in polynomial time. We show that it
is possible to extend this to multi-unit double-sided
markets. Further it is possible to handle the commodities
of a bundle not only as complements but as perfect
substitutes too. Under certain conditions the computation
time is still polynomial.}
}
@TechReport{ it:2005-010,
author = {P{\"a}r Samuelsson and Bj{\"o}rn Halvarsson and Bengt
Carlsson},
title = {Cost-Efficient Operation of a Denitrifying Activated
Sludge Process - An Initial Study},
institution = it,
department = syscon,
year = 2005,
number = {2005-010},
month = apr,
abstract = {In this paper, possible choices of optimal set-points and
cost minimizing control strategies for the denitrification
process in an activated sludge process are discussed. In
order to compare different criterion functions, simulations
utilizing the European COST benchmark are considered. By
means of operational maps the results are visualized. It is
found that there is a clear set-point area where the
process can be said to be efficiently controlled in an
economic sense. For most reasonable operating points this
optimal area corresponds to a nitrate concentration in the
anoxic compartment in the interval 1-3 mg(N)/l.
Furthermore, the location of this optimum does not seem to
be very sensitive to changes in the ASM1 parameters. With
an appropriate nitrate cost function, the legislatory
authorities can place this economic optimum in an area
where also the effluent regulations are met. It is also
discussed how this efficient control can be accomplished.}
}
@TechReport{ it:2005-009,
author = {Claes Olsson},
title = {Disturbance Observer-Based Automotive Engine Vibration
Isolation Dealing with Non-Linear Dynamics and Transient
Excitation},
institution = it,
department = syscon,
year = 2005,
number = {2005-009},
month = apr,
abstract = {Active automotive engine vibration isolation is considered
where both stationary and transient engine-induced
excitations as well as plant non-linearity are considered.
The adopted control strategy targets the dominating
spectral components of the excitation and achieves narrow
band vibration isolation using feedback of disturbance
states estimates. Time-varying gain-scheduled observer
design, including investigations of closed-loop
characteristics, is based on a linear parameter varying
(LPV) approximation of the considered non-linear engine and
subframe suspension system. To generate this
representation, an approach of dividing the non-linear
system into its linear and non-linear components where the
latter is represented using a parameter dependent
non-linear function is proposed. Parameter dependent
quadratic stability analysis has been made tractable using
an affine closed-loop system representation.
High vibration isolation performance is demonstrated using
co-simulations incorporating a detailed non-linear plant
model and measured engine excitations. This is also
achieved for engine operating conditions corresponding to
rapid car accelerations, whereas the system exhibits
non-linear characteristics and the fundamental frequency of
the harmonic disturbance undergoes rapid time variations.
Parameter dependent closed-loop quadratic stability is
being shown assuming plant linearity. Yet, in the
non-linear plant case, stability is guaranteed but only for
limited intervals of the parameters and their time
derivatives.}
}
@TechReport{ it:2005-008,
author = {Linda Brus},
title = {Nonlinear Identification of a Solar Heating System},
institution = it,
department = syscon,
year = 2005,
number = {2005-008},
month = mar,
abstract = {The use of solar heating systems is a way of exploiting
the clean and free energy from the sun. To optimize the
energy gain from such a system, where the main input, the
solar insolation, is an uncontrollable variable, good
models of the system dynamics are required. Identification
methods are often either highly specialized for the
application or require an extensive amount of data,
especially when the dynamics studied are nonlinear. This
paper shows that by application of a new recursive system
identification technique, a small scale solar heating
system can be modeled with very little data, without having
to tailor the model structure to the application.}
}
@TechReport{ it:2005-007,
author = {Linda Brus},
title = {Nonlinear Identification of an Anaerobic Digestion
Process},
institution = it,
department = syscon,
year = 2005,
number = {2005-007},
month = mar,
abstract = {Anaerobic digestion in bioreactors is an important
technology for environmental friendly treatment of organic
waste. To optimize and control such processes accurate
dynamic models of the process are needed. Unfortunately,
modeling of anaerobic digestion often results in high order
nonlinear models with many unknown parameters, a fact that
complicates controller design. This paper attempts to
circumvent this problem, by application of new recursive
system identification techniques, thereby radically
reducing the degree of the models and the number of
parameters. Experiments show that a second order nonlinear
model is sufficient for accurate modeling of the system.}
}
@TechReport{ it:2005-006,
author = {Agnes Runqvist and Magnus Mossberg and Torsten
S{\"o}derstr{\"o}m},
title = {On Optimal Sensor Locations for Nonparametric
Identification of Viscoelastic Materials},
institution = it,
department = syscon,
year = 2005,
number = {2005-006},
month = feb,
abstract = {The problem of optimal sensor locations in nonparametric
identification of viscoelastic materials is considered.
Different criteria of the covariance matrix, connected to
A- and D-optimal experiment design, are considered and
evaluated. The results of the paper can be used to design
experiments with improved accuracy of the estimates.}
}
@TechReport{ it:2005-005,
author = {Torsten S{\"o}derstr{\"o}m},
title = {Accuracy Analysis of the {F}risch Scheme for Identifying
Errors-in-Variables Systems},
institution = it,
department = syscon,
year = 2005,
number = {2005-005},
month = feb,
abstract = {Several estimation methods have been proposed for
identifying errors-in-variables systems, where both input
and output measurements are corrupted by noise. One of the
promising approaches is the so called Frisch scheme. This
paper provides an accuracy analysis of the Frisch scheme
applied to system identification. The estimates of the
system parameters and the noise variances are shown to be
asymptotically Gaussian distributed. An explicit expression
for the covariance matrix of the asymptotic distribution is
given as well. Numerical simulations support the
theoretical results. A comparison with the Cramer-Rao lower
bound is also given in examples, and it is shown that the
Frisch scheme gives a performance close to the Cramer-Rao
bound for large signal-to-noise ratios.}
}
@TechReport{ it:2005-004,
author = {Michael Baldamus and Joachim Parrow and Bj{\"o}rn Victor},
title = {A Fully Abstract Encoding of the $\pi$-Calculus with Data
Terms},
institution = it,
department = docs,
year = 2005,
number = {2005-004},
month = feb,
note = {Updated April 2005},
abstract = {The $\pi$-calculus with data terms ($\pi$T) extends the
pure $\pi$-calculus by data constructors and destructors
and allows data to be transmitted between agents. It has
long been known how to encode such data types in $\pi$, but
until now it has been open how to make the encoding
\emph{fully abstract}, meaning that two encodings (in
$\pi$) are semantically equivalent precisely when the
original $\pi$T agents are semantically equivalent. We
present a new type of encoding and prove it to be fully
abstract with respect to may-testing equivalence. To our
knowledge this is the first result of its kind, for any
calculus enriched with data terms. It has particular
importance when representing security properties since
attackers can be regarded as may-test observers. Full
abstraction proves that it does not matter whether such
observers are formulated in $\pi$ or $\pi$T, both are
equally expressive in this respect. The technical new idea
consists of encoding data as table entries rather than
active processes, and using a firewalled central integrity
manager to ensure data security.}
}
@TechReport{ it:2005-003,
author = {Claes Olsson},
title = {Structure Flexibility Impacts on Robust Active Vibration
Isolation Using Mixed Sensitivity Optimisation},
institution = it,
department = syscon,
year = 2005,
number = {2005-003},
month = feb,
abstract = {Active vibration isolation from an arbitrarily,
structurally complex receiver is considered with respect to
the impacts of structure flexibility on the open- and
closed-loop system characteristics. Specifically, the
generally weak influence of flexibility on the open-loop
transfer function in case of total force feedback, in
contrast to acceleration feedback, is investigated.
The open-loop system characteristics are analysed based on
open-loop transfer function expressions obtained using
modal expansion and on modal model order reduction
techniques. To closely demonstrate and illustrate the
impacts of flexibility on the closed-loop system
performance and stability, a problem of automotive engine
vibration isolation from a flexible subframe is presented
where the neglected dynamics are represented as an output
multiplicative model perturbation.
A physical explanation to why the contribution of
flexibility to the open-loop transfer function could be
neglected in the case of total force feedback in contrast
to acceleration feedback is given. Factors for an
individual eigenmode to not significantly contribute to the
total force output are presented where the deviation of the
mode direction relative to the actuator force direction is
pointed out as a key one in addition to modal mass and
damping coefficient. In this context, the inherent
differences between model order reduction by modal and by
balanced truncation are being stressed. For the specific
automotive vibration isolation application considered, the
degradation of robust performance and stability is shown to
be insignificant when obtaining a low order controller by
using total force feedback and neglecting flexibility in
the design phase.}
}
@TechReport{ it:2005-002,
author = {Torbj{\"o}rn Wigren},
title = {{MATLAB} Software for Recursive Identification and Scaling
Using a Structured Nonlinear Black-box Model --- Revision
1},
institution = it,
department = syscon,
year = 2005,
number = {2005-002},
month = jan,
note = {The software package can be downloaded from
\url{http://www.it.uu.se/research/publications/reports/2005-002/NRISoftware.zip}}
,
abstract = {This reports is intended as a users manual for a package
of MATLAB scripts and functions, developed for recursive
prediction error identification of nonlinear state space
systems. The core of the package is an implementation of an
output error identification and scaling algorithm. The
algorithm is based on a continuous time, structured black
box state space model of a nonlinear system. The software
can only be run off-line, i.e. no true real time operation
is possible. The algorithm is however implemented so that
true on-line operation can be obtained by extraction of the
main algorithmic loop. The user must then provide the real
time environment. The software package contains scripts and
functions that allow the user to either input live
measurements or to generate test data by simulation. The
scripts and functions for the setup and execution of the
identification algorithm are somewhat more general than
what is described in the references. There is e.g. support
for automatic re-initiation of the algorithm using the
parameters obtained at the end of a previous identification
run. This allows for multiple runs through a set of data,
something that is useful for data sets that are too short
to allow convergence of the algorithm.The re-initiation
step also allows the user to modify the degrees of the
polynomial model structure and to specify terms that are to
be excluded from the model. This makes it possible to
iteratively re-fine the estimated model using multiple
runs. The functionality for display of results include
scripts for plotting of data, parameters, prediction
errors, eigenvalues and the condition number of the
Hessian. The estimated model obtained at the end of a run
can be simulated and the model output plotted, alone or
together with the data used for identification. Model
validation is supported by two methods apart from the
display functionality. First, calculation of the RPEM loss
function can be performed, using parameters obtained at the
end of an identification run. Secondly, the accuracy as a
function of the output signal amplitude can be assessed.}
}
@TechReport{ it:2005-001,
author = {Henrik Brand{\'e}n and Per Sundqvist},
title = {Preconditioners Based on Fundamental Solutions},
institution = it,
department = tdb,
year = 2005,
number = {2005-001},
month = jan,
note = {Revised version of IT technical report 2000-032},
abstract = {We consider a new preconditioning technique for the
iterative solution of linear systems of equations that
arise when discretizing partial differential equations. The
method is applied to finite difference discretizations, but
the ideas apply to other discretizations too.
If $E$ is a fundamental solution of a differential operator
$P$, we have \mbox{$E\ast(Pu)=u$.} Inspired by this, we
choose the preconditioner to be a discretization of an
approximative inverse $K$, given by \[
(Ku)(x)=\int_{\Omega}E(x-y)u(y)dy, \qquad
x\in\Omega\subset\mathds{R}^d, \] where $\Omega$ is the
domain of interest.
We present analysis showing that if $P$ is a first order
differential operator, $KP$ is bounded, and numerical
results show grid independent convergence for first order
partial differential equations, using fixed point
iterations.
For the second order convection-diffusion equation
convergence is no longer grid independent when using fixed
point iterations, a result that is consistent with our
theory. However, if the grid is chosen to give a fixed
number of grid points within boundary layers, the number of
iterations is independent of the physical viscosity
parameter. Also, if GMRES is used together with the
proposed preconditioner, the numbers of iterations decrease
as the grid is refined, also for fixed viscosity.}
}
@TechReport{ it:2004-058,
author = {Anna Eckerdal},
title = {On the Understanding of {O}bject and {C}lass},
institution = it,
department = tdb,
year = 2004,
number = {2004-058},
month = dec,
abstract = {This paper presents the results from a phenomenographic
study of first year university students' understandings of
the concepts \emph{object} and \emph{class}. The students
had just finished their first programming course using Java
as the programming language. The analyses of the study
display qualitatively different ways to understand the
concepts. These aspects of the understandings are
formulated as \emph{categories of description}. Each aspect
is important and relevant when solving a programming task,
and a good understanding includes all aspects of the
concepts. The categories show understandings of different
complexity. There are students who can only express an
understanding of the concepts as code and syntax rules.
Other students can also express the role the objects play
for the programmer and the performance of the task given,
and classes as abstract data types. The students who
express the richest understanding includes the
understandings already mentioned, but they can also express
that classes and objects depicts the real world.
Learning to understand a phenomenon means, in a
phenomenographic perspective, to \emph{discern} new aspects
of that phenomenon. This discernment is only possible if
there is a \emph{variation} in a dimension that corresponds
to the aspect, critical for the specific understanding. The
question of variation gives interesting implications for
teaching discussed in the paper. The discernment requires
the students to have a mindful kind of learning,
\emph{reflective learning}. This implies for the teachers
that \emph{explicitness} in the teaching is of great
importance. Explicitness in the teaching is defined at
several levels, not only that the different aspects of the
understandings found in the study should explicitly be
mentioned, but also explicitness in the explanation and
variation of these aspects.
The importance of offering a broad context for object
oriented programming is also emphasized. This can include
explaining not only the object oriented paradigm, but also
to discuss some other programming paradigms, and the
historical background that lead to these paradigms. It can
also include giving the students the opportunity to follow
a whole programming task with analysis of the problem, and
to design, implement and test the program even at an early
stage of their education.
The paper also includes some examples how the results from
the study can be implemented in the teaching to help the
students in their learning process.}
}
@TechReport{ it:2004-057,
author = {Erik Bor{\"a}lv},
title = {Evaluation and Reflections on the Design of the {WeAidU}
System},
institution = it,
department = hci,
year = 2004,
number = {2004-057},
month = dec,
abstract = {The Web-Based Artificial Intelligence for Diagnostic Use
(WeAidU) system is a support system providing near
instantaneous professional aid in clinical decision making.
The system involves neural networks trained to interpret
myocardial perfusion scintigrams, and enhance the
effectiveness of clinical decision making when it comes to
coronary artery disease. The system is designed to work on
the Internet in a client/server setup . The usability of
the system is evaluated. The evaluation result is related
to two previous evaluations. A link is made from evaluation
results to the way the system is designed and developed. It
is observed that some of the usability problems found are
tied to the development process. Usability inspections
locate a number of possible problem areas when it comes to
the user interaction. At the same time the user's
assessment of usability is satisfactory or even high. This
is most likely explained by the novel nature of this
computer support and a very committed user group.
Clinical physiology is acknowledged to be a computerized
field, where physician's acceptability and use of computers
is fairly high. It is observed that the development team's,
in this particular context, favored a view of usability as
a quality of the product before the view of usability as
integrated in the development process/product. A more
integrated view of usability is suggested to remove
usability errors and integration barriers, and to help the
system better fit into the physician's daily routines.}
}
@TechReport{ it:2004-056,
author = {Erik Bor{\"a}lv},
title = {Design and Evaluation of the {CHILI} System},
institution = it,
department = hci,
year = 2004,
number = {2004-056},
month = dec,
abstract = {The CHILI system is a general-purpose radiology
workstation with teleradiology and telecardiology
functions. The design of the CHILI user interface is made
with the purpose to achieve high usability. Usability is
treated as part of the product develop-ment process instead
of being a separate activity. A number of design principles
-- rationale -- guided the design of the user interface.
The minimalism of the system comes from the approach to
focus primarily on work tasks instead of functionality.
This is accomplished by displaying as much information as
possible in one single window. No functions are out of
sight in menus or additional dialogue windows.
An evaluation using questionnaires was performed to assess
the usability of the system. The questionnaires include a
validated usability measure (the System Usability Scale) to
give a global assessment of system usability. Five
experienced users were interviewed individually to
complement the ques-tionnaire data. The design approach
used in the CHILI system was found to be working, both from
an experienced and new user's perspective. The strong sides
of the system are the ease of use, the minimalism of the
design, and the way the system is adapted to the working
environment. Areas where it is possible to improve are the
on-line help system, questions regarding available
functionality, and user training. Continuous redesign and
development has helped increase usability.}
}
@TechReport{ it:2004-055,
author = {Per L{\"o}tstedt and Jonas Persson and von Sydow, Lina and
Johan Tysk},
title = {Space-Time Adaptive Finite Difference Method for
{E}uropean Multi-Asset Options},
institution = it,
department = tdb,
year = 2004,
number = {2004-055},
month = dec,
abstract = {The multi-dimensional Black-Scholes equation is solved
numerically for a European call basket option using \emph{a
priori}--\emph{a posteriori} error estimates. The equation
is discretized by a finite difference method on a Cartesian
grid. The grid is adjusted dynamically in space and time to
satisfy a bound on the global error at the expiry date. The
discretization errors in each time step are estimated and
weighted by the solution of the adjoint problem. Bounds on
the local errors and the adjoint solution are obtained by
the maximum principle for parabolic equations. The
performance of the method is illustrated by examples in
one, two, three, and four dimensions.}
}
@TechReport{ it:2004-054,
author = {Lars Ferm and Per L{\"o}tstedt and Paul Sj{\"o}berg},
title = {Adaptive, Conservative Solution of the {F}okker-{P}lanck
Equation in Molecular Biology},
institution = it,
department = tdb,
year = 2004,
number = {2004-054},
month = nov,
abstract = {The Fokker-Planck equation on conservation form is
discretized by a finite volume method and advanced in time
by a linear multistep method. The grid cells are refined
and coarsened in blocks of the grid depending on an
estimate of the spatial discretization error and the time
step is chosen to satisfy a tolerance on the temporal
discretization error. The solution is conserved across the
block boundaries so that the total probability is constant.
A similar effect is achieved by rescaling the solution. The
steady state solution is determined as the eigenvector
corresponding to the zero eigenvalue. The method is applied
to the solution of a problem with two molecular species and
the simulation of a circadian clock. Comparison is made
with a stochastic method.}
}
@TechReport{ it:2004-053,
author = {Bharath Bhikkaji and Kaushik Mahata and Torsten
S{\"o}derstr{\"o}m},
title = {Recursive Algorithms for Estimating the Parameters in a
One Dimensional Heat Diffusion System: Analysis},
institution = it,
department = syscon,
year = 2004,
number = {2004-053},
month = nov,
abstract = {In [5], we have proposed two recursive algorithms in the
frequency domain to estimate the parameters of a one
dimensional heat diffusion system. There in, we have
discussed in detail the construction and the implementation
of the algorithms. Further in [5], we observed the
convergence of the proposed algorithms using certain
numerical examples. In this paper, we analyse the
convergence of these algorithms from a theoretical
perspective.}
}
@TechReport{ it:2004-052,
author = {Bharath Bhikkaji and Torsten S{\"o}derstr{\"o}m and
Kaushik Mahata},
title = {Recursive Algorithms for Estimating the Parameters in a
One Dimensional Heat Diffusion System: Derivation and
Implementation},
institution = it,
department = syscon,
year = 2004,
number = {2004-052},
month = nov,
abstract = {In this paper we consider a one-dimensional heat diffusion
system, which is modeled by a partial differential equation
(PDE) involving some unknown parameters. Here we estimate
these unknown parameters recursively using a frequency
domain approach.}
}
@TechReport{ it:2004-051,
author = {Claes Olsson},
title = {Comparative Study of Recursive Parameter Estimation
Algorithms with Application to Active Vibration Isolation},
institution = it,
department = syscon,
year = 2004,
number = {2004-051},
month = nov,
abstract = {In this paper, adaptive filtering is adopted for active
automotive engine vibration isolation where both transient
and stationary engine internal excitations as well as
structure flexibility are considered.
The adaptive filtering problem is formulated using a linear
regression model representation. This allows for an
application of a general family of state-of-the-art
recursive parameter estimation algorithms. The performance
of two specific members of this family has been compared.
Those are the well-known normalised least mean square
(NLMS) algorithm and a recently suggested Kalman filter
based algorithm originally proposed as a method to avoid
covariance windup, here referred to as Stenlund-Gustafsson
(SG). A virtual non-linear 43 degrees of freedom engine and
subframe suspension model and measurement based engine
excitation are used in evaluation of algorithm performance.
With respect to trade-off between convergence and
steady-state variance, the difference Riccati equation
included in SG implies superior performance of SG compared
to NLMS. However, none of the proposed algorithms provide
sufficient tracking performance to deal with transient
engine excitation corresponding, for instance, to rapid
acceleration of the car. In this case, the adaptive
filtering strategy is found to be inadequate.}
}
@TechReport{ it:2004-050,
author = {Stefan Johansson},
title = {High Order Summation by Parts Operator Based on a {DRP}
Scheme Applied to {2D} Aeroacoustics},
institution = it,
department = tdb,
year = 2004,
number = {2004-050},
month = oct,
abstract = {A strictly stable high order finite difference method
based on Tam and Webb's dispersion relation preserving
scheme in the interior has been verified for a 2D
aeroacoustic problem. Results show that the method gives
lower dispersion error than a similar method derived by
Strand, which is based on standard sixth order difference
approximation in the interior, when boundary effects are
not important.}
}
@TechReport{ it:2004-049,
author = {Erik Bor{\"a}lv and Niklas Johansson and Emmanuel
Papaioannou and Athanasios Demiris},
title = {A Design Case: Interactive Sports Content Broadcasting},
institution = it,
department = hci,
year = 2004,
number = {2004-049},
month = oct,
abstract = {Digital television is a new and interesting platform for
developing multimedia services. The MELISA platform aims at
cross-media broadcasting over digital television and 3G
mobile networks. The platform provides presentation of
interactive video content, advertisement and gaming.
The devices targeted by these services are Set-Top Boxes
and Portable Digital Assistants. A new service, in
combination with technology that does not yet allow for
very rich interaction, requires careful and inventive
design of the user interfaces. The key to gaining consumer
acceptance of interactive TV is ease of use.
In this paper we present the system architecture briefly
and discuss issues related to user interface design,
considering both the type of media content and hardware
platforms. We reflect on the design process used and its
suitability as we as designers have experienced it.}
}
@TechReport{ it:2004-048,
author = {Henrik L{\"o}f and Jarmo Rantakokko},
title = {Algorithmic Optimizations of a Conjugate Gradient Solver
on Shared Memory Architectures},
institution = it,
department = tdb,
year = 2004,
number = {2004-048},
month = oct,
abstract = {OpenMP is an architecture-independent language for
programming in the shared memory model. OpenMP is designed
to be simple and powerful in terms of programming
abstractions. Unfortunately, the architecture-independent
abstractions sometimes come with the price of low parallel
performance. This is especially true for applications with
unstructured data access pattern running on distributed
shared memory systems (DSM). Here proper data distribution
and algorithmic optimizations play a vital role for
performance. In this article we have investigated ways of
improving the performance of an industrial class conjugate
gradient (CG) solver, implemented in OpenMP running on two
types of shared memory systems.
We have evaluated bandwidth minimization, graph
partitioning and reformulations of the original algorithm
reducing global barriers. By a detailed analysis of barrier
time and memory system performance we found that bandwidth
minimization is the most important optimization reducing
both L2 misses and remote memory accesses. On an uniform
memory system we get perfect scaling. On a NUMA system the
performance is significantly improved with the algorithmic
optimizations leaving the system dependent global reduction
operations as a bottleneck.}
}
@TechReport{ it:2004-047,
author = {Iordanis Kavathatzopoulos and Jenny {\"O}hman Persson and
Carl {\AA}borg},
title = {Assessing Health and Moral Stress in {IT}-Based Work},
institution = it,
department = hci,
year = 2004,
number = {2004-047},
month = oct,
abstract = {Health and Moral Stress Questionnaire (HMSQ) was
constructed with the aim to assess organizational learning
processes and individual skills necessary for the handling
of problems connected to five areas of activity: work
demands, work task control, support, computer tool use, and
ethics. The main hypothesis was that the existence of
organizational learning processes and individual skills
contributes to lower levels of stress by providing the
knowledge needed to solve the problems arising during
IT-supported work. The results showed that it is possible
to construct a questionnaire to assess organizational
learning and personal skills as a factor defining stress
level at IT-based work. High levels of reliability were
obtained. In accordance to our hypothesis five factors
could be discerned as well as an underlying factor
representing learning processes and personal skills.}
}
@TechReport{ it:2004-046,
author = {Per Carlsson},
title = {Market Simulations},
institution = it,
department = csd,
year = 2004,
number = {2004-046},
month = oct,
abstract = {Supply and demand for electricity show conciderable
fluctuations with season and time of day.
Novel market-based methods for supply -- demand matching
are currently investigated in a European project. This
report covers simulations under preparation as well as the
outcome of a first simulation on the time-scale of
day-ahead power markets.}
}
@TechReport{ it:2004-045,
author = {Per Carlsson and Arne Andersson},
title = {A Flexible Model for Tree-Structured Multi-Commodity
Markets},
institution = it,
department = csd,
year = 2004,
number = {2004-045},
month = oct,
abstract = {In this article we study tree-structured multi-commodity
markets. The concept is a way to handle dependencies
between commodities on the market in a tractable way. The
winner determination problem of a general combinatorial
market is well known to be NP-hard. It has been shown that
on single-unit single-sided auctions with tree-structured
bundles the problem can be computed in polynomial time.
We show that it is possible to extend this to multi-unit
double-sided markets. Further it is possible to handle the
commodities of a bundle not only as complements but as
perfect substitutes too. Under certain conditions the
computation time is still polynomial.}
}
@TechReport{ it:2004-044,
author = {Erik Cedheim and Ramzi Ferchichi and Anders Jonsson and
Dan Lind and Henrik Nyman and Olof Sivertsson and Andreas
Widenfalk and J{\"o}ns {\AA}kerlund and Leonid Mokrushin
and Paul Pettersson},
title = {Kelb - A Real-Time Programming Environment for the {Sony}
{Aibo}},
institution = it,
department = docs,
year = 2004,
number = {2004-044},
month = oct,
abstract = {Kelb is a new real-time programming environment developed
at Uppsala University for the Sony AIBO ERS-210. It is
aimed to provide efficiency by introducing a notion of
light-weight tasks executing according to well-known
real-time scheduling algorithms and resource protocols,
while still allowing applications to be developed in a
high-level abstract programming language. In this paper we
give an overview of the design of Kelb and describe the
status of the environment, currently including: a real-time
programming language and compiler extending gcc for MIPS
with support for time- and event-triggered tasks, a runtime
library with support for static and dynamic preemptive
scheduling algorithms (e.g. fixed priority and earliest
deadline first), and a prototype connection to the Times
tool allowing Kelb designs to be analysed for
schedulabilty.}
}
@TechReport{ it:2004-043,
author = {Iordanis Kavathatzopoulos and Jenny Persson and Carl
{\AA}borg},
title = {Skattekontoret i Falun: Ett m{\"o}nsterkontor},
institution = it,
department = hci,
year = 2004,
number = {2004-043},
month = oct,
note = {In Swedish. Originally written 2002},
abstract = {Denna rapport {\"a}r en utv{\"a}rdering av
{\aa}tg{\"a}rder som genomf{\"o}rdes p{\aa}
skattemyndighetens kontor i Falun som en del av
m{\"o}nsterkontorsprojektet. {\AA}tg{\"a}rdernas syfte var
att tillf{\"o}ra individer och organisation
f{\"a}rdighetsbaserat l{\"a}rande f{\"o}r att minska
otrivsel, stress och oh{\"a}lsa. Avdelningen f{\"o}r
m{\"a}nniska-datorinteraktion vid Uppsala universitet har
deltagit som st{\"o}d i anstr{\"a}ngningarna f{\"o}r
f{\"o}rb{\"a}ttring av arbetsmilj{\"o}n samt i
utv{\"a}rderingen av genomf{\"o}rda {\aa}tg{\"a}rder som en
del i VERKA-projektet. Utv{\"a}rderingen har baserats
p{\aa} data som har samlats genom intervjuer,
fr{\aa}geformul{\"a}r och testinstrument. Resultaten visar
att st{\"a}mningen p{\aa} Falunkontoret {\"a}r b{\"a}ttre
nu {\"a}n innan. De anst{\"a}llda har en klar {\"o}nskan
att till{\"a}mpa det de l{\"a}rt sig samt att forts{\"a}tta
med nya och kompletterande {\aa}tg{\"a}rder. De har
ocks{\aa} ett stort behov att f{\"o}rb{\"a}ttra IT-st{\"o}det.}
}
@TechReport{ it:2004-042,
author = {Per Sundqvist},
title = {Boundary Summation Equations},
institution = it,
department = tdb,
year = 2004,
number = {2004-042},
month = sep,
abstract = {A new solution method for systems of partial difference
equations is presented. It can be seen as a discrete
counterpart of boundary integral equations, but with sums
instead of integrals. The number of unknowns in systems of
linear difference equations with constant coefficients
defined on uniform $d$-dimensional grids are reduced so
that one dimension is eliminated.
The reduction is obtained using fundamental solutions of
difference operators, yielding a reduced system that is
dense. The storage of the reduced system requires
$\mathcal{O}(N)$ memory positions, where $N$ is the length
of the original vector of unknowns. The application of the
matrix utilizes fast Fourier transform as its most complex
operation, and requires hence $\mathcal{O}(N\log N)$
arithmetic operations.
Numerical experiments are performed, exploring the behavior
of GMRES when applied to reduced systems originating from
discretizations of partial differential equations. Model
problems are chosen to include scalar equations as well as
systems, with various boundary conditions, and on
differently shaped domains. The new solution method
performs well for an upwind discretization of an inviscid
flow-problem.
A proof of grid independent convergence is given for a
simpler iterative method applied to a specific
discretization of a first order differential equation. The
numerical experiments indicate that this property carries
over to many other problems in the same class. }
}
@TechReport{ it:2004-041,
author = {Paul Pettersson and Wang Yi (Eds.)},
title = {Proceedings of the 16th Nordic Workshop on Programming
Theory},
institution = it,
department = docs,
year = 2004,
number = {2004-041},
month = oct,
abstract = {The objective of the Nordic Workshop on Programming Theory
is to bring together researchers from (but not limited to)
the Nordic and Baltic countries interested in programming
theory, in order to improve mutual contacts and cooperation.
The 16\emph{th} Nordic Workshop on Programming Theory took
place at the Uppsala University, Sweden, 6-8 October 2004.
The previous workshops were held in Uppsala (1989 and
1999), Aalborg (1990), Gothenburg (1991 and 1995), Bergen
(1992 and 2000), Turku (1993, 1998, and 2003), Aarhus
(1994), Oslo (1996), Tallinn (1997 and 2002), and in Lyngby
(2001).
There were 39 regular presentations at the workshop,
arranged in two parallel sessions. In addition the
following five invited speakers gave presentations in
plenary sessions: Erik Hagersten (Uppsala Univ., Sweden),
Neil D. Jones (Copenhagen Univ., Denmark), Kim G. Larsen
(Aalborg Univ., Denmark), P.S. Thiagarajan (National
University of Singapore), and Michael Williams (Ericsson,
Sweden). }
}
@TechReport{ it:2004-040,
author = {Magnus Sv{\"a}rd and Jan Nordstr{\"o}m},
title = {On the Order of Accuracy for Difference Approximations of
Initial-Boundary Value Problems},
institution = it,
department = tdb,
year = 2004,
number = {2004-040},
month = sep,
abstract = {Finite difference approximations of the second derivative
in space appearing in, parabolic, incompletely parabolic
systems of, and second order hyperbolic, partial
differential equations are considered. If the solution is
pointwise bounded, we prove that finite difference
approximations of those classes of equations can be closed
with two orders less accuracy at the boundary without
reducing the global order of accuracy.
This result is generalised to initial-boundary value
problems with an $m$th order principal part. Then, the
boundary accuracy can be lowered $m$ orders.
Further, it is shown that summation-by-parts operators with
approximating second derivatives are pointwise bounded.
Linear and nonlinear computations corroborates the
theoretical results.}
}
@TechReport{ it:2004-039,
author = {Jing Gong and Jan Nordstr{\"o}m},
title = {A Stable Hybrid Method for Hyperbolic Problems},
institution = it,
department = tdb,
year = 2004,
number = {2004-039},
month = sep,
abstract = {A stable hybrid method that combines the unstructured
finite volume method with high order finite difference
methods have been developed. The coupling procedure is
based on energy estimates and stability can be guaranteed.
Numerical calculations verify that the hybrid method is
efficient and accurate.}
}
@TechReport{ it:2004-038,
author = {Martin Nilsson},
title = {Different Methods that Reduce Cost in Monostatic {RCS}
Computations for {MOM} Accelerated by {MLFMA}},
institution = it,
department = tdb,
year = 2004,
number = {2004-038},
month = sep,
note = {To appear in Proceedings of EMB04 - Computational
Electromagnetics - Methods and Applications, October 18-19,
2004},
abstract = {The problem of computing the monostatic Radar Cross
Section with the Method of Moments accelerated by the
multilevel Fast Multipole algorithm is considered. For
electrically large objects the problem becomes too
expensive in terms of computational work. This paper
suggests two methods that can reduce the work, the Minimal
Residual Interpolation method and a new fast approximate
method related to the Fast Physical Optics method.
Numerical experiments show that the new method gives
reasonable results, while reducing the work substantially
for large objects.}
}
@TechReport{ it:2004-037,
author = {Torsten S{\"o}derstr{\"o}m and Mei Hong},
title = {Identification of Dynamic Errors-in-Variables Systems with
Periodic Data},
institution = it,
department = syscon,
year = 2004,
number = {2004-037},
month = aug,
abstract = {Using instrumental variable methods to estimate the
parameters of dynamic errors-in-variables systems with a
periodic input signal is the focus in this report. How to
choose suitable instrumental variable vectors is the key
point. Four variants are proposed; all of them can generate
consistent estimates. An analysis shows that the best
accuracy is achieved by using a specific overdetermined
instrumental variable vector. Numerical illustrations
demonstrate the effectiveness of the proposed IV3 method
for both white and colored measurement noise. It is
superior to alternative methods under low signal to noise
ratios.}
}
@TechReport{ it:2004-036,
author = {Stefan Johansson},
title = {High Order Finite Difference Operators with the Summation
by Parts Property Based on {DRP} Schemes},
institution = it,
department = tdb,
year = 2004,
number = {2004-036},
month = aug,
abstract = {Strictly stable high order finite difference methods based
on Tam and Webb's dispersion relation preserving schemes
have been constructed. The methods have been implemented
for a 1D hyperbolic test problem, and the theoretical order
of accuracy is observed.}
}
@TechReport{ it:2004-035,
author = {Emad Abd-Elrady and Torsten S{\"o}derstr{\"o}m},
title = {Bias Analysis in Least Squares Estimation of Periodic
Signals Using Nonlinear {ODE}'s},
institution = it,
department = syscon,
year = 2004,
number = {2004-035},
month = aug,
abstract = {Periodic signals can be modeled by means of second-order
nonlinear ordinary differential equations (ODE's). The
right hand side function of the ODE is parameterized in
terms of known basis functions. The least squares algorithm
developed for estimating the coefficients of these basis
functions gives biased estimates, especially at low signal
to noise ratios. This is due to noise contributions to the
periodic signal and its derivatives evaluated using finite
difference approximations. In this paper an analysis for
this bias is given.}
}
@TechReport{ it:2004-034,
author = {Parosh Abdulla and Pritha Mahata and Richard Mayr},
title = {Decidability of Zenoness, Token Liveness and Boundedness
of Dense-Timed Petri Nets},
institution = it,
department = docs,
year = 2004,
number = {2004-034},
month = aug,
note = {To appear in FSTTCS '04},
abstract = {We consider 'Timed Petri Nets (TPNs)' : extensions of
Petri nets in which each token is equipped with a
real-valued clock. We consider the following three
verification problems for TPN.
(i) 'Zenoness:' whether there is an infinite computation
from a given marking which takes only a finite amount of
time. We show decidability of zenoness for TPNs, thus
solving an open problem from \cite{Escrig:etal:TPN}.
(ii) 'Token liveness:' whether a token is {\it alive} in a
marking, i.e., whether there is a computation from the
marking which eventually consumes the token. We show
decidability of the problem by reducing it to the
'coverability problem', which is decidable for TPNs.
(iii) 'Boundedness:' whether the size of the reachable
markings is bounded. We consider two versions of the
problem; namely 'semantic boundedness' where only live
tokens are taken into consideration in the markings, and
'syntactic boundedness' where also dead tokens are
considered. We show undecidability of semantic boundedness,
while we prove that syntactic boundedness is decidable
through an extension of the Karp-Miller algorithm.}
}
@TechReport{ it:2004-033,
author = {Parosh Abdulla and Johann Deneux and Pritha Mahata},
title = {Closed, Open and Robust Timed Networks},
institution = it,
department = docs,
year = 2004,
number = {2004-033},
month = aug,
note = {To appear in Infinity '04},
abstract = {We consider verification of safety properties for
parameterized systems of timed processes, so called 'timed
networks'. A timed network consists of a finite state
process, called a controller, and an arbitrary set of
identical timed processes. In [AJ03] it was shown that
checking safety properties is decidable in the case where
each timed process is equipped with a single real-valued
clock. In [ADM04], we showed that this is no longer
possible if each timed process is equipped with at least
two real-valued clocks. In this paper, we study two
subclasses of timed networks: 'closed' and 'open' timed
networks. In closed timed networks, all clock constraints
are non-strict, while in open timed networks, all clock
constraints are strict (thus corresponds to syntactic
removal of equality testing). We show that the problem
becomes decidable for closed timed network, while it
remains undecidable for open timed networks. We also
consider 'robust' semantics of timed networks by
introducing timing fuzziness through semantic removal of
equality testing. We show that the problem is undecidable
both for closed and open timed networks under the robust
semantics.}
}
@TechReport{ it:2004-032,
author = {Malin Ljungberg and Kurt Otto},
title = {Curvilinear Coordinates in a {PDE} Solver Framework;
Validation},
institution = it,
department = tdb,
year = 2004,
number = {2004-032},
month = aug,
abstract = {Through the use of object-oriented analysis and design
combined with variability modeling, a highly flexible
software model for the metrics handling functionality of a
PDE solver framework was obtained. This new model was
validated against usability goals, particularly with
respect to efficiency and flexibility. The method of
validation together with the results are presented here.
The efficiency of a pilot implementation is comparable to,
in parts even higher than, that of a pre-existing
application-specific reference code. With regards to
flexibility it is shown that the new software model
performs well for a set of four change scenarios selected
by an expert user group.}
}
@TechReport{ it:2004-031,
author = {Malin Ljungberg},
title = {Curvilinear Coordinates in a {PDE} Solver Framework;
Analysis},
institution = it,
department = tdb,
year = 2004,
number = {2004-031},
month = aug,
abstract = {In the present work we demonstrate how the use of an
object oriented analysis and design process, augmented by
variability modeling and user centered design, results in a
flexible software model for handling curvilinear
coordinates in a finite difference PDE solver framework. It
is shown that feature and variability modeling are
appropriate tools for identifying and achieving the
appropriate flexibility in this model.
The resulting software model is validated through an
comparative analysis involving a range of other similar
models.}
}
@TechReport{ it:2004-030,
author = {Wendy Kress and Per L{\"o}tstedt},
title = {Time Step Restrictions using Semi-Implicit Methods for the
Incompressible Navier-Stokes Equations},
institution = it,
department = tdb,
year = 2004,
number = {2004-030},
month = jul,
abstract = {The incompressible Navier-Stokes equations are discretized
in space and integrated in time by the method of lines and
a semi-implicit method. In each time step a set of systems
of linear equations has to be solved. The size of the time
steps are restricted by stability and accuracy of the
time-stepping scheme, and convergence of the iterative
methods for the solution of the systems of equations. The
stability is investigated with a linear model equation
derived from the Navier-Stokes equations. The resolution in
space and time is estimated from turbulent flow physics.
The convergence of the iterative solvers is studied using
the same model equation. The stability constraints and the
convergence rate obtained from the model equation are
compared to results for a semi-implicit integrator of the
Navier-Stokes equations with good agreement. The most
restrictive bound on the time step is given by accuracy,
stability, or convergence depending on the flow conditions
and the numerical method.}
}
@TechReport{ it:2004-029,
author = {Krister {\AA}hlander and Hans Munthe-Kaas},
title = {On Applications of the Generalized Fourier Transform in
Numerical Linear Algebra},
institution = it,
department = tdb,
year = 2004,
number = {2004-029},
month = jul,
abstract = {Matrices equivariant under a group of permutation matrices
are considered. Such matrices typically arise in numerical
applications where the computational domain exhibits
geometrical symmetries. In these cases, group
representation theory provides a powerful tool for block
diagonalizing the matrix via the Generalized Fourier
Transform. This technique yields substantial computational
savings in problems such as solving linear systems,
computing eigenvalues and computing analytic matrix
functions.
The theory for applying the Generalized Fourier Transform
is explained, building upon the familiar special (finite
commutative) case of circulant matrices being diagonalized
with the Discrete Fourier Transform. The classical
convolution theorem and diagonalization results are
generalized to the non-commutative case of block
diagonalizing equivariant matrices.
Our presentation stresses the connection between
multiplication with an equivariant matrices and the
application of a convolution. This approach highlights the
role of the underlying mathematical structures such as the
group algebra, and it also simplifies the application of
\textit{fast} Generalized Fourier Transforms. The theory is
illustrated with a selection of numerical examples.}
}
@TechReport{ it:2004-028,
author = {Lars-Henrik Eriksson},
title = {Using Formal Methods in a Retrospective Safety Case},
institution = it,
department = csd,
year = 2004,
number = {2004-028},
month = jul,
note = {Accepted for publication in the Proceedings of the 23rd
International Conference on Computer Safety, Reliability
and Security (SAFECOMP'04)},
abstract = {Today the development of safety-critical systems is to a
large extent guided by standards that make demands on both
development process and system quality. Before the advent
of these standards, development was typically done on a
``best practise'' basis which could differ much between
application areas. Some safety-critical systems (e.g.
railway interlockings) have a long technical and economical
lifetime so that today we have many legacy safety-critical
systems in operation which were developed according to
practises that would be regarded as unacceptable today.
Usually, such systems are allowed to continue operating by
virtue of past performance. If there is doubt about the
integrity of a legacy system, an alternative to replacement
could be making a ``retrospective'' safety case
demonstrating that the legacy system is indeed safe to use.
Using as example a case taken from railway signalling, we
will show how formal verification can be used in a
retrospective safety case. In this application of formal
methods several particular problems arise, such as
uncertainty about the original requirements and the
required safety level of the various system functions. We
will discuss such problems and the approach taken to deal
with them in the example case.}
}
@TechReport{ it:2004-027,
author = {Thorild Sel{\'e}n},
title = {Reorganisation in the Skewed-Associative {TLB}},
institution = it,
department = docs,
year = 2004,
number = {2004-027},
month = jun,
note = {M.Sc. thesis},
abstract = {One essential component and a common bottleneck in current
virtual memory systems is the \emph{translation lookaside
buffer} (TLB), a small, specialised cache that speeds up
memory accesses by storing recently used address
translations. A TLB can be viewed as a hash table that only
has the capacity for holding a subset of the actively used
address translations.
The traditional way to increase the performance of a TLB
(other than making it larger) is to increase associativity,
typically performing multiple comparisons in parallel to
avoid slowing down lookups; however, this is expensive in
terms of chip area and energy consumption. Skewed
associativity, i.e. using several different hash functions
for parallel lookups, has been demonstrated to yield good
results with less parallelism and therefore at a lower cost.
In skewed-associative models, the sets of possible
placements for two entries may only partially overlap.
Thus, the current placement of entries will limit future
replacement possibilities. This is an inherent
inflexibility in traditional skewed-associative models,
since we cannot predict which placements will enable the
most desirable future replacement choices.
This thesis demonstrates how the performance of
skewed-associative TLB models can be enhanced further by
\emph{reorganisation} --- moving old entries around to
allow for more efficient replacements. This gives even more
efficient usage of TLB locations, increasing performance
without further complicating lookups. The thesis introduces
and demonstrates a \emph{collision tendency} metric that
enables simple comparison of the conflict miss
vulnerability for a multitude of associativity models and
degrees of associativity over a large range of sizes.
Simulations demonstrate that using skewed-associative
techniques and reorganisation, efficient TLBs can be
implemented with far less parallelism in hardware, allowing
for more compact and much less energy-consuming designs
without sacrificing performance.
Additionally, this thesis discusses adapting the
skewed-associative TLB with reorganisation to handle
real-time requirements, notably in applications where tasks
with different real-time needs are run concurrently.}
}
@TechReport{ it:2004-026,
author = {David Lundberg},
title = {Ad Hoc Protocol Evaluation and Experiences of Real World
Ad Hoc Networking},
institution = it,
department = docs,
year = 2004,
number = {2004-026},
month = jun,
note = {M.Sc. thesis},
abstract = {This report give an introduction to ad hoc networking and
presents a list of over 60 ad hoc routing protocols that
have been proposed between 199x and 2002. It also discuss
the problems of performance evaluation of these protocols
and the experiences gathered during the implementation of a
real world evaluation testbed.
A major challenge when evaluating ad hoc routing protocol
proposals is to agree on a metric under which a protocol's
performance will be measured. The fact that most proposed
ad hoc protocols have different goals makes it very
important to find the essential properties and invent
methods how to measure them. This is the main focus in this
this report.
The first part discuss the methods and metrics used in
simulations performed during recent years. The results show
that mobility models, traffic patterns, metrics and
propagation models are crucial when doing simulations in
order to get valid results.
The second part of this paper describes a new metric called
virtual mobility(vM) describing the mobility from a
physical point of view opposed to geometrical or
link-stability metrics. It also describes the APE-testbed
(Ad hoc Protocol Evaluation) that we have created in order
to be a able to conduct large scale experiments in an real
environment.A lot of effort was put on making the testbed
streamlined and as easy to use as possible.}
}
@TechReport{ it:2004-025,
author = {David Lundberg},
title = {Feasibility Study of {WLAN} Technology for the Uppsala -
Stockholm Commuter Train},
institution = it,
department = docs,
year = 2004,
number = {2004-025},
month = jun,
abstract = {The purpose of this study is to investigate different
solutions to provide high speed Internet access on a train
travelling at 200 km/h using WLAN equipment. Every day
about 15000 people commute between Uppsala and Stockholm
and it is reasonable to assume that about 10\% of those
could use the time better on the train if they had a
connection to the Internet. A study~\cite{survey} in the UK
has shown that 80\% of the business travellers work on the
trains and would use WLAN if it was available. At least two
companies in Sweden offer a service for this but they use
expensive technology with low bandwidth.
The aim of this feasibility study is to investigate if it
is possible to build an infrastructure with WLAN equipment
and offer the customer the bandwidth of about a normal
broadband connection at home. The task is also to make
estimations of the costs for different solutions to be help
decide about a continuation of the project.}
}
@TechReport{ it:2004-024,
author = {Mathias Spjuth and Martin Karlsson and Erik Hagersten},
title = {Low Power and Conflict Tolerant Cache Design},
institution = it,
department = docs,
year = 2004,
number = {2004-024},
month = may,
abstract = {The common approach to reduce cache conflicts is to
increase the associativity. From a dynamic cache power
perspective this associativity comes at a high cost. In
this paper we present miss ratio performance and dynamic
power estimates for a skewed cache and also for a new
organization proposed, the elbow cache. The elbow cache
extends the skewed cache organization with a relocation
strategy for conflicting blocks. We show that these skewed
designs significantly reduces the conflict problems while
consuming up to 56\% less dynamic power than a comparably
performing 8-way set-associative cache.}
}
@TechReport{ it:2004-023,
author = {Jarmo Rantakokko},
title = {Interactive Learning of Algorithms},
institution = it,
department = tdb,
year = 2004,
number = {2004-023},
month = may,
note = {Accepted to \emph{Third Program Visualization Workshop}
(PVW'2004)},
abstract = {Visualization is believed to be an effective technique for
learning and understanding algorithms in traditional
computer science. In this paper, we focus on parallel
computing and algorithms. An inherent difficulty with
parallel programming is that it requires synchronization
and coordination of the concurrent activities. We want to
use visualization to help students to understand how the
processors work together in an algorithm and how they
interact through communication. To conceptualize this we
have used two different visualization techniques, computer
animations and role plays. As the students can see how the
processors run simultaneously in parallel, it illustrates
important concepts such as processor load balance,
serialization bottlenecks, synchronization and
communication. The results show that both animations and
role plays are better for learning and understanding
algorithms than the textbook.}
}
@TechReport{ it:2004-022,
author = {Pascal Van Hentenryck and Pierre Flener and Justin Pearson
and Magnus {\AA}gren},
title = {Compositional Derivation of Symmetries for Constraint
Satisfaction},
institution = it,
department = csd,
year = 2004,
number = {2004-022},
month = may,
abstract = {This paper reconsiders the problems of discovering
symmetries in constraint satisfaction problems (CSPs). It
proposes a compositional approach which derives symmetries
of the applications from primitive constraints. Its key
insight is the recognition of the special role of global
constraints in symmetry detection. Once the symmetries of
global constraints are available, it often becomes much
easier to derive symmetries compositionally and
efficiently. The paper demonstrates the potential of this
approach by studying several classes of value and variable
symmetries and applying the resulting techniques to two
non-trivial applications. The paper also discusses the
potential of reformulations and high-level modelling
abstractions to strengthen symmetry discovery.}
}
@TechReport{ it:2004-021,
author = {Erik Berg and Erik Hagersten},
title = {Efficient Data-Locality Analysis of Long-Running
Applications},
institution = it,
department = docs,
year = 2004,
number = {2004-021},
month = may,
abstract = {Analysis of application data cache behavior is important
for program optimization and architectural design
decisions. Current methods include hardware monitoring and
simulation, but these methods lack from either limited
flexibility or large run-time overhead that prevents
realistic workloads. This paper describes a new fast and
flexible tool based on StatCache. This tool is based on a
probabilistic cache model instead of a functional cache
simulator and use sparsely sampled run-time information
instead of complete traces or sampled contiguous subtraces.
A post-run analyzer calculates miss ratios of fully
associative caches of arbitrary size and cache line size,
from statistics gathered at a single run. It can also
produce various data-locality metrics and give
data-structure centric data-locality figures.
The implementation utilizes simple-hardware and
operating-system support available in most operating
systems and runs uninstrumented optimized code. We evaluate
the method using the SPEC benchmark suite using the largest
(ref) input sets and show that the accuracy is high. We
also show the run-time overhead for this flexible ``cache
simulator'' to be less than 20\% for long-running
applications, much faster than current simulators.}
}
@TechReport{ it:2004-020,
author = {Malin Ljungberg and Krister {\AA}hlander},
title = {Generic Programming Aspects of Symmetry Exploiting
Numerical Software},
institution = it,
department = tdb,
year = 2004,
number = {2004-020},
month = may,
note = {To appear in the proceedings of the mini-symposium
``Software Concepts and Free Software for PDEs'' of the
ECCOMAS 2004 congress, Jyv{\"a}skyl{\"a}, Finland, 24-28
July 2004},
abstract = {The use of the generalized Fourier transform as a means to
diagonalize certain types of equivariant matrices, and thus
speeding up the solution of numerical systems, is
discussed. Such matrices may arise in various applications
with geometrical symmetries, for example when the boundary
element method is used to solve an electrostatic problem in
the exterior of a symmetric object. The method is described
in detail for an object with a triangular symmetry, and the
feasibility of the method is confirmed by numerical
experiments.
The design of numerical software for this kind of
applications is a challenge. It is argued that generic
programming is very suitable in this context, mainly
because it is type safe and promotes polymorphism
capabilities in link time.
A generic C++ design of important mathematical abstractions
such as groups, vector spaces, and group algebras, is
outlined, illustrating the potential provided by generative
programming techniques. The integration of explicit support
for various data layouts for efficiency tuning purposes is
discussed. }
}
@TechReport{ it:2004-019,
author = {Owe Axelsson and Maya Neytcheva},
title = {Eigenvalue Estimates for Preconditioned Saddle Point
Matrices},
institution = it,
department = tdb,
year = 2004,
number = {2004-019},
month = may,
abstract = {New eigenvalue bounds for symmetric matrices of saddle
point form are derived and applied for preconditioned
versions of the matrices. The preconditioners enable
efficient iterative solution of the corresponding linear
systems with, for some important applications, an optimal
order of computational complexity.}
}
@TechReport{ it:2004-018,
author = {Emmanuel Papaioannou and Erik Bor{\"a}lv and Athanasios
Demiris and Niklas Johansson and Nikolaos Ioannidis},
title = {User Interface Design for Multi-platform Interactive
Sports Content Broadcasting},
institution = it,
department = hci,
year = 2004,
number = {2004-018},
month = may,
note = {Accepted to AVI 2004 (Advanced Visual Interfaces),
Gallipoli (Lecce), Italy},
abstract = {The new generation of television viewers is currently
being confronted and becoming acquainted with a series of
technological developments in the realm of consumer
electronics and gaming that raise their expectations for
similar advances in TV broadcasts. The MELISA platform aims
at the cross-media broadcasting of sports events featuring
interactive advertising and sports-related games over
digital television and next generation mobile network
infrastructures. The platform provides services for optimal
presentation of complex interactive real time video
content, for advertisement and an advanced real-time gaming
(betting) engine in at least two different client
platforms. User interface design is a major issue in a
complex end-to-end solution having to cater the needs of
users ranging from broadcasting professionals to end-users.
Especially in the case of interactive gaming there are
numerous challenges in the user interface design, in order
to deliver to all categories of devices (and end users)
equal quantity and quality of information. In this paper we
present the overall system architecture and philosophy and
then focus on user interface design issues both for the
routine work of broadcasting professionals as well as the
end users, owners of different types of consumer devices
(such as PDAs and interactive TV Set Top Boxes).}
}
@TechReport{ it:2004-017,
author = {Parosh Aziz Abdulla and Aletta Nylen},
title = {Better-Structured Transition Systems},
institution = it,
department = docs,
year = 2004,
number = {2004-017},
month = apr,
abstract = {In automated verification of infinite-state systems, a
variety of algorithms that operate on constraints
representing sets of states have been developed. Many of
these algorithms rely on well quasi-ordering of the
constraint system for proving termination. A number of
methods for generating new well quasi-ordered constraint
systems have been proposed. However, many of these
constraint systems suffer from constraint explosion as the
number of constraints generated during analysis grows
exponentially with the size of the problem. We suggest
using the theory of better quasi-ordering to prove
termination since that will allow generation of constraint
systems that are less prone to constraint explosion. We
also present a method to derive such constraint systems. We
introduce existential zones, a constraint system for
verification of systems with an unbounded number of clocks
and use our methodology to prove that existential zones are
better quasi-ordered. We show how to use existential zones
in verification of timed Petri nets and present some
experimental results. Finally, we present several other
constraint systems which have been derived using our
methodology.}
}
@TechReport{ it:2004-016,
author = {Maya Neytcheva and Erik B{\"a}ngtsson and Bj{\"o}rn Lund},
title = {Numerical Solution Methods for Glacial Rebound Models},
institution = it,
department = tdb,
year = 2004,
number = {2004-016},
month = apr,
note = {Typographic corrections April 2005},
abstract = {We consider the finite element discretization of the
system of partial differential equations describing the
stress field and the displacements in a (visco)elastic
inhomogeneous layered media in response to a surface load.
The underlying physical phenomenon, which is modelled, is
glacial advance and recession, and the resulting crustal
stress state. We analyse the elastic case in more detail
and present discretization error estimates. The so-obtained
linear system of equations is solved by an iterative
solution method with suitable preconditioning and numerical
experiments are presented.}
}
@TechReport{ it:2004-015,
author = {Magnus {\AA}gren},
title = {Set Variables and Local Search},
institution = it,
department = csd,
year = 2004,
number = {2004-015},
month = apr,
note = {Updated May 2004},
abstract = {Many combinatorial (optimisation) problems have natural
models based on, or including, set variables and set
constraints. This modelling device has been around for
quite some time in the constraint programming area, and
proved its usefulness in many applications. This paper
introduces set variables and set constraints also in the
local search area. It presents a way of representing set
variables in the local search context, where we deal with
concepts like transition functions, neighbourhoods, and
penalty costs. Furthermore, some common set constraints and
their penalty costs are defined. These constraints are
later used to model three problems and some initial
experimental results are reported.}
}
@TechReport{ it:2004-014,
author = {P{\"a}r Samuelson and Bj{\"o}rn Halvarsson and Bengt
Carlsson},
title = {Analysis of the Input-Output Couplings in a Wastewater
Treatment Plant Model},
institution = it,
department = syscon,
year = 2004,
number = {2004-014},
month = apr,
abstract = {This paper considers the problem of channel interaction in
multivariable systems. As an application, nitrate removal
in the activated sludge process in a wastewater treatment
plant is studied. To evaluate the degree of channel
interaction, two different tools are compared; the well
known Relative Gain Array (RGA) and the more recently
developed Hankel Interaction Index Array (HIIA). The
results of the analysis are discussed from a process
knowledge point of view, and are also illustrated with some
control experiments. The main conclusion is that both the
analysis tools provide reasonable results in this case. The
HIIA, however, gives a deeper insight about the actual
cross couplings in the system. This insight may also be
used in order to design suitable structured multivariable
controllers.}
}
@TechReport{ it:2004-013,
author = {Andreas Westling},
title = {Inter-Networking {MPLS} and {SelNet}},
institution = it,
department = docs,
year = 2004,
number = {2004-013},
month = apr,
note = {M.Sc. thesis},
abstract = {The growing amount of traffic on the Internet has lead to
regular IP switching technique becoming more and more
inadequate. Since more IP switching routers have to be
purchased in order to co-operate with the traffic the costs
are rising for the ISPs. This has lead to extensive
research on how to lower the cost for the end-toend
computation. One of the ways in doing so is to use a
tag-switching approach. This thesis will give a brief
introduction to two tag-switching architectures, MPLS and
SelNet, and show how these can co-operate despite their
differences.}
}
@TechReport{ it:2004-012,
author = {Parosh Aziz Abdulla and Johann Deneuz and Pritha Mahata},
title = {Multi-Clock Timed Networks},
institution = it,
department = docs,
year = 2004,
number = {2004-012},
month = apr,
abstract = {We consider verification of safety properties for
parameterized systems of timed processes, so called {\it
timed networks}. A timed network consists of a finite state
process, called a controller, and an arbitrary set of
identical timed processes. In a previous work, we showed
that checking safety properties is decidable in the case
where each timed process is equipped with a single
real-valued clock. It was left open whether the result
could be extended to multi-clock timed networks. We show
that the problem becomes undecidable when each timed
process has two clocks.
On the other hand, we show that the problem is decidable
when clocks range over a discrete time domain. This
decidability result holds when processes have any finite
number of clocks.}
}
@TechReport{ it:2004-011,
author = {Henrik Bj{\"o}rklund and Sven Sandberg and Sergei
Vorobyov},
title = {Randomized Subexponential Algorithms for Infinite Games},
institution = it,
department = csd,
year = 2004,
number = {2004-011},
month = apr,
abstract = {The complexity of solving infinite games, including
parity, mean payoff, and simple stochastic games, is an
important open problem in verification, automata theory,
and complexity theory. In this paper we develop an abstract
setting for studying and solving such games, as well as
related problems, based on function optimization over
certain discrete structures. We introduce new classes of
completely local-global (CLG) and recursively local-global
(RLG) functions, and show that strategy evaluation
functions for parity and simple stochastic games belong to
these classes. We also establish a relation to the
previously well-studied completely unimodal (CU) and
local-global functions. A number of nice properties of
CLG-functions are proved.
In this setting, we survey several randomized optimization
algorithms appropriate for CU-, CLG-, and RLG-functions. We
show that the subexponential algorithms for linear
programming by Kalai and Matousek, Sharir, and Welzl, can
be adapted to optimizing the functions we study, with
preserved subexponential expected running time. We examine
the relations to two other abstract frameworks for
subexponential optimization, the LP-type problems of
Matousek, Sharir, Welzl, and the abstract optimization
problems of G{\"a}rtner. The applicability of our abstract
optimization approach to parity games builds upon a
discrete strategy evaluation measure.
We also consider local search type algorithms, and settle
two nontrivial, but still exponential, upper bounds. As
applications we address some complexity-theoretic issues
including non-PLS-completeness of the problems studied.}
}
@TechReport{ it:2004-010,
author = {Neil Ghani and Kidane Yemane and Bj{\"o}rn Victor},
title = {Relationally Staged Computations in Calculi of Mobile
Processes},
institution = it,
department = docs,
year = 2004,
number = {2004-010},
month = mar,
note = {Accepted for CMCS 2004},
abstract = {We apply the recently developed techniques of higher order
abstract syntax and functorial operational semantics to
give a compositional and fully abstract semantics for the
$\pi$-calculus equipped with open bisimulation. The key
novelty in our work is the realisation that the
sophistication of open bisimulation requires us to move
from the usual semantic domain of presheaves over
subcategories of $\mathbf{Set}$ to presheaves over
subcategories of $\mathbf{Rel}$. This extra structure is
crucial in controlling the renaming of extruded names and
in providing a variety of different dynamic allocation
operators to model the different binders of the
$\pi$-calculus. }
}
@TechReport{ it:2004-009,
author = {Henrik Johansson and Johan Steensland},
title = {A Characterization of a Hybrid and Dynamic Partitioner for
{SAMR} Applications},
institution = it,
department = tdb,
year = 2004,
number = {2004-009},
month = mar,
abstract = {Significantly improving the scalability of large
structured adaptive mesh refinement (SAMR) applications is
challenging. It requires sophisticated capabilities for
using the underlying parallel computer's resources in the
most efficient way. This is non-trivial, since the basic
conditions for how to allocate the resources change
dramatically during run-time due to the dynamics inherent
in these applications.
This report presents a first characterization of a hybrid
and dynamic partitioner for parallel SAMR applications.
Specifically, we determine optimal parameter settings for
trade-offs like communication vs.\ load balance and speed
vs.\ quality. The key contribution is that the
characterization enables the partitioner to respond
accurately to stimuli from system and application state,
and hence adapting to various SAMR scenarios. This
potentially reduces run-time for large SAMR applications.}
}
@TechReport{ it:2004-008,
author = {P{\"a}r Samuelsson and Bengt Carlsson},
title = {An Integrating Linearization Method for Static Input
Nonlinearities},
institution = it,
department = syscon,
year = 2004,
number = {2004-008},
month = mar,
abstract = {This report considers a method for linearization of models
containing static input nonlinearities in series with a
linear model, so called Hammerstein models. The method is
based on exact linearization via internal feedback and is
performed by differentiating the nonlinearity with respect
to the input signal. Using this approach, an integration is
added in the loop gain of the linearized system via the
internal feedback. Standard linear design strategies can be
used in order to construct a control law for the resulting
integrating linearized system. The method presented here
should be seen as an alternative to the standard method
that utilizes the inverse of the static nonlinearity.
Particularly, in cases when analytic inversion is
difficult, the presented method provides an attractive
alternative. An extension of the method where the static
nonlinearity is fed by both the input and output signals is
also presented and illustrated with some simulation
results.}
}
@TechReport{ it:2004-007,
author = {Erik Nordstr{\"o}m and Per Gunningberg and Christian
Tschudin},
title = {Comparison of Gateway Forwarding Strategies in Ad hoc
Networks},
institution = it,
department = docs,
year = 2004,
number = {2004-007},
month = mar,
abstract = {This paper studies the efficient integration of gateway
forwarding strategies in wireless ad hoc networks. The
problem to solve is the forwarding to one or more gateways
in an environment where there is no hierarchical
addressing. We provide an overview of the challenges in
this area and then compare the properties of two proposed
forwarding strategies; traditional default routes and
tunnels. We find that default route forwarding will not
operate efficiently in a multi-hop environment and that it
will, without modifications, operate incorrectly with
multiple gateways. On the other hand, we find tunnel
forwarding to be architecturally appealing with many
properties that make it a suitable forwarding strategy with
multiple gateways. We have implemented default route and
tunnel forwarding in the AODV routing protocol. We verify
in simulation that the incorrect forwarding of default
routes has adverse effects on TCP and that the
modifications we suggest improve performance, although they
do not completely solve the problem. Our simulations also
show that our tunnel implementation is efficient and works
well with TCP, even with multiple gateways.}
}
@TechReport{ it:2004-006,
author = {Henrik L{\"o}f and Markus Nord{\'e}n and Sverker Holmgren},
title = {Improving Geographical Locality of Data for Shared Memory
Implementations of {PDE} Solvers},
institution = it,
department = tdb,
year = 2004,
number = {2004-006},
month = feb,
abstract = {On cc-NUMA multi-processors, the non-uniformity of main
memory latencies motivates the need for co-location of
threads and data. We call this special form of data
locality, \emph{geographical locality}, as the
non-uniformity is a consequence of the physical distance
between the cc-NUMA nodes. In this article, we compare the
well established method of exploiting the first-touch
strategy using parallel initialization of data to an
application-initiated page migration strategy as means of
increasing the geographical locality for a set of important
scientific applications.
Four PDE solvers parallelized using OpenMP are studied; two
standard NAS NPB3.0-OMP benchmarks and two kernels from
industrial applications. The solvers employ both structured
and unstructured computational grids. The main conclusions
of the study are: (1) that geographical locality is
important for the performance of the applications, (2) that
application-initiated migration outperforms the first-touch
scheme in almost all cases, and in some cases even results
in performance which is close to what is obtained if all
threads and data are allocated on a single node. We also
suggest that such an application-initiated migration could
be made fully transparent by letting the OpenMP compiler
invoke it automatically.}
}
@TechReport{ it:2004-005,
author = {H{\aa}kan Zeffer and Zoran Radovic and Oskar Grenholm and
Erik Hagersten},
title = {Evaluation, Implementation and Performance of Write
Permission Caching in the {DSZOOM} System},
institution = it,
department = docs,
year = 2004,
number = {2004-005},
month = feb,
note = {Updated June 2004},
abstract = {Fine-grained software-based distributed shared memory
(SW-DSM) systems typically maintain coherence with in-line
checking code at load and store operations to shared
memory. The instrumentation overhead of this added checking
code can be severe.
This paper (1) shows that most of the instrumentation
overhead in the fine-grained DSZOOM SW-DSM system is store
related, (2) introduces a new write permission cache (WPC)
technique that exploits spatial store locality and batches
coherence actions at runtime, (3) evaluates WPC and (4)
presents WPC results when implemented in a real SW-DSM
system. On average, the WPC reduces the store
instrumentation overhead in DSZOOM with 42~(67) percent for
benchmarks compiled with maximum (minimum) compiler
optimizations.}
}
@TechReport{ it:2004-004,
author = {Torbj{\"o}rn Wigren},
title = {Recursive Prediction Error Identification of Nonlinear
State Space Models},
institution = it,
department = syscon,
year = 2004,
number = {2004-004},
month = jan,
abstract = {A recursive prediction error algorithm for identification
of systems described by nonlinear ordinary differential
equation (ODE) models is presented. The model is a MIMO ODE
model, parameterized with coefficients of a multi-variable
polynomial that describes one component of the right hand
side function of the ODE. It is explained why such a
parameterization is a key to obtain a well defined
algorithm, that does not suffer from singularities and
over-parameterization problems. Furthermore, it is proved
that the selected model can also handle systems with more
complicated right hand side structure, by identification of
an input-output equivalent system in the coordinate system
of the selected states. The linear output measurements can
be corrupted by zero mean disturbances that are correlated
between measurements and over time. The disturbance
correlation matrix is estimated on-line and need not be
known beforehand. The algorithm is applied to live data
from a system consisting of two cascaded tanks with free
outlets. It is illustrated that the identification
algorithm is capable of producing a highly accurate
nonlinear model of the system, despite the fact that the
right hand structure of the system has two nontrivial
nonlinear components. A novel technique based on scaling of
the sampling period that significantly improves the
numerical properties of the algorithm is also disclosed.}
}
@TechReport{ it:2004-003,
author = {Johan Elf and Per L{\"o}tstedt and Paul Sj{\"o}berg},
title = {Problems of High Dimension in Molecular Biology},
institution = it,
department = tdb,
year = 2004,
number = {2004-003},
month = jan,
note = {This paper was presented at the 19th GAMM-Seminar in
Leipzig, January 23-25, 2003.},
abstract = {The deterministic reaction rate equations are not an
accurate description of many systems in molecular biology
where the number of molecules of each species often is
small. The master equation of chemical reactions is a more
accurate stochastic description suitable for small
molecular numbers. A computational difficulty is the high
dimensionality of the equation. We describe how it can be
solved by first approximating it by the Fokker-Planck
equation. Then this equation is discretized in space and
time by a finite difference method. The method is compared
to a Monte Carlo method by Gillespie. The method is applied
to a four-dimensional problem of interest in the regulation
of cell processes.}
}
@TechReport{ it:2004-002,
author = {Pablo Giambiagi and Gerardo Schneider and Frank D.
Valencia},
title = {On the Expressiveness of {CCS}-like Calculi},
institution = it,
department = docs,
year = 2004,
number = {2004-002},
month = jan,
abstract = {In the literature there are several CCS-like process
calculi, or CCS variants, differing in the constructs for
the specification of infinite behavior and in the scoping
rules w.r.t. channel names. In this paper we study various
representatives of these calculi based upon both their
relative expressiveness and the decidability of divergence
(i.e., the existence of a divergent computation). We regard
any two calculi as being equally expressive iff for every
process in each calculus, there exists a weakly bisimilar
process in the other.
By providing weak bisimilarity preserving mappings among
the various variants, we show that in the context of
relabeling-free and finite summation calculi: (1) CCS with
parameterless (or constant) definitions is equally
expressive to the variant with parametric definitions. (2)
The CCS variant with replication is equally expressive to
that with recursive expressions and static scope. We also
state that the divergence problem is undecidable for the
calculi in (1) but decidable for those in (2). We obtain
this from previous (un)decidability results and by showing
the relevant mappings to be computable and to preserve
divergence and its negation. From (1) and the well-known
fact that parametric definitions can replace injective
relabelings, we show that injective relabelings are
redundant (i.e., derived) in CCS (which has constant
definitions only).}
}
@TechReport{ it:2004-001,
author = {Torsten S{\"o}derstr{\"o}m and Torbj{\"o}rn Wigren and
Emad Abd-Elrady},
title = {Maximum Likelihood Modeling of Orbits of Nonlinear
{ODE}s},
institution = it,
department = syscon,
year = 2004,
number = {2004-001},
month = jan,
abstract = {This report treats a new approach to the problem of
periodic signal estimation. The idea is to model the
periodic signal as a function of the state of a second
order nonlinear ordinary differential equation (ODE). This
is motivated by Poincare theory which is useful for proving
the existence of periodic orbits for second order ODEs. The
functions of the right hand side of the nonlinear ODE are
then parameterized, and a maximum likelihood algorithm is
developed for estimation of the parameters of these unknown
functions from the measured periodic signal. The approach
is analyzed by derivation and solution of a system of ODEs
that describes the evolution of the Cramer-Rao bound over
time. The proposed methodology reduces the number of
estimated unknowns at least in cases where the actual
signal generation resembles that of the imposed model. This
in turn is expected to result in an improved accuracy of
the estimated parameters.}
}
@TechReport{ it:2003-065,
author = {Michael Baldamus and Richard Mayr and Gerardo Schneider},
title = {A Backward/Forward Strategy for Verifying Safety
Properties of Infinite-State Systems},
institution = it,
department = docs,
year = 2003,
number = {2003-065},
month = dec,
abstract = {This paper has two main contributions: For one, we
describe a general method for verifying safety properties
of non-well-quasi-ordered infinite-state systems for which
reachability is undecidable in general, the question being
whether a set U of configurations is reachable. In many
cases this problem can be solved as follows: First, one
constructs a well-quasi-ordered overapproximation of the
system in question. Thereby one can compute an
overapproximation of the set Pre*(U) of all predecessors of
U. Second, one performs an exact bounded forward search for
U (starting at the initial state) which always stays inside
the already computed overapproximation of Pre*(U), thus
curbing the search space. This restricted forward search is
more efficient than a normal forward search, yielding
answers of the form YES, NO, or UNKNOWN, where the YES and
NO answers are always correct. As our second main
contribution herein, we apply our method to
relabelling-free CCS with finite summation, which is
already a process calculus for which reachability is
undecidable. To our knowledge, this part is actually the
first application of well-structered systems to verifying
safety properties in process calculi. The application is
done via a special Petri nets semantics for the calculus
that we consider.}
}
@TechReport{ it:2003-064,
author = {Arnim Br{\"u}ger and Bertil Gustafsson and Per
L{\"o}tstedt and Jonas Nilsson},
title = {High Order Accurate Solution of the Incompressible
Navier-Stokes Equations},
institution = it,
department = tdb,
year = 2003,
number = {2003-064},
month = dec,
abstract = {High order methods are of great interest in the study of
turbulent flows in complex geometries by means of direct
simulation. With this goal in mind, the incompressible
Navier-Stokes equations are discretized in space by a
compact fourth order finite difference method on a
staggered grid. The equations are integrated in time by a
second order semi-implicit method. Stable boundary
conditions are implemented and the grid is allowed to be
curvilinear in two space dimensions. In every time step, a
system of linear equations is solved for the velocity and
the pressure by an outer and an inner iteration with
preconditioning. The convergence properties of the
iterative method are analyzed. The order of accuracy of the
method is demonstrated in numerical experiments. The method
is used to compute the flow in a channel, the driven cavity
and a constricted channel.}
}
@TechReport{ it:2003-063,
author = {Michael Baldamus and Joachim Parrow and Bj{\"o}rn Victor},
title = {Spi Calculus Translated to $\pi$-Calculus Preserving
May-Testing},
institution = it,
department = docs,
year = 2003,
number = {2003-063},
month = dec,
abstract = {We present a concise and natural encoding of the
spi-calculus into the more basic $\pi$-calculus and
establish its correctness with respect to a formal notion
of testing. This is particularly relevant for security
protocols modelled in spi since the tests can be viewed as
adversaries. The translation has been implemented in a
prototype tool. As a consequence, protocols can be
described in the spi calculus and analysed with the
emerging flora of tools already available for $\pi$. The
translation also entails a more detailed operational
understanding of spi since high level constructs like
encryption are encoded in a well known lower level. The
formal correctness proof is nontrivial and interesting in
its own; so called context bisimulations and new techniques
for compositionality make the proof simpler and more
concise.}
}
@TechReport{ it:2003-062,
author = {Emilio Tuosto and Bj{\"o}rn Victor and Kidane Yemane},
title = {Polyadic History-Dependent Automata for the Fusion
Calculus},
institution = it,
department = docs,
year = 2003,
number = {2003-062},
month = dec,
abstract = {We extend History Dependent Automata to handle polyadic
labels, and using a new symbolic semantics of fusion
calculus we give a mapping into these Polyadic HDA with
Negative Transitions, and show that the mapping is adequate
with respect to hyperequivalence in the fusion calculus.
This lays the grounds for HD-automata-based tools
applicable not only to the monadic pi-calculus but also to
the fusion calculus and polyadic pi-calculus, allowing
implementation efforts to be focused at a foundational
level rather than being multiplied in several tools.}
}
@TechReport{ it:2003-061,
author = {Lars Ferm and Per L{\"o}tstedt},
title = {Space-Time Adaptive Solution of First Order {PDE}s},
institution = it,
department = tdb,
year = 2003,
number = {2003-061},
month = dec,
abstract = {An explicit time-stepping method is developed for adaptive
solution of time-dependent partial differential equations
with first order derivatives. The space is partitioned into
blocks and the grid is refined and coarsened in these
blocks. The equations are integrated in time by a
Runge-Kutta-Fehlberg method. The local errors in space and
time are estimated and the time and space steps are
determined by these estimates. The error equation is
integrated to obtain global errors of the solution. The
method is shown to be stable if one-sided space
discretizations are used. Examples such as the wave
equation, Burgers' equation, and the Euler equations in one
space dimension with discontinuous solutions illustrate the
method.}
}
@TechReport{ it:2003-060,
author = {Pierre Flener},
title = {Realism in Project-Based Software Engineering Courses:
Rewards, Risks, and Recommendations},
institution = it,
department = csd,
year = 2003,
number = {2003-060},
month = dec,
abstract = {A software engineering course is often the capstone of a
general undergraduate curriculum in computer science. It is
usually at least partly a project-based course, with the
intention that student groups can deploy their already
acquired skills on programming, verification, databases,
and human-computer interaction, while applying the new
material about requirements, architecture, and project
management on a project. I have taught a software
engineering course six times over the last few years, using
a combination of ideas that I have never seen elsewhere,
with a strong emphasis on realism. I here reflect on the
rewards and risks of this approach, and make some
recommendations for future offerings.}
}
@TechReport{ it:2003-059,
author = {Jonas Persson and von Sydow, Lina},
title = {Pricing European Multi-asset Options Using a Space-time
Adaptive FD-method},
institution = it,
department = tdb,
year = 2003,
number = {2003-059},
month = dec,
abstract = {In this paper we present an adaptive technique to solve
the multi-dimensional Black-Scholes equation. The number of
grid-points required for a given tolerance of the local
discretization errors is reduced substantially when
compared to a standard equidistant grid.
Using our adaptive methods in space and time we have
control of the local discretization errors and can refine
the grid where needed for accuracy reasons.}
}
@TechReport{ it:2003-058,
author = {Erik Berg and Erik Hagersten},
title = {StatCache: A Probabilistic Approach to Efficient and
Accurate Data Locality Analysis},
institution = it,
department = docs,
year = 2003,
month = dec,
number = {2003-058},
abstract = {The widening memory gap reduces performance of
applications with poor data locality. This problem can be
analyzed using working-set graphs. Current methods to
generate such graphs include set sampling and time
sampling, but cold start effects and unrepresentative set
selection impair accuracy.
In this paper we present StatCache, a novel sample-based
method that can perform data-locality analysis on realistic
workloads. During the execution of an application, sparse
discrete memory accesses are sampled, and their reuse
distances are measured using a simple watchpoint mechanism.
StatCache uses the information collected from a single run
to accurately estimate miss ratios of fully-associative
caches of arbitrary sizes and generates working-set graphs.
We evaluate StatCache using the SPEC CPU2000 benchmarks and
show that StatCache gives accurate results with a sampling
rate as low as $10^{-4}$. We also provide a
proof-of-concept implementation, and discuss potentially
very fast implementation alternatives.}
}
@TechReport{ it:2003-057,
author = {Erik Berg and Erik Hagersten},
title = {Low-Overhead Spatial and Temporal Data Locality Analysis},
institution = it,
department = docs,
year = 2003,
month = dec,
number = {2003-057},
abstract = {Performance is getting increasingly sensitive to cache
behavior because of the growing gap between processor cycle
time and memory latency. To improve performance,
applications need to be optimized for data locality.
Run-time analysis of spatial and temporal data locality can
be used to facilitate this and should help both manual
tuning and feedback-based compiler optimizations.
Identifying cache behavior of individual data structures
further enhances the optimization process. Current methods
to perform such analysis include simulation combined with
set sampling or time sampling, and hardware monitoring.
Sampling often suffers from either poor accuracy or large
run-time overhead, while hardware measurements have limited
flexibility.
We present DLTune, a prototype tool that performs spatial
and temporal data-locality analysis in run time. It
measures both spatial and temporal locality for the entire
application and individual data structures in a single run,
and effectively exposes poor data locality based on miss
ratio estimates of fully-associative caches. The tool is
based on an elaborate and novel sampling technique that
allows all information to be collected in a single run with
an overall sampling rate as low as one memory reference in
ten million and an average slowdown below five on large
workloads.}
}
@TechReport{ it:2003-056,
author = {Parosh Aziz Abdulla and Johann Deneux and Pritha Mahata
and Aletta Nyl{\'e}n},
title = {Forward Reachability Analysis of Timed Petri Nets},
institution = it,
department = docs,
year = 2003,
number = {2003-056},
month = dec,
abstract = {We consider verification of safety properties for
concurrent real-timed systems modelled by timed Petri nets,
by performing symbolic forward reachability analysis. We
introduce a formalism, called \emph{region generators} for
representing sets of markings of timed Petri nets. Region
generators characterize downward closed sets of regions.
Downward closed languages provide exact abstractions of
sets of reachable states with respect to safety properties.
We show that the standard operations needed for performing
symbolic reachability analysis are computable for region
generators. Since forward reachability analysis is
necessarily incomplete, we introduce an acceleration
technique to make the procedure terminate more often on
practical examples.
We have implemented a prototype for analyzing timed Petri
nets and used it to verify a parameterized version of
Fischer's protocol. We also used the tool to generate a
finite-state abstraction of the protocol.}
}
@TechReport{ it:2003-055,
author = {Martin Nilsson},
title = {Rapid Solution of Parameter-Dependent Linear Systems for
Electromagnetic Problems in the Frequency Domain},
institution = it,
year = 2003,
number = {2003-055},
month = nov,
abstract = {The Minimal Residual Interpolation method reduces the
number of iterations in an iterative method for multiple
right hand sides. It uses computed solutions to initialize
an iterative solver with an accurate guess. This paper
demonstrates the efficiency of the method for frequency
sweeps and solving scattering problems by plane waves
incident from multiple angles. A bound on the number of
solutions required for plane wave scattering before the
remaining solutions are obtained by Minimal Residual
Interpolation only is given. We discuss the performance of
the method compared to iterative seed techniques. In a
numerical example a reduction factor of $60$ is obtained on
the number of matrix vector multiplications.}
}
@TechReport{ it:2003-054,
author = {Martin Nilsson},
title = {Stability of the Fast Multipole Method for {H}elmholtz
Equation in Three Dimensions},
institution = it,
department = tdb,
year = 2003,
number = {2003-054},
month = nov,
abstract = {Stability limits for the diagonal forms approximating the
free space Green's function in Helmholtz' equation are
derived. It is shown that while the original approximation
of the Green's function is stable except for overflows, the
diagonalized form becomes unstable due to errors from
roundoff, interpolation, choice of quadrature rule and
approximation of the translation operator. Numerical
experiments validate the theoretical estimates.}
}
@TechReport{ it:2003-053,
author = {Erik B{\"a}ngtsson and Maya Neytcheva},
title = {Approaches to Reduce the Computational Cost when Solving
Linear Systems of Equations Arising in Boundary Element
Method Discretizations},
institution = it,
department = tdb,
year = 2003,
number = {2003-053},
month = nov,
abstract = {Preconditioned iterative solution methods are compared
with the direct Gaussian elimination method to solve dense
linear systems $A\mathbf{x} = \mathbf{b}$ which originate
from crack propagation problems, modeled and discretized by
boundary element (BEM) techniques.
Numerical experiments are presented and compared with the
direct solution method available in a commercial BEM
package. The experiments show that the preconditioned
iterative schemes are competitive compared to the direct
solver with respect to both arithmetic operations required
and memory demands.}
}
@TechReport{ it:2003-052,
author = {Magnus Sv{\"a}rd and Jan Nordstr{\"o}m},
title = {Well Posed Boundary Conditions for the {N}avier-{S}tokes
Equations},
institution = it,
department = tdb,
year = 2003,
number = {2003-052},
month = nov,
note = {Updated March 2004},
abstract = {In this article we propose a general procedure that allows
us to determine both the number and type of boundary
conditions for time dependent partial differential
equations. With those, well posedness can be proven for a
general initial-boundary value problem. The procedure is
exemplified on the linearised Navier-Stokes equations in
two and three space dimensions on a general domain.}
}
@TechReport{ it:2003-051,
author = {Pavel Krcal and Wang Yi},
title = {Decidable and Undecidable Problems in Schedulability
Analysis Using Timed Automata},
institution = it,
department = docs,
year = 2003,
number = {2003-051},
month = nov,
abstract = {We study schedulability problems of timed systems with
non-uniformly recurring computation tasks. Assume a set of
real time tasks whose best and worst execution times, and
deadlines are known. We use timed automata to describe the
arrival patterns (and release times) of tasks. From the
literature, it is known that the schedulability problem for
a large class of such systems is decidable and can be
checked efficiently.
In this paper, we provide a summary on what is decidable
and what is undecidable in schedulability analysis using
timed automata. Our main technical contribution is that the
schedulability problem will be undecidable if these two
conditions hold: (1) the execution times of tasks are
intervals and (2) a task is allowed to reset clocks. We
show that if one of the above two conditions is dropped,
the problem will be decidable again. Thus our result can be
used as an indication in identifying classes of timed
systems that can be analysed efficiently.}
}
@TechReport{ it:2003-050,
author = {Alexandre David},
title = {Hierarchical Modeling and Analysis of Timed Systems},
institution = it,
department = docs,
year = 2003,
opttype = {PhD thesis},
number = {2003-050},
month = nov,
note = {PhD thesis},
abstract = {\textsc{Uppaal} is a tool for model-checking real-time
systems developed jointly by Uppsala University and Aalborg
University. It has been applied successfully in case
studies ranging from communication protocols to multimedia
applications. The tool is designed to verify systems that
can be modeled as networks of timed automata. But it lacks
support for systems with hierarchical structures, which
makes the construction of large models difficult. In this
thesis we improve the efficiency of \textsc{Uppaal} with
new data structures and extend its modeling language and
its engine to support hierarchical constructs.
To investigate the limits of \textsc{Uppaal}, we model and
analyze an industrial fieldbus communication protocol. To
our knowledge, this case study is the largest application
\textsc{Uppaal} has been confronted to and we managed to
verify the models. However, the hierarchical structure of
the protocol is encoded as a network of automata without
hierarchy, which artificially complicates the model. It
turns out that we need to improve performance and enrich
the modeling language.
To attack the performance bottlenecks, we unify the two
central structures of the \textsc{Uppaal} engine, the
passed and waiting lists, and improve memory management to
take advantage of data sharing between states. We present
experimental results that demonstrate improvements by a
factor 2 in time consumption and a factor 5 in memory
consumption.
We enhance the modeling capabilities of \textsc{Uppaal} by
extending its input language with hierarchical constructs
to structure the models. We have developed a verification
engine that supports modeling of hierarchical systems
without penalty in performance. To further benefit from the
structures of models, we present an approximation technique
that utilizes hierarchy in verification.
Finally, we propose a new architecture to integrate the
different verification techniques into a common framework.
It is designed as a pipeline built with components that are
changed to fit particular experimental configurations and
to add new features. The new engine of \textsc{Uppaal} is
based on this architecture. We believe that the
architecture is applicable to other verification tools.}
}
@TechReport{ it:2003-049,
author = {Martin Nilsson},
title = {A Parallel Shared Memory Implementation of the Fast
Multipole Method for Electromagnetics},
institution = it,
department = tdb,
year = 2003,
number = {2003-049},
month = oct,
abstract = {An implementation of the multilevel Fast Multipole method
for time harmonic electromagnetic computations is
presented. The method is parallelized for shared memory
machines. A new parallelization scheme which is a hybrid
between previous methods is proposed. Several symmetries
and other methods that reduce the storage requirement are
proposed. The most important symmetry is for the
translation operators. A method for reducing the CPU-time
in the interpolation is also proposed.}
}
@TechReport{ it:2003-048,
author = {Timour Katchaounov and Tore Risch},
title = {Interface Capabilities for Query Processing in Peer
Mediator Systems},
institution = it,
department = csd,
year = 2003,
number = {2003-048},
month = sep,
abstract = {A peer mediator system (PMS) is a decentralized mediator
system based on the P2P paradigm, where mediators integrate
data sources and other mediators through views defined in a
multi-mediator query language. In a PMS mediator peers
compose views in terms of views in other peers - mediators
and sources, or directly pose queries in the multi-mediator
query language to some peer. All peers are fully autonomous
and there is no central catalog or controller. Each peer in
a PMS must provide an interface to its data and meta-data
sufficient to allow the cooperative processing of queries
by the PMS. We analyze the computational capabilities and
meta-data that a software system has to export in order to
participate as a peer in a PMS. For the analysis we
identify and compare six classes of peer interfaces with
increasing complexity. For each class we investigate the
performance and scalability implications that result from
the available capabilities and required meta-data. Our
results are two-fold: \emph{i)} we provide guidelines for
the design of mediator peers that can make best use of the
interfaces provided by the data sources, and \emph{ii)} we
analyze the tradeoffs in the design of inter-mediator
interfaces so that mediator peers can efficiently cooperate
to process queries against other composed mediators.
Finally we describe the choices made in a concrete
implementation of a PMS.}
}
@TechReport{ it:2003-047,
author = {Jimmy Flink},
title = {Simuleringsmotor f{\"o}r t{\aa}gtrafik med st{\"o}d
f{\"o}r experimentell konfiguration},
institution = it,
department = hci,
year = 2003,
number = {2003-047},
month = sep,
note = {M.Sc. thesis. In Swedish},
abstract = {A train simulator has been developed using Java and XML.
The purpose is to use it as a tool in the process to build
prototypes of future train driver interfaces. This work has
been done within the LINS project at the division of
human-computer interaction at Uppsala University. The LINS
project aims to investigate issues about the train drivers'
existing and future information environment. Prototypes of
train driver interfaces is to be developed and one of the
tasks is to study the impact of the train driver's
situation awareness compared to the current ATC system and
the upcoming ERTMS/ETCS. }
}
@TechReport{ it:2003-046,
author = {Mathias Spjuth and Martin Karlsson and Erik Hagersten},
title = {The Elbow Cache: A Power-Efficient Alternative to Highly
Associative Caches},
institution = it,
department = docs,
year = 2003,
number = {2003-046},
month = sep,
abstract = {Increasing the associativity is a common way to reduce the
performance-detrimental conflicts in a cache. From a
dynamic cache power perspective this associativity comes at
a high cost. In this paper we present miss ratio
performance and dynamic power estimates for a skewed cache
and also for the organization proposed in this paper, the
elbow cache. We will show that by extending a skewed cache
organization with a relocation strategy we can obtain a
miss ratio that is comparable to the miss ratio of an 8-way
set-associative cache, while consuming up to 48\% less
dynamic power.}
}
@TechReport{ it:2003-045,
author = {Sven-Olof Nystr{\"o}m},
title = {A Polyvariant Type Analysis for {E}rlang},
institution = it,
department = csd,
year = 2003,
number = {2003-045},
month = sep,
abstract = {This paper presents a type analysis for the programming
language Erlang. The analysis computes interprocedural
control-flow and data-flow information, and should be
applicable to any higher-order functional programming
language with call-by-value semantics. The analysis uses a
novel method for polyvariance, \emph{static limiting},
where an approximation of the call graph is analyzed to
determine whether a function should be treated as
polyvariant or monovariant. A general framework for
polyvariant analysis is presented. This framework is used
for experimental investigations to evaluate the cost and
potential benefits of polyvariant analysis and to compare
different approaches to polyvariant analysis. The
experimental results show that static limiting gives the
same or better precision as the other polyvariant analyses,
while having more predictable analysis times. However, the
experiments show only small improvements in precision for
the various polyvariant analyses. }
}
@TechReport{ it:2003-044,
author = {Dan Wallin and Henrik Johansson and Sverker Holmgren},
title = {Cache Memory Behavior of Advanced {PDE} Solvers},
institution = it,
year = 2003,
number = {2003-044},
month = aug,
note = {A short version of this paper will appear in the
proceedings of \emph{Parallel Computing 2003} (ParCo2003),
Dresden, Germany},
abstract = {Three different partial differential equation (PDE) solver
kernels are analyzed in respect to cache memory performance
on a simulated shared memory computer. The kernels
implement state-of-the-art solution algorithms for complex
application problems, and the simulations are performed for
data sets of realistic size.
The performance of the studied applications benefits from
much longer cache lines than normally found in commercially
available computer systems. The reason for this is that
numerical algorithms are carefully coded and have regular
memory access patterns. These programs take advantage of
spatial locality and the amount of false sharing is
limited. A simple sequential hardware prefetch strategy,
providing cache behavior similar to a large cache line,
could potentially yield large performance gains for these
applications. Unfortunately, such prefetchers often lead to
additional address snoops in multiprocessor caches.
However, applying a bundle technique, which lumps several
read address transactions together, this large increase in
address snoops can be avoided. For all studied algorithms,
both the address snoops and cache misses are largely
reduced in the bundled prefetch protocol.}
}
@TechReport{ it:2003-043,
author = {Kajsa Ljungberg and Sverker Holmgren and {\"O}rjan
Carlborg},
title = {Simultaneous Search for Multiple {QTL} Using the Global
Optimization Algorithm {DIRECT}},
institution = it,
department = tdb,
year = 2003,
number = {2003-043},
month = aug,
abstract = {\textbf{Motivation:} Epistatic interactions are important
for quantitative traits. To maximize the power to detect
epistatic quantitative trait loci (QTLs), a simultaneous
search is necessary. The computational complexity demands
that the traditional exhaustive search be replaced by a
more efficient global optimization algorithm.
\textbf{Results:} We have adapted DIRECT, an algorithm
presented in \cite{Jones93}, to the problem of simultaneous
mapping of two and three QTL. We have compared DIRECT, in
terms of accuracy and speed analyzing real data sets, with
standard exhaustive search and a genetic algorithm
previously used for QTL mapping in two dimensions. In all
two- and three-QTL test cases, DIRECT accurately finds the
global optimum two to four orders of magnitude faster than
when using an exhaustive search, and one order of magnitude
faster than when using the genetic algorithm. A search
using a model with three fully interacting QTL is finished
in six CPU minutes when using DIRECT, while an exhaustive
search takes 142 CPU days. Thus three-QTL randomization
testing for determining empirical significance thresholds
is made feasible by the use of DIRECT. This opens the
possibility to thoroughly investigate the power of
simultaneous search to detect at least three interacting
QTL.
\textbf{Availability:} The source code of the prototype
implementation is available at
\url{http://www.tdb.uu.se/~kl/qtl_software.html}.
\textbf{Contact:} kl@tdb.uu.se}
}
@TechReport{ it:2003-042,
author = {Gerardo Schneider},
title = {Invariance Kernels of Polygonal Differential Inclusions},
institution = it,
department = docs,
year = 2003,
number = {2003-042},
month = aug,
note = {Updated October 2003},
abstract = {Polygonal hybrid systems are a subclass of planar hybrid
automata which can be represented by piecewise constant
differential inclusions (SPDIs). Here, we identify and
compute an important object of SPDIs' phase portrait,
namely \emph{invariance kernels}. An \emph{invariant set}
is a set of initial points of trajectories which keep
rotating in a cycle forever and the \emph{invariance
kernel} is the largest of such sets. We show that this
kernel is a non-convex polygon and we give a non-iterative
algorithm for computing the coordinates of its vertices and
edges.}
}
@TechReport{ it:2003-041,
author = {Wendy Kress},
title = {A Compact Fourth Order Time Discretization Method for the
Wave Equation},
institution = it,
department = tdb,
year = 2003,
number = {2003-041},
month = aug,
abstract = {A fourth order accurate discretization in time and space
for the wave equation in first order system formulation is
investigated. The unconditional stability of the scheme is
established and the performance of the scheme is compared
to a second order accurate scheme for a smooth one
dimensional problem and it is also applied to a two
dimensional problem with piecewise constant coefficients.
}
}
@TechReport{ it:2003-040,
author = {Wendy Kress},
title = {Error Estimates for Deferred Correction Methods in Time},
institution = it,
department = tdb,
year = 2003,
number = {2003-040},
month = aug,
abstract = {In this paper, we consider the deferred correction
principle for high order accurate time discretization of
partial differential equations (PDEs) and ordinary
differential equations (ODEs). Deferred correction is based
on a lower order method, here we use second order accurate
A-stable methods. Solutions of higher order accuracy are
computed successively. The computational complexity for
calculating higher order solutions is comparable to the
complexity of the lower order method. There is no stability
restraint on the size of the time-step. Error estimates are
derived and the application of the schemes to initial
boundary value problems is discussed in detail. The
theoretical results are supported by a series of numerical
experiments.}
}
@TechReport{ it:2003-039,
author = {Therese Berg and Bengt Jonsson and Martin Leucker and
Mayank Saksena},
title = {Insights to Angluin's Learning},
institution = it,
department = docs,
year = 2003,
number = {2003-039},
month = aug,
abstract = {Among other domains, learning finite-state machines is
important for obtaining a model of a system under
development, so that powerful formal methods such as model
checking can be applied.
A prominent algorithm for learning such devices was
developed by Angluin. We have implemented this algorithm in
a straightforward way to gain further insights to practical
applicability. Furthermore, we have analyzed its
performance on randomly generated as well as real-world
examples. Our experiments focus on the impact of the
alphabet size and the number of states on the needed number
of membership queries. Additionally, we have implemented
and analyzed an optimized version for learning
prefix-closed regular languages. Memory consumption is one
major obstacle when we attempted to learn large examples.
We see that prefix-closed languages are relatively hard to
learn compared to arbitrary regular languages. The
optimization, however, shows positive results. }
}
@TechReport{ it:2003-038,
author = {Henrik Bj{\"o}rklund and Sven Sandberg and Sergei
Vorobyov},
title = {On Fixed-Parameter Complexity of Infinite Games},
institution = it,
department = csd,
year = 2003,
number = {2003-038},
month = aug,
abstract = {We investigate and classify fixed parameter complexity of
several infinite duration games, including Rabin, Streett,
Muller, parity, mean payoff, and simple stochastic, using
different natural parameterizations.
Most known fixed parameter intractable games are PSPACE- or
EXP-complete classically, AW[*] or XP-hard parametrically,
and are all finite duration games. In contrast, the games
we consider are infinite duration, solvable in positional
or finite memory strategies, and belong to ``lower''
complexity classes, like NP and/or coNP. However, the best
known algorithms they possess are of complexity $n^{f(k)}$,
i.e., XP is the only upper bound, with no known parametric
lower bounds.
We demonstrate that under different parameterizations these
games may have different or equivalent FPT-statuses, and
present several tractable and intractable cases.}
}
@TechReport{ it:2003-037,
author = {Dan Wallin and Erik Hagersten},
title = {Bundling: Reducing the Overhead of Multiprocessor
Prefetchers},
institution = it,
department = docs,
year = 2003,
number = {2003-037},
month = aug,
abstract = {Prefetching has proven useful for reducing cache misses in
multiprocessors at the cost of increased coherence traffic.
This is especially troublesome for snooping-based systems,
where the available coherence bandwidth often is the
scalability bottleneck.
The new bundling technique, introduced in this paper,
reduces the overhead caused by prefetching by two means:
piggybacking prefetches with normal requests; and,
requiring only one device on the ``bus'' to perform a snoop
lookup for each prefetch transaction. This paper describes
bundling implementations for three important transaction
types: reads, upgrades and downgrades.
While bundling could reduce the overhead of most existing
prefetch schemes, the evaluation of bundling performed in
this paper has been limited to two of them: sequential
prefetching and Dahlgren's adaptive sequential prefetching.
Both schemes have their snoop bandwidth cut in about half
for all the commercial and scientific benchmarks studied.
The combined effect of bundling applied to these fairly
naive prefetch schemes lowers the cache miss rate, the
address bandwidth, as well as the snoop bandwidth compared
with no prefetching for all applications - a result never
demonstrated before.
Bundling, however, will not reduce the data bandwidth
introduced by a prefetch scheme. We argue, however, that
the data bandwidth is more easily scaled than the snoop
bandwidth for snoop-based coherence systems.}
}
@TechReport{ it:2003-036,
author = {Emad Abd-Elrady and Torsten S{\"o}derstr{\"o}m and
Torbj{\"o}rn Wigren},
title = {Periodic Signal Modeling Based on Li{\'e}nard's Equation},
institution = it,
department = syscon,
year = 2003,
number = {2003-036},
month = aug,
abstract = {The problem of modeling periodic signals is considered.
The approach taken here is motivated by the well known
theoretical results on the existence of periodic orbits for
Li{\'e}nard systems and previous results on modeling
periodic signals by means of second order nonlinear
ordinary differential equations (ODEs). The approach makes
use of the appropriate conditions imposed on the
polynomials of a Li{\'e}nard system to guarantee the
existence of a unique and stable limit cycle. These
conditions reduce the number of parameters required to
generate accurate models for periodic signals.}
}
@TechReport{ it:2003-035,
author = {Elisabeth Larsson and Bengt Fornberg},
title = {Theoretical and Computational Aspects of Multivariate
Interpolation with Increasingly Flat Radial Basis
Functions},
institution = it,
department = tdb,
year = 2003,
number = {2003-035},
month = jun,
abstract = {Multivariate interpolation of smooth data using smooth
radial basis functions is considered. The behavior of the
interpolants in the limit of nearly flat radial basis
functions is studied both theoretically and numerically.
Explicit criteria for different types of limits are given.
Using the results for the limits, the dependence of the
error on the shape parameter of the radial basis function
is investigated. The mechanisms that determine the optimal
shape parameter value are studied and explained through
approximate expansions of the interpolation error.}
}
@TechReport{ it:2003-034,
author = {Per L{\"o}tstedt and Alison Ramage and von Sydow, Lina and
Stefan S{\"o}derberg},
title = {Preconditioned Implicit Solution of Linear Hyperbolic
Equations with Adaptivity},
institution = it,
department = tdb,
year = 2003,
number = {2003-034},
month = may,
abstract = {This paper describes a method for solving hyperbolic
partial differential equations using an adaptive grid: the
spatial derivatives are discretised with a finite volume
method on a grid which is structured and partitioned into
blocks which may be refined and derefined as the solution
evolves. The solution is advanced in time via a backward
differentiation formula. The discretisation used is second
order accurate and stable on Cartesian grids. The resulting
system of linear equations is solved by GMRES at every
time-step with the convergence of the iteration being
accelerated by a semi-Toeplitz preconditioner. The
efficiency of this preconditioning technique is analysed
and numerical experiments are presented which illustrate
the behaviour of the method on a parallel computer. }
}
@TechReport{ it:2003-033,
author = {Daniel Noreland},
title = {A Gradient Based Optimisation Algorithm for the Design of
Brass-Wind Instruments},
institution = it,
department = tdb,
year = 2003,
number = {2003-033},
month = may,
abstract = {This paper presents how the shape of a brass instrument
can be optimised with respect to its intonation and
impedance peak magnitudes. The instrument is modelled using
a one-dimensional transmission line analogy with truncated
cones. The optimisation employs the Levenberg-Marquardt
method, with the gradient of the objective function
obtained by analytic manipulation. Through the use of an
appropriate choice of design variables, the optimisation is
capable of rapidly finding smooth horn profiles.}
}
@TechReport{ it:2003-032,
author = {Daniel Noreland},
title = {Impedance Boundary Conditions for Acoustic Waves in a Duct
with a Step Discontinuity},
institution = it,
department = tdb,
year = 2003,
number = {2003-032},
month = may,
abstract = {This paper treats the use of numerically computed
impedance boundary conditions for acoustic simulations.
Such boundary conditions may be used to combine different
methods on different parts of the computational domain.
Impedance boundary conditions may be computed for each
subproblem independently of each other. In order to develop
insight into this approach, wave propagation in a
rectangular waveguide with a step discontinuity is
studied.}
}
@TechReport{ it:2003-031,
author = {Daniel Noreland},
title = {Ill-Posedness of Absorbing Boundary Conditions Applied on
Convex Surfaces},
institution = it,
department = tdb,
year = 2003,
number = {2003-031},
month = may,
abstract = {Absorbing boundary conditions are important in many
applications where partial differential equations defined
on infinite domains are solved numerically. A problem that
has attracted interest recently is that perfectly matched
layers layers (PML) for electro-magnetic FDTD simulations
applied on convex surfaces may lead to instabilities. This
paper shows that these problems are not restricted to
electro-magnetic calculations, but common for problems
described by the classical wave equation with absorbing
boundary conditions on convex surfaces. It is shown that
the instabilities are independent of the numerical
implementation of the absorbing boundary condition, and
instead a result of unphysical assumption in the
formulation of the boundary condition. }
}
@TechReport{ it:2003-030,
author = {M. Ekman and P. Samuelsson and B. Carlsson},
title = {Adaptive Control of the Nitrate Level in an Activated
Sludge Process Using an External Carbon Source - Extended
Version},
institution = it,
department = syscon,
year = 2003,
number = {2003-030},
month = may,
note = {A shorter version is also available in: Preprints of
Reglerm{\"o}te 2002, Link{\"o}ping, Sweden, May 29--30
2002, pp 308--313, and another version in: Proc. of the 1st
World Water Congress of the IWA. Melbourne, 2002 (poster
presentation). Updated July 2003},
abstract = {In an activated sludge process for nitrogen removal,
nitrate may be reduced to nitrogen gas by facultative
heterotrophic bacteria in an anoxic environment. In order
to guarantee sufficient supplies of readily biodegradable
carbon compounds, an external carbon source often needs to
be added. In this report, we present an automatic control
strategy for controlling the nitrate level using an
external carbon source. The external carbon source is added
in the first anoxic compartment and the nitrate
concentration in the last anoxic compartment is controlled.
Key process parameters of a simplified Activated Sludge
Model No. 1 are estimated on-line. The estimated parameters
are used for updating the parameters of a linear quadratic
controller. The strategy is illustrated in a simulation
study using realistic influent data and is shown to perform
well.}
}
@TechReport{ it:2003-029,
author = {Oskar Grenholm and Zoran Radovic and Erik Hagersten},
title = {Latency-hiding and Optimizations of the {DSZOOM}
Instrumentation System},
institution = it,
department = docs,
year = 2003,
number = {2003-029},
month = may,
abstract = {An efficient and robust instrumentation tool (or compiler
support) is necessary for an efficient implementation of
fine-grain software-based shared memory systems (SW-DSMs).
The DSZOOM system, developed by the Uppsala Architecture
Research Team (UART) at Uppsala University, is a
sequentially consistent fine-grained SW-DSM originally
developed using Executable Editing Library (EEL)---a binary
modification tool from University of Wisconsin-Madison. In
this paper, we identify several weaknesses of this original
approach and present a new and simple tool for assembler
instrumentation: Sparc Assembler Instrumentation Tool
(SAIT). This tool can instrument (modify) a highly
optimized assembler output from the compiler for the newest
UltraSPARC processors. Currently, the focus of the tool is
load-, store-, and load-store-instrumentation.
By using the SAIT, we develop and present several low-level
instrumentation optimization techniques that significantly
improve the performance of the original DSZOOM system. One
of the presented techniques is a write permission cache
(WPC), a latency-hiding mechanism for memory-store
operations, that can lower the instrumentation overheads
for some applications (as much as 45\% for LU-cont, running
on two nodes with 8 processors each).
Finally, we demonstrate that this new DSZOOM system
executes faster than the old one for all 13 applications
studied, from the SPLASH-2 benchmark suite. Execution time
improvement factors range from 1.07 to 2.82 (average 1.73).
}
}
@TechReport{ it:2003-028,
author = {Erik K. Larsson},
title = {Limiting Properties of Sampled Stochastic Systems},
institution = it,
department = syscon,
year = 2003,
number = {2003-028},
month = may,
abstract = {The objective of this paper is to present some general
properties of discrete-time systems originating from fast
sampled continuous-time stochastic systems. In particular,
some results concerning the zero locations and the
innovations variance of fast sampled continuous-time
autoregressive moving average (ARMA) systems will be
stated. Knowledge of these properties is of importance and
interest in various fast sampling applications, such as
discrete-time simulation of continuous-time systems and
identification of continuous-time systems using
discrete-time measurements. The main contribution, however,
is to provide some insight into questions like: when can
simple approximate sampling schemes be applied accurately
enough and what determines the characteristic dynamic of a
fast sampled system. The results are illustrated by an
extensive set of examples. }
}
@TechReport{ it:2003-027,
author = {Per Carlsson and Arne Andersson and Fredrik Ygge},
title = {A Tractable Mechanism for Time Dependent Markets},
institution = it,
department = csd,
year = 2003,
number = {2003-027},
month = apr,
note = {Updated October 2004 with new complexity results},
abstract = {Markets with time dependent goods are special cases of
multi commodity markets. An application area of high
interest is day-ahead power markets. If these are to be
opened for consumer side bidders and local production
bidders, the number of actors on the market grows
dramatically, and new market mechanisms and algorithms are
needed. Another interesting application area with many
similarities is bandwidth markets.
The design of large flexible markets with time dependent
goods is a computational challenge. In this paper we
present a computationally tractable mechanism for time
dependent markets. By a number of predefined bid types, it
offers useful flexibility to the bidders. We present the
market mechanism and the corresponding matching algorithm
together with some analysis of its behaviour.}
}
@TechReport{ it:2003-026,
author = {Henrik L{\"o}f and Zoran Radovic and Erik Hagersten},
title = {{THROOM} --- Running {POSIX} Multithreaded Binaries on a
Cluster},
institution = it,
department = docs,
year = 2003,
number = {2003-026},
month = apr,
abstract = {Most software distributed shared memory systems (SW-DSMs)
lack industry standard interfaces that limit their
applicability to a small set of shared-memory applications.
In order to gain general acceptance, SW-DSMs should support
the same look-and-feel of shared memory as hardware DSMs.
This paper presents a runtime system concept that enables
unmodified POSIX P1003.1c (Pthreads) compliant binaries to
run transparently on clustered hardware. The key idea is to
extend the single process model of multi-threading to a
multi-process model where threads are distributed to
processes executing in remote nodes. The distributed
threads execute in a global shared address space made
coherent by a fine-grain SW-DSM layer. We also present
THROOM, a proof-of-concept implementation that runs
unmodified Pthread binaries on a virtual cluster modeled as
standard UNIX processes. THROOM runs on top of the DSZOOM
fine-grain SW-DSM system with limited OS support.}
}
@TechReport{ it:2003-025,
author = {Torbj{\"o}rn Wigren and Torsten S{\"o}derstr{\"o}m},
title = {Second Order {ODE}s are Sufficient for Modeling of Many
Periodic Signals},
institution = it,
department = syscon,
year = 2003,
number = {2003-025},
month = apr,
abstract = {Which is the minimum order an autonomous nonlinear
ordinary differential equation (ODE) needs to have to be
able to model a periodic signal? This question is motivated
by recent research on periodic signal analysis, where
nonlinear ODEs are used as models. The results presented
here show that an order of two of the ODE is sufficient for
a large class of periodic signals. More precisely,
conditions on a periodic signal are established that imply
the existence of an ODE that has the periodic signal as a
solution. A criterion that characterizes the above class of
periodic signals by means of the overtone contents of the
signals is also presented. The reason why higher order ODEs
are sometimes needed is illustrated with geometric
arguments. Extensions of the theoretical analysis to cases
with orders higher than two are developed using this
insight.}
}
@TechReport{ it:2003-024,
author = {Parosh Aziz Abdulla and Bengt Jonsson and Marcus Nilsson
and Julien d'Orso},
title = {Algorithmic Improvements in Regular Model Checking},
institution = it,
department = docs,
year = 2003,
number = {2003-024},
month = apr,
note = {Extended version of paper accepted for publication in in
CAV'2003},
abstract = {Regular model checking is a form of symbolic model
checking for parameterized and infinite-state systems,
whose states can be represented as finite strings of
arbitrary length over a finite alphabet, in which regular
sets of words are used to represent sets of states. In
earlier papers, we have developed methods for computing the
transitive closure (or the set of reachable states) of the
transition relation, represented by a regular
length-preserving transducer. In this paper, we present
several improvements of these techniques, which reduce the
size of intermediate approximations of the transitive
closure: One improvement is to pre-process the transducer
by {\em bi-determinization}, another is to use a more
powerful equivalence relation for identifying histories
(columns) of states in the transitive closure. We also
present a simplified theoretical framework for showing
soundness of the optimization, which is based on commuting
simulations. The techniques have been implemented, and we
report the speedups obtained from the respective
optimizations.}
}
@TechReport{ it:2003-023,
author = {Bertil Gustafsson and Per Wahlund},
title = {Time Compact Difference Methods for Wave Propagation in
Discontinuous Media},
institution = it,
department = tdb,
year = 2003,
number = {2003-023},
month = apr,
abstract = {In an earlier paper by Gustafsson and Mossberg, a fourth
order one-step method was constructed for the solution of
wave propagation problems. The method is based on the first
order system form of the PDE, and uses a staggered grid
both in space and time. The method was also applied with
good results to a problem with discontinuous coefficients
without using any special procedure across the
discontinuity. In this paper we will analyze a model
problem from acoustics, and demonstrate the theoretical
foundation for this behavior. Furthermore, we shall present
more detailed numerical experiments which confirm the
theoretical results.}
}
@TechReport{ it:2003-022,
author = {Bharath Bhikkaji and Kaushik Mahata and Torsten
S{\"o}derstr{\"o}m},
title = {Reduced order models for a two-dimensional heat diffusion
system},
institution = it,
department = syscon,
year = 2003,
number = {2003-022},
month = apr,
abstract = {In this paper, a two-dimensional heat diffusion system,
which is modeled by a partial differential equation (PDE)
is considered. Finite order approximations, for the
infinite order PDE model, are constructed first by a direct
application of the standard finite difference approximation
(FD) scheme. Using tools of linear algebra, the constructed
FD approximate models are reduced to computationally
simpler models without any loss of accuracy. Further, the
reduced approximate models are modified by replacing its
poles with their respective asymptotic limits. Numerical
experiments suggest that the proposed modifications improve
the accuracy of the approximate models.}
}
@TechReport{ it:2003-021,
author = {Christian Tschudin and Richard Gold},
title = {LUNAR: Lightweight Underlay Network Ad-hoc Routing},
institution = it,
department = docs,
year = 2003,
number = {2003-021},
month = apr,
note = {Originally written January 2002; updated April 2002},
abstract = {In this paper we present an new ad hoc routing system
based upon simple principles regarding the routing strategy
and the implementation approach. In the routing area we
(re-)introduce the end-to-end principle, letting the
communicating end nodes make the decisions concerning the
behaviour of intermediate nodes. We adopt a routing
strategy that is a mixture of on-demand and pro-active
routing in order to minimize the possible down-times of
communication paths. Implementation-wise we use explicit
``resolution commands'' sent to neighbour nodes to provide
LUNAR functionality. A freely available implementation has
been produced that includes auto-configuration of IP
network addresses and default gateway routing, making LUNAR
a fully self-configuring ad-hoc routing solution which
supports both unicast and broadcast styles of
communication.}
}
@TechReport{ it:2003-020,
author = {Christian Tschudin and Richard Gold},
title = {SelNet: A Translating Underlay Network},
institution = it,
department = docs,
year = 2003,
number = {2003-020},
month = apr,
note = {Originally written October 2001},
abstract = {The Internet has successfully promoted address uniformity
and a node centric forwarding semantics. However, NAT and
wireless networks among others have shown the advantage and
the need of revising basic assumptions of the Internet
model. In this paper we review several of these basic
networking concepts and introduce a new set of network
abstractions like ``membranes'' which are individual
physical or virtual networks and ``wormholes'' which link
one or more membranes together. This leads us to an active
network architecture called SelNet that is based on
tunnelling and translation mechanisms. Besides the
architecture we present several network services and
abstractions that can be built on top of it. A brief status
report on a prototype implementation is also provided.}
}
@TechReport{ it:2003-019,
author = {Henrik Bj{\"o}rklund and Sven Sandberg and Sergei
Vorobyov},
title = {Randomized Subexponential Algorithms for Parity Games},
institution = it,
department = csd,
year = 2003,
number = {2003-019},
month = apr,
abstract = {The complexity of solving parity games is an important
open problem in verification, automata theory, and
complexity theory. In this paper we develop an abstract
setting for studying parity games and related problems,
based on function optimization over certain discrete
structures. We introduce new classes of \emph{completely
local-global (CLG)} and \emph{recursively local-global
(RLG)} functions, and show that strategy evaluation
functions for parity games belong to these classes. We also
establish a relation to the previously well-studied
\emph{completely unimodal (CU)} and \emph{local-global}
functions. A number of nice properties of CLG-functions are
proved.
In this setting, we survey several randomized optimization
algorithms appropriate for CU-, CLG-, and RLG-functions. We
show that the subexponential algorithms for linear
programming by Kalai and Matou\v{s}ek, Sharir, and Welzl,
can be adapted to optimizing the functions we study, with
preserved subexponential expected running time. We examine
the relations to two other abstract frameworks for
subexponential optimization, the LP-type problems of
Matou{\v{s}}ek, Sharir, and Welzl, and the abstract
optimization problems of G{\"a}rtner. The applicability of
our abstract optimization approach to parity games builds
upon a discrete strategy evaluation measure.
We also consider local search type algorithms, and settle
two nontrivial, but still exponential, upper bounds. As
applications we address some complexity-theoretic issues
including non-PLS-completeness of the problems studied.}
}
@TechReport{ it:2003-018,
author = {Magnus Sv{\"a}rd and Ken Mattsson and Jan Nordstr{\"o}m},
title = {Steady State Computations Using Summation-by-Parts
Operators},
institution = it,
department = tdb,
year = 2003,
number = {2003-018},
month = mar,
abstract = {This paper concerns energy stability on curvilinear grids
and its impact on steady state calulations. We have done
computations for the Euler equations using both high order
summation-by-parts block and diagonal norm schemes. The
calculations indicate the significance of energy stability
in order to obtain convergence to steady state.
Furthermore, the difference operators are improved such
that faster convergence to steady state are obtained. The
numerical experiments also reveal the importance of high
quality grids when high order finite difference methods are
used. }
}
@TechReport{ it:2003-017,
author = {Henrik Bj{\"o}rklund and Sven Sandberg and Sergei
Vorobyov},
title = {An Improved Subexponential Algorithm for Parity Games},
institution = it,
department = csd,
year = 2003,
number = {2003-017},
month = mar,
abstract = {We suggest a new algorithm for deciding parity games, a
fundamental problem of unknown complexity (in \textsc{NP}
$\cap$ \textsc{coNP}, not known to belong to \textsc{P}) in
game, automata, complexity theories, combinatorial
optimization, temporal logic of programs, computer-aided
verification. The novelty of the algorithm consists in
exploiting a special form of parity games with
\emph{retreats}, where optimal retreat edges define
\emph{absorbing facets} (with better values than their
neighbors on complementary facets) in the strategy space. A
superset of such absorbing facets can be found by standard
random iterative improvement algorithms in expected
polynomial time. Additional dual techniques are used to
minimize this superset. As a result, the dimension of the
problem shrinks, to which we finally apply the
Kalai-Matou\v{s}ek-Sharir-Welzl-Ludwig-style randomization
techniques we recently adapted for games [Bjorklund,
Sandberg, Vorobyov, STACS'2003 and TR-2003-002] }
}
@TechReport{ it:2003-016,
author = {Bertil Gustafsson and Eva Mossberg},
title = {Time Compact High Order Difference Methods for Wave
Propagation},
institution = it,
department = tdb,
year = 2003,
number = {2003-016},
month = mar,
abstract = {We construct one-step explicit difference methods for
solution of wave propagation problems with fourth order
accuracy in both space and time by using a principle that
can be generalized to arbitrary order. We use the first
order system form and a staggered grid. The fourth order
accuracy in time is obtained by transferring time
derivatives in the truncation error to space derivatives.
Discontinuous coefficients corresponding to interfaces
between different materials are considered as a special
case of variable coefficients, and the method is applied
across the discontinuities. The accuracy is much improved
compared to second order methods even for this type of
problems. A certain norm is shown to be conserved, ensuring
good accuracy even for long time integration.}
}
@TechReport{ it:2003-015,
author = {Henrik Bj{\"o}rklund and Sven Sandberg},
title = {Algorithms for Combinatorial Optimization and Games
Adapted from Linear Programming},
institution = it,
department = csd,
year = 2003,
number = {2003-015},
month = mar,
abstract = {The problem of maximizing functions from the boolean
hypercube to real numbers arises naturally in a wide range
of applications. This paper studies an even more general
setting, in which the function to maximize is defined on
what we call a hyperstructure. A hyperstructure is the
Cartesian product of finite sets with possibly more than
two elements. We also relax the codomain to any partially
ordered set. Well-behaved such functions arise in game
theoretic contexts, in particular from parity games
(equivalent to the modal mu-calculus model checking) and
simple stochastic games (Bj{\"o}rklund, Sandberg, Vorobyov
2003). We show how several subexponential algorithms for
linear programming (Kalai 1992, Matousek, Sharir, Welzl
1992) can be adapted to hyperstructures and give a
reduction to the abstract optimization problems introduced
in (G{\"a}rtner1995).}
}
@TechReport{ it:2003-014,
author = {Brahim Hnich and Julian Richardson and Pierre Flener},
title = {Towards Automatic Generation and Evaluation of Implied
Constraints},
institution = it,
department = csd,
year = 2003,
number = {2003-014},
month = mar,
abstract = {Adding appropriate implied constraints can dramatically
improve the computational behaviour of a constraint solver
on the augmented set of constraints. We briefly document
experiments we made with PRESS and clp(q,r) for generating
implied constraints.
This report is an excerpt (namely Sections 5.1, 5.2, and
5.3, which are included verbatim apart from minor cosmetic,
non-technical corrections) from an unfinished technical
report written in August 2000, and thus (finally) provides
a citable, published reference to that work.}
}
@TechReport{ it:2003-013,
author = {Ken Mattsson and Magnus Sv{\"a}rd and Jan Nordstr{\"o}m},
title = {Stable Artificial Dissipation Operators for High Order
Finite Difference Schemes},
institution = it,
department = tdb,
year = 2003,
number = {2003-013},
month = feb,
abstract = {Stability for nonlinear convection problems using centered
difference schemes require the addition of artificial
dissipation. In this paper we present dissipation operators
that preserve both stability and accuracy for high order
finite difference approximations of initial boundary value
problems.}
}
@TechReport{ it:2003-012,
author = {Ken Mattsson and Jan Nordstr{\"o}m},
title = {Finite Difference Approximations of Second Derivatives on
Summation by Parts Form},
institution = it,
department = tdb,
year = 2003,
number = {2003-012},
month = feb,
note = {Updated 2003-03-21},
abstract = {Finite difference approximations of second derivatives,
which satisfy a summation by parts rule have been derived
for the 4th, 6th and 8th order case, by using the symbolic
mathematics software Maple. The operators are based on the
same norms as the corresponding approximations of the first
derivate, which make the construction of stable
approximations to general parabolic problems
straightforward. The error analysis show that the second
derivative approximation can be closed at the boundaries
with an approximation two orders less accurate than the
internal scheme, and still preserve the internal accuracy.
However, if an energy estimate cannot be obtained, the
overall convergence rate is reduced by one order. }
}
@TechReport{ it:2003-011,
author = {Alexandre David and Gerd Behrmann and Kim G. Larsen and
Wang Yi},
title = {A Tool Architecture for the Next Generation of UPPAAL},
institution = it,
department = docs,
year = 2003,
number = {2003-011},
month = feb,
abstract = {We present the design of the model-checking engine and
internal data structures for the next generation of UPPAAL.
The design is based on a pipeline architecture where each
stage represents one independent operation in the
verification algorithms. The architecture is based on
essentially one shared data structure to reduce redundant
computations in state exploration, which unifies the
so-called passed and waiting lists of the traditional
reachability algorithm. In the implementation, instead of
using standard memory management functions from
general-purpose operating systems, we have developed a
special-purpose storage manager to best utilize sharing in
physical storage. We present experimental results
supporting these design decisions. It is demonstrated that
the new design and implementation improves the efficiency
of the current distributed version of UPPAAL by about 60\%
in time and 80\% in space.}
}
@TechReport{ it:2003-010,
author = {Alexandre David and Johann Deneux and Julien d'Orso},
title = {A Formal Semantics for {UML} Statecharts},
institution = it,
department = docs,
year = 2003,
number = {2003-010},
month = feb,
abstract = {The UML language is a large set of notations and rules to
describe different aspects of a system. It provides a set
of diagrams to view the system from different angles: use
case diagrams, class diagrams, statecharts diagrams, and
deployment diagrams are some of them. In this report we are
interested in the statecharts diagrams that describe
dynamic behaviours. We give a formal semantics for a large
subset of these statecharts, in particular we focus on the
action language semantics. Our subset and semantics are
very close to the one supported by the tool Rhapsody.}
}
@TechReport{ it:2003-009,
author = {Alexandre David and M. Oliver M{\"o}ller and Wang Yi},
title = {Verification of {UML} Statecharts with Real-Time
Extensions},
institution = it,
department = docs,
year = 2003,
number = {2003-009},
month = feb,
abstract = {We develop a formal model for hierarchical timed systems.
The statechart-like hierarchy features parallelism on any
level and connects superstate and substate via explicit
entries and exits. Time is represented by clocks,
invariants, and guards. For this formalism we give an
operational semantics that is appropriate for the
verification of universal timed computation tree logic
(TCTL) properties.
Our model is strongly related to the timed automata dialect
as present in the model checking tool UPPAAL. Here networks
of timed automata are enriched with shared variables,
hand-shake synchronization, and urgency.
We describe a flattening procedure that translates our
formalism into a network of UPPAAL timed automata. This
flattening preserves a correspondence of the sets of legal
traces. Therefor the translation can be used to establish
properties in the hierarchical model.
As a case study, we use the standard UML modeling example
of a cardiac pacemaker. We model it in our hierarchical
language, flatten it to UPPAAL input, and use the latter
for a formal analysis.
Our formalism remains decidable with respect to TCTL
properties. In general the encoding of statecharts requires
an abstraction step, which is not covered by this article.
}
}
@TechReport{ it:2003-008,
author = {Julian Richardson and Pierre Flener},
title = {Program Schemas as Proof Methods},
institution = it,
department = csd,
year = 2003,
number = {2003-008},
month = feb,
abstract = {Automatic proof and automatic programming have always
enjoyed a close relationship. We present a unification of
proof planning (a knowledge-based approach to automated
proof) and schema-guided synthesis (a knowledge-based
approach to automatic programming). This unification
enhances schema-guided synthesis with features of proof
planning, such as the use of heuristics and the separation
between object-level and meta-level reasoning. It enhances
proof planning with features of schema-guided synthesis,
such as reuse. It allows program schemas and heuristics to
be implemented as proof planning methods. We aim
particularly at implementation within the lambda-Clam proof
planner, whose higher-order features are particularly
appropriate for synthesis. Program synthesis and
satisfaction of its proof obligations, such as verification
conditions, matchings, or simplifications, are thus neatly
integrated.}
}
@TechReport{ it:2003-007,
author = {Henrik Brand{\'e}n and Sverker Holmgren and Per Sundqvist},
title = {Discrete Fundamental Solution Preconditioning for
Hyperbolic Systems of {PDE}},
institution = it,
department = tdb,
year = 2003,
number = {2003-007},
month = feb,
abstract = {We present a new preconditioner for the iterative solution
of linear systems of equations arising from discretizations
of systems of first order partial differential equations
(PDEs) on structured grids. Such systems occur in many
important applications, including compressible fluid flow
and electormagnetic wave propagation. The preconditioner is
a truncated convolution operator, with a kernel that is a
fundamental solution of a difference operator closely
related to the original discretization.
Analysis of a relevant scalar model problem in two spatial
dimensions shows that grid independent convergence is
obtained using a simple one-stage iterative method. As an
example of a more involved problem, we consider the steady
state solution of the non-linear Euler equations in a two
dimensional, non-axisymmetric duct. We present results from
numerical experiments, verifying that the preconditioning
technique again achieves grid independent convergence, both
for an upwind discretization and for a centered second
order discretization with fourth order artificial
viscosity. }
}
@TechReport{ it:2003-006,
author = {Henrik Brand{\'e}n and Per Sundqvist},
title = {An Algorithm for Computing Fundamental Solutions of
Difference Operators},
institution = it,
department = tdb,
year = 2003,
number = {2003-006},
month = feb,
abstract = {We propose an FFT-based algorithm for computing
fundamental solutions of difference operators with constant
coefficients. Our main contribution is to handle cases
where the symbol has zeros.}
}
@TechReport{ it:2003-005,
author = {Samuel Sundberg},
title = {Solving the linearized Navier-Stokes equations using
semi-Toeplitz preconditioning},
institution = it,
department = tdb,
year = 2003,
number = {2003-005},
month = feb,
abstract = {A semi-Toeplitz preconditioner for the linearized
Navier--Stokes equation for compressible flow is proposed
and tested. The preconditioner is applied to the linear
system of equations to be solved in each time step of an
implicit method. The equations are solved with flat plate
boundary conditions and are linearized around the Blasius
solution. The grids are stretched in the normal direction
to the plate and the quotient between the time step and the
space step is varied. The preconditioner works well in all
tested cases and outperforms the method without
preconditioning both in number of iterations and execution
time.}
}
@TechReport{ it:2003-004,
author = {Kaushik Mahata and Torsten S{\"o}derstr{\"o}m},
title = {Subspace estimation of real-valued sine wave frequencies},
institution = it,
department = syscon,
year = 2003,
number = {2003-004},
month = jan,
abstract = {Subspace based estimation of multiple real-valued sine
wave frequencies is considered in this paper. A novel data
covariance model is proposed. In the proposed model the
dimension of the signal subspace equals the number of
frequencies present in the data, which is half of the
signal subspace dimension for the conventional model.
Consequently, an ESPRIT like algorithm using the proposed
data model is presented. The proposed algorithm is then
extended for the case of complex-valued sine waves.
Performance analysis of the proposed algorithms are also
carried out. The algorithms are tested in numerical
simulations. The newly proposed algorithm outperforms
ESPRIT by a significant margin and is computationally
efficient as well. }
}
@TechReport{ it:2003-003,
author = {Magnus Sv{\"a}rd and Jan Nordstr{\"o}m},
title = {A Stable and Accurate Summation-by-Parts Finite Volume
Formulation of the Laplacian Operator},
institution = it,
department = tdb,
year = 2003,
number = {2003-003},
month = jan,
abstract = {Our objective is to analyse a commonly used edge based
finite volume approximation of the Laplacian and construct
an accurate and stable way to implement boundary
conditions. Of particular interest are general unstructured
grids where the strength of the finite volume method is
fully utilised.
As a model problem we consider the heat equation. We
analyse the Cauchy problem in one and several space
dimensions and we prove stability on unstructured grids.
Next, the initial-boundary value problem is considered and
a scheme is constructed in a summation-by-parts framework.
The boundary conditions are imposed in a stable and
accurate manner, using a penalty formulation.
Numerical computations of the wave equation in
two-dimensions are performed, verifying stability and order
of accuracy for structured grids. However, the results are
not satisfying for unstructured grids. Further
investigation reveals that the approximation is not
consistent for general unstructured grids. However, grids
consisting of equilateral polygons recover the convergence.
}
}
@TechReport{ it:2003-002,
author = {Henrik Bj{\"o}rklund and Sven Sandberg and Sergei
Vorobyov},
title = {On Combinatorial Structure and Algorithms for Parity
Games},
institution = it,
department = csd,
year = 2003,
number = {2003-002},
month = jan,
abstract = {In this paper we identify and systematically explore the
combinatorial structure underlying parity and simple
stochastic games. We introduce the class of Completely LG
(local-global) functions with nice structural properties
pertinent to games and allowing for efficient optimization
by iterative improvement local search style algorithms. We
demonstrate several important combinatorial properties of
Completely LG functions, allowing for many optimization
algorithms, and establish a relation with the subclass of
Completely Unimodal functions, studied by Hammer et al.
[1988] Williamson Hoke [1988], and Wiedemann [1985]. We
also describe a new, compared to our recent [STACS'2003],
subexponential randomized algorithm for CU-functions,
CLG-functions, parity, and simple stochastic games, and
establish a relation with the class of LP-type problems
introduced and investigated by Sharir \& Welzl [1992] and
Matousek, Sharir \& Welzl [1992]. }
}
@TechReport{ it:2003-001,
author = {Parosh Abdulla and Johann Deneux and Pritha Mahata and
Aletta Nyl{\'e}n},
title = {Downward Closed Language Generators},
institution = it,
department = docs,
year = 2003,
number = {2003-001},
month = jan,
abstract = {We use downward closed languages for representing sets of
states when performing forward reachability analysis on
infinite-state systems. Downward closed languages are often
more succinct than exact representations of the set of
reachable states. We introduce a formalism for representing
downward closed languages, called \emph{downward closed
language generators (dlgs)}. We show that standard set
operations needed for performing symbolic reachability
analysis are computable for dlgs. Using a class of
hierarchically defined dlgs, we have implemented a
prototype for analysing timed Petri nets and used it to
analyze a parameterized version of Fischer's protocol. We
also show how dlgs can be used for uniform representation
of formalisms previously presented for models such as Petri
nets and lossy channel systems. }
}
@TechReport{ it:2002-041,
author = {Per L{\"o}tstedt and Martin Nilsson},
title = {A Minimum Residual Interpolation Method for Linear
Equations with Multiple Right Hand Sides},
institution = it,
department = tdb,
year = 2002,
number = {2002-041},
month = dec,
annote = {AMS subject classification (MSC2000): 65F10, 65R20,
78M05},
abstract = {An efficient method for solution of systems of linear
equations with many right hand sides is developed. The
right hand sides are assumed to depend smoothly on a
parameter. The equations are solved by an iterative method
and a linear least squares approximation is used as initial
guess. The work spent on the iterations is bounded
independently of the number of right hand sides. The method
is applied to the solution of Maxwell's equations of
electromagnetics in the frequency domain. The efficiency of
the method is illustrated by computing the monostatic radar
cross section around an aircraft model. }
}
@TechReport{ it:2002-040,
author = {Torsten S{\"o}derstr{\"o}m},
title = {Why are errors-in-variables problems often tricky?},
institution = it,
department = syscon,
year = 2002,
number = {2002-040},
month = nov,
abstract = {There are several identification methods designed for the
errors-in-variables problem. In this paper we focus on
discussing the underlying assumptions for several of these
methods. Some assumptions are shown to have far reaching
consequences. For example, if the noise-free input happens
to be periodic, simple estimators that give consistent
parameter estimates of the system parameters can easily be
designed. If the variances of the input and output noises
are unknown, some structural assumption must be added for
the system dynamics to be identifiable. On the other hand,
should the ratio between output noise variance and input
noise variance be known, it is possible not only to
estimate the system parameters consistently, but also to
combine this with a reasonable estimate of the unperturbed
input. }
}
@TechReport{ it:2002-039,
author = {R. Blaheta and S. Margenov and M. Neytcheva},
title = {Uniform estimate of the constant in the strengthened {CBS}
inequality for anisotropic non-conforming {FEM} systems},
institution = it,
department = tdb,
year = 2002,
number = {2002-039},
month = nov,
abstract = {Preconditioners based on various multilevel extensions of
two-level finite element methods (FEM) lead to iterative
methods which have an optimal order computational
complexity with respect to the size of the system. Such
methods were first presented in \cite{AV1,AV2}, and are
based on (recursive) two-level splittings of the finite
element space. The key role in the derivation of optimal
convergence rate estimates plays the constant $\gamma$ in
the so-called Cauchy-Bunyakowski-Schwarz (CBS) inequality,
associated with the angle between the two subspaces of the
splitting. It turns out that only existence of uniform
estimates for this constant is not enough and accurate
quantitative bounds for $\gamma$ have to be found as well.
More precisely, the value of the upper bound for $\gamma\in
(0,1)$ is a part of the construction of various multilevel
extensions of the related two-level methods.
In this paper an algebraic two-level preconditioning
algorithm for second order elliptic boundary value problems
is constructed, where the discretization is done using
Crouzeix-Raviart non-conforming linear finite elements on
triangles. An important point to make is that in this case
the finite element spaces corresponding to two successive
levels of mesh refinements are not nested. To handle this,
a proper two-level basis is considered, which enables us to
fit the general framework for the construction of two-level
preconditioners for conforming finite elements and to
generalize the method to the multilevel case.
The major contribution of this paper is the derived
estimates of the related constant $\gamma$ in the
strengthened CBS inequality. These estimates are uniform
with respect to both coefficient and mesh anisotropy. Up to
our knowledge, the results presented in the paper are the
first for non-conforming FEM systems. }
}
@TechReport{ it:2002-038,
author = {Parosh Aziz Abdulla and Alexander Rabinovich},
title = {Verification of Probabilistic Systems with Faulty
Communication},
institution = it,
department = docs,
year = 2002,
number = {2002-038},
month = nov,
abstract = {Many protocols are designed to operate correctly even in
the case where the underlying communication medium is
faulty. To capture the behaviour of such protocols,
\textit{lossy channel systems (LCS)} \cite{AbJo:lossy:IC}
have been proposed. In an LCS the communication channels
are modelled as FIFO buffers which are unbounded, but also
unreliable in the sense that they can nondeterministically
lose messages.
Recently, several attempts \cite{BaEn:plcs,ABIJ:problossy}
have been made to study \textit{probabilistic Lossy Channel
Systems (PLCS)} in which the probability of losing messages
is taken into account. In this paper, we consider a variant
of PLCS which is more realistic than those studied in
\cite{BaEn:plcs,ABIJ:problossy}. More precisely, we assume
that during each step in the execution of the system, each
message may be lost with a certain predefined probability.
We show that for such systems the following model checking
problem is decidable: to verify whether a given property
definable by finite state $\omega$-automata holds with
probability one. We also consider other types of faulty
behavior, such as corruption and duplication of messages,
and insertion of new messages, and show that the
decidability results extend to these models. }
}
@TechReport{ it:2002-037,
author = {Bob Melander and Mats Bj{\"o}rkman},
title = {Trace-Driven Network Path Emulation},
institution = it,
department = docs,
year = 2002,
number = {2002-037},
month = nov,
abstract = {This paper reports on on-going work where a trace-driven
approach to network path emulation is investigated. Time
stamped probe packets are sent along a network path whereby
a probe packet trace can be generated. It basically
contains the send times and the one-way delays/loss
indications of the probe packets. Inside the emulator, the
probe packet trace is used by a loss model and a delay
model. These determine if a packet should be dropped or
what the delay of the packet should be. Three loss models
and three delay models are evaluated. For non-responsive
UDP-based flows, the trace-driven loss and delay models
that determine loss and delay based on loss-rates and delay
distribution parameters calculated across the probe packet
trace using a small gliding window are found to perform
best. For adaptive TCP flows, none of the evaluated
trace-driven models performs well. Instead, the Bernoulli
loss model and an independent average delay model performs
best.}
}
@TechReport{ it:2002-036,
author = {Bernhard M{\"u}ller},
title = {Control Errors in {CFD!}},
institution = it,
department = tdb,
year = 2002,
number = {2002-036},
month = oct,
note = {Invited lecture to appear in the Proceedings of the 20th
Aerospace Numerical Simulation Symposium at the National
Aerospace Laboratory of Japan, held in Tokyo on July 3-5,
2002},
abstract = {Error control in computational fluid dynamics (CFD) has
been crucial for reliability and efficiency of numerical
flow simulations. The roles of truncation and rounding
errors in difference approximations are discussed.
Truncation error control is reviewed for ODEs. For
difference approximations of PDEs, discretization error
control by Richardson extrapolation is outlined.
Applications to anisotropic grid adaptation in CFD are
shown. Alternative approaches of error control in CFD are
mentioned.}
}
@TechReport{ it:2002-035,
author = {Ken Mattsson and Magnus Sv{\"a}rd and Mark Carpenter and
Jan Nordstr{\"o}m},
title = {Accuracy Requirements for Steady and Transient
Aerodynamics},
institution = it,
department = tdb,
year = 2002,
number = {2002-035},
month = oct,
abstract = {A numerical study on the benefit of high order methods is
performed. Numerical computations of solutions governed by
the Euler equations are performed. The propagation of a
vortex convected through an empty domain, computations of
steady state solutions around a NACA0012 airfoil and
vortex-airfoil interaction are considered. These
computations show that high order methods are often
required in order to capture the significant flow features,
especially for transient problems. }
}
@TechReport{ it:2002-034,
author = {Stefan Johansson},
title = {Numerical Solution of the Linearized Euler Equations Using
High Order Finite Difference Operators with the Summation
by Parts Property},
institution = it,
department = tdb,
year = 2002,
number = {2002-034},
month = oct,
note = {Updated version, March 2003, available at
\url{http://www.it.uu.se/research/publications/reports/2002-034/2002-034-updated}
(PDF and Postscript)},
abstract = {We have used high order finite difference methods with the
summation by parts property (SBP) on the 1D linearized
Euler equations. The boundary conditions are imposed with
both the projection method and the simultaneous
approximation term method (SAT) for comparison. The formal
fourth order of accuracy of the high order SBP operator was
verified with both the projection method and the SAT
method. Some relatively large errors were observed at the
artificial boundaries and further investigations are needed
to improve the non-reflecting boundary conditions. }
}
@TechReport{ it:2002-033,
author = {Henrik Bj{\"o}rklund and Sven Sandberg and Sergei
Vorobyov},
title = {Memoryless Determinacy of Parity and Mean Payoff Games: A
Simple Proof},
institution = it,
department = csd,
year = 2002,
number = {2002-033},
month = oct,
note = {Updated journal version, March 2003, available at
\url{http://www.it.uu.se/research/publications/reports/2002-033/2002-033-journal}}
,
abstract = {We give a simple, direct, and constructive proof of
memoryless determinacy for Parity and Mean Payoff Games.
First, we prove by induction that the finite-duration
versions of these games, played until some vertex is
repeated, are determined and both players have memoryless
winning strategies. In contrast to
[Ehrenfeucht-Mycielski79], our proof does not refer to the
infinite-duration versions. Second, we show that the
results straightforwardly generalize to infinite duration
games.}
}
@TechReport{ it:2002-032,
author = {Carl {\AA}borg and Anders Billing},
title = {Health Problems with Electronic Document Handling: a
longitudinal study},
institution = it,
department = hci,
year = 2002,
number = {2002-032},
month = oct,
abstract = {This study shows that electronic document handling (EDH)
systems can result in increased risks of work-related
musculoskeletal disorders, especially ``mouse-arm
syndrome'', and stress-related mental and somatic symptoms.
The effects of introducing an EDH system on the physical
and psychosocial work environment, as well as on
self-reported health and well being, were studied at four
Swedish work places where clerical duties are performed.
Data were collected on three separate occasions: before and
6 and 18 months after the introduction of the EDH system.
The methods used were interviews, observation interviews,
questionnaires, video recordings, technical measurements
and expert observation and examination. The results showed
an increase in time spent at visual display units (VDUs)
and longer periods without taking a break at the VDUs after
introduction of the EDH system. Moreover, after the
introduction of the EDH system, all of the data collection
methods indicated (a) an increase in workload, (b) a
greater number of repetitive and monotonous tasks, (c)
participants felt more constrained, (d) a higher frequency
in static work postures and (e) a diminution in task
variability. The questionnaires revealed an increase in
musculoskeletal symptoms and in psychological and
psychosomatic complaints. The introduction of EDH systems
can improve the effectiveness of work over the short run,
but in order not to risk the health of the users an
ergonomic strategy for the design of work organization,
work systems, computer systems, job tasks and workstations
is necessary.
Keywords: Information technology, electronic document
handling, physical and psychosocial work environment,
health and well being, musculoskeletal disorders. }
}
@TechReport{ it:2002-031,
author = {Carl {\AA}borg and Elisabeth Fernstr{\"o}m and Mats
Ericson},
title = {Telework Work Environment and Well Being: A Longitudinal
Study},
institution = it,
department = hci,
year = 2002,
number = {2002-031},
month = oct,
abstract = { The aim of this study is to analyse the effects that
part-time telecommuting from home will have on office
workers' physical and psychosocial work environment, at
home and at the ordinary workplace, as well as on their
general well being. Twenty-eight employees from two
organizations were followed for a 2-year period. Diaries,
interviews, and expert evaluation were used to collect
data. Participants experienced part-time (1-2 days per
week) telework from home as being helpful in obtaining a
balance between work and leisure time, and in being more
effective in their work. The participants worked more hours
at home, worked long hours without breaks, and worked late
at night and on the weekends at home. The workstation was
seldom as good ergonomically at home as at the office. All
the respondents experienced problems with the computer
equipment and computer system.
Conclusions: Introducing telework can enhance work
effectiveness; however, it can also result in both an
increase in workload and various work-related health risks.
}
}
@TechReport{ it:2002-030,
author = {Henrik Bj{\"o}rklund and Sven Sandberg and Sergei
Vorobyov},
title = {An Experimental Study of Algorithms for Completely
Unimodal Optimization},
institution = it,
department = csd,
year = 2002,
number = {2002-030},
month = oct,
abstract = {The paper presents an account of the experimental study of
five different algorithms for the Completely Unimodal
Pseudoboolean Function (CUPBF) Optimization. CUPBFs satisfy
the Hirsch's conjecture, but are not known (although
conjectured) to be polynomial. We summarize known and new
upper and lower bounds, describe methods of random CUPBFs
generation, and use them to compare the algorithms. }
}
@TechReport{ it:2002-029,
author = {Bengt Eliasson},
title = {Domain Decomposition of the {P}ad{\'e} Scheme and
Pseudo-Spectral Method, Used in {V}lasov Simulations},
institution = it,
department = tdb,
year = 2002,
number = {2002-029},
month = oct,
abstract = {In order to evaluate parallel algorithms for solving the
Vlasov equation numerically in multiple dimensions, the
algorithm for solving the one-dimensional Vlasov equation
numerically has been parallelised. The one-dimensional
Vlasov equation leads to a problem in the two-dimensional
phase space $(x,v)$, plus time. The parallelisation is
performed by domain decomposition to a rectangular
processor grid. Derivatives in $x$ space are calculated by
a pseudo-spectral method, where FFTs are used to perform
discrete Fourier transforms. In velocity $v$ space a
Fourier method is used, together with the compact Pad{\'e}
scheme for calculating derivatives, leading to a large
number of tri-diagonal linear systems to be solved. The
parallelisation of the tri-diagonal systems in the Fourier
transformed velocity space can be performed efficiently by
the method of domain decomposition. The domain
decomposition gives rise to Schur complement systems, which
are tri-diagonal, symmetric and strongly diagonally
dominant, making it possible to solve these systems with a
few Jacobi iterations. Therefore, the parallel efficiency
of the semi-implicit Pad{\'e} scheme is comparable to the
parallel efficiency of explicit difference schemes. The
parallelisation in $x$ space is less effective due to the
FFTs used. The code has been tested on shared memory
computers, on clusters of computers, and with the help of
the Globus toolkit for communication over the Internet. }
}
@TechReport{ it:2002-028,
author = {Bengt Eliasson},
title = {Numerical Modelling of the Two-Dimensional
{V}lasov-{M}axwell System},
institution = it,
department = tdb,
year = 2002,
number = {2002-028},
month = oct,
abstract = {The two-dimensional Vlasov-Maxwell system for a plasma
with mobile, magnetised electrons and ions, is investigated
numerically. Special attention is paid to the conservation
of the divergences of the electric and magnetic fields in
the Maxwell equations. The Maxwell equations are rewritten,
by means of the Lorentz potentials, in a form which
conserves these divergences. Linear phenomena are
investigated numerically and compared with theory and with
previous numerical results. }
}
@TechReport{ it:2002-027,
author = {Markus Nord{\'e}n and Sverker Holmgren and Michael
Thun{\'e}},
title = {{OpenMP} versus {MPI} for {PDE} Solvers Based on Regular
Sparse Numerical Operators},
institution = it,
department = tdb,
year = 2002,
number = {2002-027},
month = oct,
abstract = {Two parallel programming models represented by OpenMP and
MPI are compared for PDE solvers based on regular sparse
numerical operators. As a typical representative of such an
operator, a finite difference approximation of the Euler
equations for fluid flow is considered.
The comparison of programming models is made with regard to
uniform memory access (UMA), non-uniform memory access
(NUMA), and self optimizing NUMA (NUMA-opt) computer
architectures. By NUMA-opt, we mean NUMA systems extended
with self optimization algorithms, in order to reduce the
non-uniformity of the memory access time.
The main conclusions of the study are: (1) that OpenMP is a
viable alternative to MPI on UMA and NUMA-opt
architectures, (2) that OpenMP is not competitive on NUMA
platforms, unless special care is taken to get an initial
data placement that matches the algorithm, and (3) that for
OpenMP to be competitive in the NUMA-opt case, it is not
necessary to extend the OpenMP model with additional data
distribution directives, nor to include user-level access
to the page migration library. }
}
@TechReport{ it:2002-026,
author = {Henrik Bj{\"o}rklund and Sven Sandberg and Sergei
Vorobyov},
title = {A Discrete Subexponential Algorithm for Parity Games},
institution = it,
department = csd,
year = 2002,
number = {2002-026},
month = sep,
abstract = { We suggest a new randomized algorithm for solving Parity
Games with the worst case time complexity roughly
\[\min\left(O\left( n^3 \cdot \left( \frac{n}{k}+1
\right)^k \right), \;2^{O(\sqrt{n\log n})}\right),\] where
$n$ is the number of vertices and $k$ the number of colors
of the game. Comparable with the previously known
algorithms, which are efficient when the number of colors
is small, it is subexponential when the number of colors is
large, $k = \Omega(n^{1/2 + \varepsilon})$. }
}
@TechReport{ it:2002-025,
author = {Paul Petterson and Wang Yi (eds.)},
title = {Workshop on Real-Time Tools (Proceedings)},
institution = it,
department = docs,
year = 2002,
number = {2002-025},
month = jul,
abstract = {Proceedings of the 2nd workshop on Real-Time Tools
(RT-TOOLS), arranged in Copenhagen, Denmark, August 1 2002
in association with the 14th conference on Computer-Aided
Verification (CAV).}
}
@TechReport{ it:2002-024,
author = {Jakob Engblom and Magnus Nilsson},
title = {Time Accurate Simulation: Making a {PC} Behave Like a
8-Bit Embedded {CPU}},
institution = it,
department = docs,
year = 2002,
number = {2002-024},
month = jul,
abstract = {When developing embedded systems, developers often use
simulation techniques to allow development to proceed
without access to the target hardware. To make use of the
high quality development tools available on the PC
platform, one popular simulation method is to compile the
code intended for the target system to run on the PC,
allowing the development of the software to proceed on the
PC without use of the final target system. For a
distributed system, each target node is given its own
process on the host PC, with software on the PC simulating
the communications network.
We have extended one such simulation environment to include
the aspect of relative and absolute processing speed of the
target systems, allowing for a more accurate simulation
where not only functional but also timing-related bugs can
be found and diagnosed. The absolute time mode makes the
software on the PC run at the same speed as the real
target, thus allowing the mixing of simulated nodes with
real target hardware in the same system setup. The method
is applicable to any embedded processor, as long as it is
significantly slower than the PC. The system has been
implemented and tested on standard PCs running the Windows
NT operating system, and is currently being used in
industrial projects. }
}
@TechReport{ it:2002-023,
author = {Lars Ferm and Per L{\"o}tstedt},
title = {Anisotropic grid adaptation for Navier-Stokes' equations},
institution = it,
department = tdb,
year = 2002,
number = {2002-023},
month = jun,
abstract = {Navier-Stokes' equations are discretized in space by a
finite volume method. Error equations are derived which are
approximately satisfied by the errors in the solution. The
dependence of the solution errors on the discretization
errors is analyzed in certain flow cases. The grid is
adapted based on the estimated discretization errors. The
refinement and coarsening of the grid are anisotropic in
the sense that it is different in different directions in
the computational domain. The adaptation algorithm is
applied to laminar, viscous flow over a flat plate, in a
channel with a bump, and around a cylinder and an airfoil.
}
}
@TechReport{ it:2002-022,
author = {Henrik Lundgren and Erik Nordstr{\"o}m and Christian
Tschudin},
title = {Coping with Communication Gray Zones in {IEEE} 802.11b
based Ad hoc Networks},
institution = it,
department = docs,
year = 2002,
number = {2002-022},
month = jun,
abstract = {Our experiments with IEEE 802.11b based wireless ad hoc
networks show that neighbor sensing with broadcast messages
introduces ``communication gray zones'': in such zones data
messages cannot be exchanged although the HELLO messages
indicate neighbor reachability. This leads to a systematic
mismatch between the route state and the real world
connectivity, resulting in disruptive behavior for some ad
hoc routing protocols. Concentrating on AODV we explore
this issue and evaluate three different techniques to
overcome the gray zone problem. We present quantitative
measurements of these improvements and discuss the
consequences for ad hoc routing protocols and their
implementations. }
}
@TechReport{ it:2002-021,
author = {Johan Runeson and Sven-Olof Nystr{\"o}m},
title = {Generalizing Chaitin's Algorithm: Graph-Coloring Register
Allocation for Irregular Architectures},
institution = it,
department = csd,
year = 2002,
number = {2002-021},
month = may,
abstract = {We consider the problem of generalizing Chaitin-style
graph-coloring register allocation to the irregular
architectures used in embedded systems. A class of formal
machine descriptions is introduced, capable of describing a
wide range of irregular architectures. We extend Chaitin's
register allocation algorithm to handle any architectural
constraints that can be expressed using these machine
descriptions. The generalized algorithm is applicable to a
wider range of architectures and systems than any other
adaptation of Chaitin's algorithm found in the literature.
We argue that the modifications to the original algorithm
can be combined with most important extensions to Chaitin's
framework, for example coalescing and optimistic coloring.
}
}
@TechReport{ it:2002-020,
author = {Tobias Amnell and Elena Fersman and Paul Pettersson and
Hongyan Sun and Wang Yi},
title = {Code Synthesis for Timed Automata},
institution = it,
department = docs,
year = 2002,
number = {2002-020},
month = may,
abstract = {We present a framework for development of real-time
embedded systems based on the recently presented model of
timed automata extended with real-time tasks. It has been
shown previously that design problems such as reachability
and schedulability are decidable for the model of timed
automata with tasks. In this paper we describe how to
automatically synthesise executable code with predictable
timing behaviour, which is guaranteed to meet constraints
(timing and other) imposed on the design model. To
demonstrate the applicability of the framework, implemented
in the Times tool, we present a case-study of a well known
production cell, built in LEGO and controlled by a Hitachi
H8 based LEGO Mindstorm control brick. }
}
@TechReport{ it:2002-019,
author = {Erik B{\"a}ngtsson and Daniel Noreland and Martin
Berggren},
title = {Shape optimization of an acoustic horn},
institution = it,
department = tdb,
year = 2002,
number = {2002-019},
month = may,
abstract = {Shape optimization of an acoustic horn is performed with
the goal to minimize the portion of the wave that is
reflected. The analysis of the acoustical properties of the
horn is performed using a finite element method for the
Helmholtz equation.
The optimization is performed employing a BFGS Quasi-Newton
algorithm, where the gradients are provided by solving the
associated adjoint equations. To avoid local solutions to
the optimization problem corresponding to irregular shapes
of the horn, a filtering technique is used that applies
smoothing to the design updates and the gradient. This
smoothing technique can be combined with Tikhonov
regularization. However, experiments indicate that
regularization is redundant for the optimization problems
we consider here. However, the use of smoothing is crucial
to obtain sensible solutions. The smoothing technique we
use is equivalent to choosing a representation of the
gradient of the objective function in an inner product
involving second derivatives along the design boundary.
Optimization is performed for a number of single
frequencies as well as for a band of frequencies. For
single frequency optimization, the method shows
particularly fast convergence with indications of
super-linear convergence close to optimum. For optimization
on a range of frequencies, a design was achieved providing
a low and even reflection throughout the entire frequency
band of interest.}
}
@TechReport{ it:2002-018,
author = {Henrik Bj{\"o}rklund and Sven Sandberg and Sergei
Vorobyov},
title = {Optimization on Completely Unimodal Hypercubes},
institution = it,
department = csd,
year = 2002,
number = {2002-018},
month = may,
abstract = {We investigate and compare, both theoretically and
practically, several old and new algorithms for the
completely unimodal pseudo-boolean function optimization
problem. We settle the first nontrivial upper bounds for
two well-known local search algorithms, the Random and the
Greedy Single Switch algorithms. We also present the new
Random Multiple and All Profitable Switches algorithms.
These are not local search-type algorithms, and have not
been previously considered for this problem. We justify the
algorithms and show nontrivial upper bounds. In particular
we prove a $O(2^{0.775n})$ bound for the Random Multiple
Switches Algorithm, and also use random sampling to improve
the bounds for all above algorithms. In particular we give
a $O(2^{0.46n}) = O(1.376^n)$ upper bound for the Random
Multiple Switches Algorithm with Random Sampling.
We also show how Kalai-Ludwig's algorithm for Simple
Stochastic Games \cite{Ludwig95} can be modified to solve
the problem at hand, and that the modified algorithm
preserves the subexponential, $2^{O(\sqrt{n})}$, running
time.
We introduce and justify a new method for random generation
of `presumably hard' completely unimodal pseudo-boolean
functions. We also present experimental results indicating
that all the above algorithms perform well in practice. The
experiments, surprisingly, show that in all generated
example cases, the subexponential Kalai-Ludwig's algorithm
is outperformed by all the other algorithms. }
}
@TechReport{ it:2002-017,
author = {Eva Olsson and Stefan Seipel and Anders Jansson and Bengt
Sandblad},
title = {The Windscreen Used as a Display for Navigation
Information. An introductory study},
institution = it,
department = hci,
year = 2002,
number = {2002-017},
month = may,
abstract = {Grounding and collision are, next to fire, threats to a
safe journey. The navigator needs to know exactly where the
ship is and that the ship is on the expected route, which
means that there is no risk for grounding, and finally that
interference with surrounding traffic is avoided.
Navigators may suffer from loss of important information,
for instance in situations where visibility is reduced and
in darkness. In addition to watching the surroundings, the
navigator needs to monitor the radar screen and, more
frequently, an electronic chart display (ECDIS). These
displays provide information but the monitoring and
managing of the displays may reduce the navigator's
attention on the surrounding world. A recent accident
report (Investigation report C4/1998) pointed out that
adjustment of sea clutter required the navigator to go
through five separate steps on the radar equipment.
Accidents have also happened where the navigator in the
course of events have been preoccupied with e.g. adjustment
of radar screen clutter (MS Sleipner, 2000).
The solution suggested here integrates information from a
number of sources and presents safety-critical navigational
information on the windscreen in front of the navigator.
Such information can consist of markings for navigable
channel, contours and waypoints of a pre-defined route,
contours of shorelines and rocks, wrecks etc., and possibly
heading and speed of surrounding vessels as well as
information regarding the potential threat from an oncoming
vessel. It is important that the projected objects are
subtle and do not interfere with the navigator's focus on
the real world.
The different pieces of information presented in the
navigator's visual field will be picked up from DGPS/GPS,
transponders, radar, ARPA and electronic chart systems
(ECDIS). In the experiment reported here a Plexiglas
display covered with holographic film was used as the
windscreen that safety critical information was projected
on. Tracking equipment was used to let the navigator move
freely and continuously have the enhanced information in
the correct position, as an overlay on the real world. }
}
@TechReport{ it:2002-016,
author = {Fredrik Edelvik},
title = {A New Technique for Accurate and Stable Modeling of
Arbitrarily Oriented Thin Wires in the FDTD Method},
institution = it,
department = tdb,
year = 2002,
number = {2002-016},
month = apr,
abstract = {A subcell model for thin wires in the finite-difference
time-domain (FDTD) method using modified telegraphers
equations has been developed by Holland et al. In this
paper we present an extension of their algorithm, which
allows arbitrarily located and oriented wires with respect
to the Cartesian grid. This is important to be able to
accurately model wires that cannot be aligned to the
Cartesian grid, e.g.\ tilted wires and circular loop wires.
A symmetric coupling between field and wires yields a
stable time-continuous field-wire system and the fully
discrete field-wire system is stable under a CFL condition.
The accuracy and excellent consistency of the proposed
method are demonstrated for dipole and loop antennas with
comparisons with the Method of Moments and experimental
data. }
}
@TechReport{ it:2002-015,
author = {Andreas Johnsson},
title = {Differentiated Security in Wireless Networks},
institution = it,
department = docs,
year = 2002,
number = {2002-015},
month = apr,
note = {M.Sc. thesis},
abstract = {This report presents a three step solution to the
differentiated security and self-configuration problem in
wireless network where users are able to come and go as
they wish. Differentiated security is about giving
different user's different access rights towards a
surrounding infrastructure. Access rights can in some
systems be bought and in others they may be related to a
users location or real life status. Self-configuration is
about minimizing the configuration effort needed by network
users.
First a generic architecture is presented, which provides
an abstract solution without any requirements on specific
techniques or tools. Thereafter a prototype specification
and a prototype implementation are derived from the
architecture. They show that the desired system is feasible
and relatively easy to construct, using well known tools
for resource discovery, security and address handling. }
}
@TechReport{ it:2002-014,
author = {Samuel Sundberg and Lina von Sydow},
title = {Analysis of a semi-Toeplitz preconditioner for a
convection-diffusion problem},
institution = it,
department = tdb,
year = 2002,
number = {2002-014},
month = apr,
abstract = {We have defined and analyzed a semi-Toeplitz
preconditioner for time-dependent and steady-state
convection-diffusion problems. The preconditioner exhibits
very good theoretical convergence properties. The analysis
is corroborated by numerical experiments. }
}
@TechReport{ it:2002-013,
author = {Jakob Engblom},
title = {Effects of Branch Predictors on Execution Time},
institution = it,
department = docs,
year = 2002,
number = {2002-013},
month = apr,
abstract = {This technical report describes the result of a short
experimental investigation into the effect of branch
predictors on the execution times of tight loops on modern
aggressive microprocessors. The same code was tried on
Pentium III, Athlon, UltraSparc II, and UltraSparc III
processors. For reference, the same experiment was carried
out on a simple V850E processor to determine the behaviour
without branch prediction.
The results indicate that advanced branch predictors give a
very high and hard-to-understand variation in the execution
time of loops, and that this effect can be very big
relative to the execution time of other instructions. }
}
@TechReport{ it:2002-012,
author = {Lars Ferm and Per L{\"o}tstedt},
title = {Accurate and Stable Grid Interfaces for Finite Volume
Methods},
institution = it,
department = tdb,
year = 2002,
number = {2002-012},
month = mar,
abstract = {A convection-diffusion equation is discretized by a finite
volume method in two space dimensions. The grid is
partitioned into blocks with jumps in the grid size at the
block interfaces. Interpolation in the cells adjacent to
the interfaces is necessary to be able to apply the
difference stencils. Second order accuracy is achieved and
the stability of the discretizations is investigated. The
interface treatment is tested in the solution of the
compressible Navier-Stokes equations. The conclusions from
the scalar equation are valid also for these equations. }
}
@TechReport{ it:2002-011,
author = {Sheayun Lee and Andreas Ermedahl and Sang Lyul Min and
Naehyuck Chang},
title = {Statistical Derivation of an Accurate Energy Consumption
Model for Embedded Processors},
institution = it,
department = docs,
year = 2002,
number = {2002-011},
month = mar,
abstract = {The energy consumption of software is becoming an
increasingly important issue in designing mobile embedded
systems where batteries are used as the main power source.
As a consequence, recently, a number of promising
techniques have been proposed to optimize software for
reduced energy consumption. Such low-power software
techniques require an energy consumption model that can be
used to identify the factors contributing to the overall
energy consumption. We propose a technique to derive an
accurate energy consumption model by abstracting the energy
behavior of the target processor. The proposed approach
combines empirical measurement with a statistical analysis
technique to approximate the actual energy consumption,
whose result is a model equation that can be used to
estimate software energy consumption. The model equation
also provides insightful information that can be used in
program optimization for low energy, by identifying the
factors affecting the energy consumption of software.
Experimental results show that the model equation can
accurately estimate the energy consumption of a random
instruction sequence, with an average error of 2.5\%. }
}
@TechReport{ it:2002-010,
author = {Jonas Boustedt},
title = {Automated Analysis of Dynamic Web Services},
institution = it,
year = 2002,
number = {2002-010},
month = mar,
note = {M.Sc. thesis},
abstract = {For a web application test-engineer, it would be
convenient to have a map, in form of a graph, describing
the functional topology of the application. In that way, it
would be possible to analyse the possible paths which can
be navigated to discover redundancies and circularities for
example. A web spider tool can automate the construction of
such a graph. The spider can request a document from the
application, find all references to other documents in it,
and explore them recursively until all the references have
been analysed. However, web services often produce dynamic
responses which means that the content cannot be distinctly
represented by its reference, i.e., the responses must be
classified in a way that matches the users perception. The
main problem is to find suitable criteria for this
classification. This study describes how to make such a
tool and it surveys ideas for how to create a classifying
identifier for dynamic responses. The implemented spider
was used to make experiments on selected web services,
using different models for web node identification. The
result is a proposal of suitable criteria for
classification of dynamic responses, coming from web
applications. These criteria are implemented in algorithms
which use the parse structure and the set of internal
references as the dominant terms of identification. }
}
@TechReport{ it:2002-009,
author = {Andy Bavier and Thiemo Voigt and Mike Wawrzoniak and Larry
Peterson and Per Gunningberg},
title = {{SILK}: Scout Paths in the Linux Kernel},
institution = it,
department = docs,
year = 2002,
number = {2002-009},
month = feb,
abstract = {SILK stands for Scout In the Linux Kernel, and is a port
of the Scout operating system to run as a Linux kernel
module. SILK forms a replacement networking subsystem for
standard Linux 2.4 kernels. Linux applications create and
use Scout paths via the Linux socket interface with
virtually no modifications to the applications themselves.
SILK provides Linux applications with the benefits of Scout
paths, including early packet demultiplexing, per-flow
accounting of resources, and explicit scheduling of network
processing. SILK also introduces the concept of an
\emph{extended path} to provide a framework for application
QoS. We demonstrate the utility of SILK by showing how it
can provide QoS for the Apache Web server. }
}
@TechReport{ it:2002-008,
author = {Henrik Bj{\"o}rklund and Sergei Vorobyov},
title = {Two Adversary Lower Bounds for Parity Games},
institution = it,
department = csd,
year = 2002,
number = {2002-008},
month = feb,
abstract = {By using the adversary arguments we settle the first
exponential lower bounds for restricted classes of
algorithms solving Parity Games The first result applies to
any algorithms that rely only on estimating values of
vertices from the viewpoint of one player and ignore the
game graph structure (a rough abstraction of different
fix-point algorithms), the second settles the lower bound
for a randomized algorithm that samples from the set of
optimal counterstrategies (a popular idea used in many
approaches). }
}
@TechReport{ it:2002-007,
author = {F. Edelvik and G. Ledfelt and P. L{\"o}tstedt and D. J.
Riley},
title = {An Unconditionally Stable Subcell Model for Arbitrarily
Oriented Thin Wires in the FETD Method},
institution = it,
department = tdb,
year = 2002,
number = {2002-007},
month = feb,
abstract = {A computational subcell model for thin wires is developed
for electromagnetic simulations. The Maxwell equations are
discretized by a finite element approximation on a
tetrahedral grid. The wires are described by a second-order
equation for the current. The geometry of the wires can be
chosen independent of the volume grid. A symmetric coupling
between field and wires yields a stable semi-discrete
field-wire system and an unconditionally stable fully
discrete field-wire system. The system of equations is in
each time step solved by a preconditioned conjugate
gradient method. The accuracy of the subcell model is
demonstrated for dipole and loop antenna with comparisons
with the Method of Moments and experimental data. }
}
@TechReport{ it:2002-006,
author = {Anders Berglund},
title = {How do students understand network protocols? A
phenomenographic study},
institution = it,
department = docs,
year = 2002,
number = {2002-006},
month = feb,
abstract = {University students' understanding of network protocols is
in focus in this report. With an overall aim to improve
learning and teaching in computer systems at a university
level, an empirically based study has been performed. In
the study, the different ways in which students understand
three specific network protocols -- TCP, UDP and RMI -- as
well as the general concept of a network protocol have been
investigated with a phenomenographic research approach.
Qualitatively different ways of understanding or
experiencing network protocols are discerned. The
identified critical differences between the understandings
are ``how'' or ``as what'' the protocols are understood,
``as a part of which framework'' the protocols exist, and
``in what way'' the protocols are described. Although
experienced as different, the three protocols are
understood as being parts of similarly frameworks.
Recommendations for teaching of computer systems in
distributed projects are made, based on the results.
Universities should teach computer networks in a way that
encourages students to understand network protocols in
these critically different ways, and that stimulates them
to shift between these ways depending on the task at
hand.}
}
@TechReport{ it:2002-005,
author = {Kajsa Ljungberg and Sverker Holmgren and {\"O}rjan
Carlborg},
title = {Efficient Kernel Algorithms for QTL Mapping Problems},
institution = it,
department = tdb,
year = 2002,
number = {2002-005},
month = feb,
abstract = {The advent of sophisticated and powerful methods for
molecular genetics pushes the need for efficient methods
for data analysis. Advanced algorithms are necessary for
extracting all possible information from laboriously
obtained data sets. We present a general linear algebra
framework for QTL mapping, applicable to many commonly used
methods, using both linear regression and maximum
likelihood estimation. The formulation simplifies future
comparisons between and analyses of the methods. We show
how the common structure of QTL analysis models can be used
to improve the kernel algorithms, drastically reducing the
computational effort while retaining the original analysis
results. We have evaluated our new algorithms on data sets
originating from two large F$_2$ populations of domestic
animals. Using an updating approach, we show that 1-3
orders of magnitude reduction in computational demand can
be achieved for matrix factorizations. For interval
mapping/composite interval mapping settings using a maximum
likelihood model, we also show how to use the original EM
algorithm instead of the ECM approximation, significantly
improving the convergence and introducing an additional
reduction in the computational time. The algorithmic
improvements makes it feasible to perform analyses
previously deemed impractical or even impossible. For
example, using the new algorithms it is reasonable to
perform permutation testing using exhaustive search on
populations of 200 individuals for fully epistatic two-QTL
models with a large number of parameters. }
}
@TechReport{ it:2002-004,
author = {Mats L{\"o}fberg and Jan Gulliksen and Torsten Norlander},
title = {Anv{\"a}ndare i systemutvecklingsprocessen - ett
fenomenologiskt perspektiv},
institution = it,
department = hci,
year = 2002,
number = {2002-004},
month = feb,
note = {In Swedish},
abstract = {This study has been accomplished through the Department of
Psychology, Institution of Social Science, University of
Karlstad. The study is further presented as a part of the
VERKA-project, Department of Human-Computer Interaction
(HCI), Institution of Information Technology, Uppsala
University.
The aim of the study is to examine how user participation
in systems development can successfully be accomplished.
Another purpose is the development of guidelines in user
centred systems design. The result is analysed and
described from a psychological perspective.
A qualitative method was deemed to be the appropriate way
to obtain data in the study. The empirical information was
collected through interviews. To analyse the material
Karlsson's Empirical Phenomenological Psychological Method
(the EPP-method) was used.
The respondents were participants in RSV's and RFV's
systems development projects under the VERKA-project at
Uppsala University. A total of 11 respondents participated
in the study.
Generally the respondents had a positive attitude towards
participating in systems development projects - even if the
work from time to time was considered burdensome. The
participants felt like equal members in the systems design
process, and they felt that their opinions were as
important as anyone else's. Another discovery was a role
division with the members of the systems development
project on one side and their former colleagues on the
other. An important part in future development processes
can be to inform user representatives about experiences
from earlier participants. The development of cooperation
between projects and former colleagues can have a positive
impact on acceptance, learning and attitudes. }
}
@TechReport{ it:2002-003,
author = {Ken Mattsson and Magnus Sv{\"a}rd and Jan Nordstr{\"o}m},
title = {Stable and accurate artificial dissipation},
institution = it,
department = tdb,
year = 2002,
number = {2002-003},
month = jan,
abstract = {Stability for nonlinear convection problems using centered
difference schemes require the addition of artificial
dissipation. In this paper we present dissipation operators
that preserve both stability and accuracy for high order
finite difference approximations of initial boundary value
problems. }
}
@TechReport{ it:2002-002,
author = {S. Seipel and M. Lindkvist},
title = {Methods and application of interactive 3D computer
graphics in anthropology},
institution = it,
department = hci,
year = 2002,
number = {2002-002},
month = jan,
abstract = {This report presents 3D computer graphics techniques for
interactive visual exploration of virtual mummies. It is
part of an exposition on the Cultural Heritage of the
Egyptian Mummies in the Museum Gustavianum, in Uppsala. We
describe a general-purpose projection metaphor for
correctly presenting virtual 3D images on the dissection
table of a historical anatomic theatre. This method allows
for dynamic off-axis perspective viewing situations as well
as it provides keystone correction for excessive projection
angles as necessitated by the specific installation
environment. For the application to reach out beyond the
scope of the exhibition, we developed an adaptive
image-based rendering approach that scales with the
performance of the rendering host. Based on dynamic mesh
simplification of the 3D mummy model, it automatically
performs re-projections of texture images in order to
maintain correct visual results. For interaction purposes
with a digitiser tablet we present a means of stroke-based
input that provides ease of use to non-expert visitors of
the exhibition.
The problems we address with this paper are not only of
interest for this particular application domain but
generally for all interactive graphical installations,
which must be adapted to the existing architectural
situation.}
}
@TechReport{ it:2002-001,
author = {S{\^o}nia M. Gomes and Bertil Gustafsson},
title = {Combining Wavelets with Finite Differences: Consistency
Analysis},
institution = it,
department = tdb,
year = 2002,
number = {2002-001},
month = jan,
abstract = {The method is an adaptive finite difference strategy for
numerical solution of evolution partial differential
equations. The principle is to represent the solution only
through those point values indicated by the significant
wavelet coefficients. Typically, few points are found in
each time step, the grid being coarse in smooth regions,
and refined close to irregularities. At each point, the
spatial derivatives are discretized by uniform finite
differences, using step size proportional to the point
local scale. Eventually, required neighboring stencils are
not present in the grid. In such case, the correspondig
point values are approximated from coarser scales by using
reconstruction operators defined by means of interpolating
subdivision scheme. Our purpose in this paper is to analyse
a generalization of the concept of truncation error, which
is the familiar basis of the analysis of difference
schemes. For this consistency analysis, we show that the
adaptive finite difference scheme can also be formulated in
terms of a collocation scheme for an adapted wavelet
expansion of the solution. For this purpose, we first prove
some results concerning the local behavior of the
reconstruction operators, which stand for appropiate
cone-like grids. }
}
@TechReport{ it:2001-030,
author = {Jakob Engblom and Andreas Ermedahl and Friedhelm
Stappert},
title = {Validating a Worst-Case Execution Time Analysis Method for
an Embedded Processor},
institution = it,
department = docs,
year = 2001,
number = {2001-030},
month = dec,
abstract = {Knowing the Worst-Case Execution Time (WCET) of a program
is necessary when designing and verifying real-time
systems. When evaluating WCET analysis methods, the common
methodology is to compare a WCET estimate with an execution
of the same program with known worst-case data on the
target hardware. This evaluation method is inadequate,
since errors in one part of the analysis might mask errors
occuring in other parts of the analysis.
In this paper we present a methodology for systematically
testing WCET analysis tools for modern pipelined
processors. The methodology is based on a decomposition of
WCET analysis into a set of components that should be
tested and validated in isolation. Our testing methodology
does not require that we have a perfect model of the
hardware, thus the validation of the hardware model is
considered as a separate problem.
We apply the methodology to our previously published WCET
analysis method, and show that the pipeline analysis and
the calculation method we use are safe and produce tight
results.
We also show that our WCET analysis method can handle
programs containing nested loops, functions whose execution
times depend on parameters, multiway branches (switch
statements) and unstructured code. }
}
@TechReport{ it:2001-029,
author = {Henrik Lundgren and David Lundberg and Johan Nielsen and
Erik Nordström and Christian Tschudin},
title = {A Large-scale Testbed for Reproducible Ad hoc Protocol
Evaluations},
institution = it,
department = docs,
year = 2001,
number = {2001-029},
month = nov,
note = {A shorter version of this paper is accepted for
publication in the proceedings of IEEE WCNC'02},
abstract = {We have built an Ad hoc Protocol Evaluation testbed (APE)
in order to perform large-scale, reproducible experiments.
APE aims at assessing several different routing protocols
in a \emph{real world} environment instead of by
simulation. We present the APE testbed architecture and
report on initial experiments with up to 37 physical nodes
that show the reproducibility and scalability of our
approach. Several scenario scripts have been written that
include strict choreographic instructions to the testers
who walk around with ORiNOCO equipped laptops. We introduce
a metric called \emph{Virtual Mobility} that we use to
compare different testruns. This metric is based on the
\emph{measured} signal quality instead of the geometric
distance between nodes, hence it reflects how a routing
protocol actually \emph{perceives} the network's dynamics.}
}
@TechReport{ it:2001-028,
author = {Magnus Berggren},
title = {Wireless communication in telemedicine using Bluetooth and
{IEEE} 802.11b},
institution = it,
department = docs,
year = 2001,
number = {2001-028},
month = nov,
note = {M.Sc. thesis},
abstract = {This thesis explores the issues surrounding the
simultaneous deployment of Bluetooth \& Wireless LAN for
networked devices in a telemedicine environment. A key
aspect in telemedicine is the ability of the two standards
to co-exist in close proximity. This work defines
telemedicine, gives examples of applications, and describes
the two wireless techniques and the issues that arise when
considering the introduction of wireless communication.
The thesis tries to answer the question whether the two
wireless techniques Bluetooth and Wireless LAN (IEEE
802.11b) can co-exist in a telemedicine environment. In
order to do this, quantified measurements where performed
were the two wireless techniques where exposed to radio
interference from the other technique. These results are
printed as graphs and explained. }
}
@TechReport{ it:2001-027,
author = {K. Mahata and T. S{\"o}derstr{\"o}m and M. Mossberg and L.
Hillstr{\"o}m and S. Mousavi},
title = {On the use of flexural wave propagation experiments for
identification of complex modulus},
institution = it,
department = syscon,
year = 2001,
number = {2001-027},
month = nov,
note = {Also in the proceedings of 3rd International Conference on
Identification of Engineering System, Swansea 2002},
abstract = {In this paper, we investigate the estimation of the
complex modulus of a viscoelastic material from flexural
wave experiments. A bar specimen of uniform cross-section
is subjected to lateral impact by a steel ball giving rise
to flexural waves traveling along the bar. The strains due
to wave propagation are registered as functions of time
using strain gauges at different sections. The measured
strains are transformed in to the frequency domain. A
non-parametric estimation of the complex modulus is carried
out for each frequency. An analysis of the quality of the
non-parametric estimate is carried out. The validity of the
theoretical results are confirmed by numerical studies and
experimental tests. }
}
@TechReport{ it:2001-026,
author = {Jan Gulliksen and Inger Boivie},
title = {Usability Throughout the Entire Software Development
Lifecycle - A Summary of the {INTERACT} 2001 Workshop},
institution = it,
department = hci,
year = 2001,
number = {2001-026},
month = nov
}
@TechReport{ it:2001-025,
author = {Emmanuel Beffara and Sergei Vorobyov},
title = {Is Randomized Gurvich-Karzanov-Khachiyan's Algorithm for
Parity Games Polynomial?},
institution = it,
department = csd,
year = 2001,
number = {2001-025},
month = nov,
abstract = {We report on the experimental study of the
Gurvich-Karzanov-Khachiyan (\GKK) algorithm for cyclic
games adapted for \emph{parity games} (equivalent to the
$\mu$-calculus model checking), one of the major open
problems in complexity and automata theories,
computer-aided verification. The algorithms demonstrates
excellent polynomial (actually, a sublinear number of
iterations) behavior in a substantial (millions) number of
experiments with games of sizes up to 20.000 and 6 -- 7
colors. It also allows for a natural randomization. We
conducted extensive experiments of the randomized \GKK{}
algorithm on the `hard' Lebedev-Gurvich's game instances,
which force the deterministic version of the algorithm to
make \emph{exponentially} many iterations. With high
probability the algorithm converges after just a few
hundred iterations (compared with $2^{50}$ -- $2^{60}$ for
deterministic version). This allows for giving up
computations that converge slowly and restart with a fresh
initial potential transformation. While it remains to be
theoretically justified and proved, we present convincing
experimental data on dependency of the average and maximal
number of iterations on game sizes, outdegrees, colors,
initial randomizations. }
}
@TechReport{ it:2001-024,
author = {Larisa Beilina and Klas Samuelsson and Krister
{\AA}hlander},
title = {A hybrid method for the wave equation},
institution = it,
department = tdb,
year = 2001,
number = {2001-024},
month = oct,
note = {Also available as Preprint 2001-14 in Chalmers Finite
Element Center Preprint series},
abstract = {Hybrid finite element/finite difference simulation of the
wave equation is studied. The simulation method is hybrid
in the sense that different numerical methods, finite
elements and finite differences, are used in different
subdomains. The purpose is to combine the flexibility of
finite elements with the efficiency of finite differences.
The construction of proper geometry discretisations is
important for the hybrid approach. A decomposition of the
computational domain is described, which yields simple
communication between structured and unstructured
subdomains.
An explicit hybrid method for the wave equation is
constructed where the explicit finite difference schemes
and finite element schemes coincide for structured
subdomains. These schemes are used in the hybrid approach,
keeping finite differences on the structured subdomains and
applying finite elements on the unstructured domains. As a
consequence of the discretisation strategy, the resulting
hybrid scheme can be regarded as a pure finite element
scheme. Any numerical difficulties such as instabilities at
the interfaces are thus avoided.
The feasibility of the hybrid approach is illustrated by
numerous wave equation simulations in two and three space
dimensions. In particular, the approach can easily be used
for implementing absorbing boundary conditions.
The efficiency of different approaches is a key issue of
the current study. For our test cases, the hybrid approach
is about 5 times faster than a corresponding highly
optimised finite element method. It is concluded that the
hybrid approach may be an important tool to reduce the
execution time and memory requirement for this kind of
large scale computations. }
}
@TechReport{ it:2001-023,
author = {Pierre Flener and Alan Frisch and Brahim Hnich and Zeynep
Kiziltan and Ian Miguel and Toby Walsh},
title = {Matrix Modelling},
institution = it,
department = csd,
year = 2001,
number = {2001-023},
month = sep,
abstract = {We argue that constraint programs with one or more
matrices of decision variables provide numerous benefits,
as they share many patterns for which general methods can
be devised, such as for symmetry breaking. On a wide range
of real-life application domains, we demonstrate the
generality and utility of such matrix modelling. },
note = {Also released as Technical Report APES-36-2001 of the APES
group, 2001, available at
\url{http://www.dcs.st-and.ac.uk/~apes/reports/apes-36-2001.ps.gz}.
Appears in the Proceedings of the CP-01 Workshop on
Modelling and Problem Formulation. 7th International
Conference on the Principles and Practice of Constraint
Programming, 2001}
}
@TechReport{ it:2001-022,
author = {Pierre Flener and Alan Frisch and Brahim Hnich and Zeynep
Kiziltan and Ian Miguel and Justin Pearson and Toby Walsh},
title = {Symmetry in Matrix Models},
institution = it,
year = 2001,
number = {2001-022},
month = sep,
abstract = {Many constraint satisfaction problems (such as scheduling,
assignment, and configuration) can be modelled as
constraint programs based on matrices of decision
variables. In such matrix models, symmetry is an important
feature. We study and generalise symmetry-breaking
techniques, such as lexicographic ordering, and propose a
labelling technique achieving the same effect.},
note = {Also released as Technical Report APES-30-2001 of the APES
group, 2001, available at
\url{http://www.dcs.st-and.ac.uk/~apes/reports/apes-30-2001.ps.gz}.
Appears in the Proceedings of the CP-01 Workshop on
Symmetry in Constraints. 7th International Conference on
the Principles and Practice of Constraint Programming, 2001
}
}
@TechReport{ it:2001-021,
author = {Inger Boivie},
title = {Usability and Design Decisions in Software Development},
institution = it,
department = hci,
year = 2001,
number = {2001-021},
month = sep,
abstract = {Despite the attention that has been paid to usability in
the last few years, the world is still full of inadequate
software and frustrated users. The aim of this study was to
deepen the understanding of how usability matters are
handled in software development projects, particularly at
the Swedish National Tax Board (Riksskatteverket - RSV) and
the Swedish National Board for Social Securities
(Riksf{\"o}rs{\"a}kringsverket - RFV).
The main focus of the study was usability and interaction
design decisions in software development projects, that is,
considerations in the software development process that
have implications on the usability of the resulting system.
Who makes the decisions about the interaction design? When
are they made? What are the sources of input and the main
constraints? What support regarding usability matters does
the decision maker have access to?
The study was conducted by means of a series of
semi-structured interviews with eight developers and
usability people in the two organisations.
The study shows that there is no simple answer to who makes
the interaction design decisions and when they are made.
Rather, it is a case of everybody (developers and user
representatives) making this kind of decisions, all the
time. Many decisions are never made, they just happen as a
result of somebody coding a bit, or modelling a bit. The
matter of responsibility for the interaction design was
unclear, causing frustration. Use cases are the basis of
all design, and thus crucial to the usability of the
resulting system. But, use cases were reported to be
difficult write. They easily turn into ``system
operations'' providing little or no support for interaction
design.
One conclusion is that usability requires hands-on
activities throughout the project, or it ``gets lost'',
this is particularly important during construction. One way
of achieving continuous attention could be to incorporate a
usability role in the system development process and give
it sufficient status. }
}
@TechReport{ it:2001-020,
author = {Emmanuel Beffara and Sergei Vorobyov},
title = {Adapting {G}urvich-{K}arzanov-{K}hachiyan's Algorithm for
Parity Games: Implementation and Experimentation},
institution = it,
department = csd,
year = 2001,
number = {2001-020},
month = sep,
abstract = { We suggest and experimentally test a new approach to
solving the \textsc{Parity Games} problem, equivalent to
the \emph{propositional modal $\mu$-calculus}, a
fundamental problem in automata, games, complexity
theories, as well as in practical computer-aided
verification, whose precise computational complexity is a
long-standing open question.
Based on the algorithm due to Gurvich, Karzanov, and
Khachiyan for solving the more general \textsc{Mean Payoff
Games}, we make an adaptation and optimization for parity
games, implement it in Knuth's system CWEB of ``literate
programming'' using C++.
The algorithm is less known in the model-checking community
and is based on different ideas, as compared to the
well-investigated ideas including fixpoint iteration,
strategy improvement, dynamic programming.
Run on a considerable number (several millions) of randomly
generated test game instances with up to 20.000 vertices
and 6 -- 7 colors, the algorithm demonstrates a rapid
convergence with sublinear number of iterations. Moreover,
unlike other known algorithms, for which examples of
exponential behaviors are known, our algorithm admits
internal randomization, which gives improvements in our
tests and may help the algorithm to avoid bad cases.
Our experiments strongly suggest that the algorithm is
polynomial on the average under reasonable distributions,
which remains to be explained in further studies.
This report contains results of the summer project done by
the first author under the supervision and with
participation of the second author. It represents an
ongoing project, the new updates will be available from
\url{http://www.csd.uu.se/~vorobyov/eb-gkk} }
}
@TechReport{ it:2001-019,
author = {Wendy Kress and Jonas Nilsson},
title = {Boundary conditions and estimates for the linearized
{N}avier-{S}tokes equations on staggered grids},
institution = it,
department = tdb,
year = 2001,
number = {2001-019},
month = sep,
abstract = {In this paper we consider the linearized Navier-Stokes
equations in two dimensions under specified boundary
conditions. We study both the continuous case and a
discretization using a second order finite difference
method on a staggered grid and derive estimates for both
the analytic solution and the approximation on staggered
grids. We present numerical experiments to verify our
results. }
}
@TechReport{ it:2001-018,
author = {Emad Abd-Elrady},
title = {An adaptive grid point {RPEM} algorithm for harmonic
signal modeling},
institution = it,
department = syscon,
year = 2001,
number = {2001-018},
month = aug,
abstract = {Periodic signals can be modeled as a real wave with
unknown period in cascade with a piecewise linear function.
In this report, a recursive Gauss-Newton prediction error
identification algorithm for joint estimation of the
driving frequency and the parameters of the nonlinear
output function parameterized in a number of adaptively
estimated grid points is introduced. The Cramer-Rao bound
(CRB) is derived for the suggested algorithm. Numerical
examples indicate that the suggested algorithm gives better
performance than using fixed grid point algorithms and
easily can be modified to track both the fundamental
frequency variations and the time varying amplitude.}
}
@TechReport{ it:2001-017,
author = {Henrik Bj{\"o}rklund and Viktor Petersson and Sergei
Vorobyov},
title = {Experiments with Iterative Improvement Algorithms on
Completely Unimodal Hypercubes},
institution = it,
department = csd,
year = 2001,
number = {2001-017},
month = aug,
abstract = {Completely unimodal (i.e., having a unique local minimum
on every face) numberings of many-dimensional hypercubes
are abstract versions of different optimization problems,
like linear programming, decision problems for games, and
abstract optimization problems. In this paper we
investigate and compare the behaviors of seven iterative
improvement algorithms:
1) the Greedy Single Switch Algorithm (GSSA),
2) the Random Single Switch Algorithm (RSSA),
3) the All Profitable Switches Algorithm (APSA),
4) the Random Multiple Switches Algorithm (RMSA),
5) Kalai-Ludwig's Randomized Algorithm (KLRA),
6) Weighted Random Multiple Switch Algorithm (WRMSA),
7) Weighted Greedy Multiple Switch Algorithm (WGMSA).
Our experiments were conducted on all completely unimodal
four-dimensional hypercubes and on randomly generated
hypercubes of dimensions up to sixteen, Hamiltonian
(presumably corresponding to hard problem instances) and
non-Hamiltonian.
Local-search improvement algorithms 1 and 2 have been
investigated earlier, but number 3, 4, 5, 6, and 7 probably
not. Algorithm 5 (first time used for completely unimodal
hypercubes in this paper) is the only algorithm with the
known \emph{subexponential} expected worst-case running
time. However, the algorithms 1, 3, 4, 6, 7 demonstrate
superior behaviors compared to the other two investigated
algorithms. This suggests that further theoretical and
experimental studies of these algorithms should be carried
out. }
}
@TechReport{ it:2001-016,
author = {Robert Stjernstr{\"o}m},
title = {User-Centred Design of a Train Driver Display},
institution = it,
department = hci,
year = 2001,
number = {2001-016},
month = aug,
note = {M.Sc. thesis},
abstract = {This paper describes how a graphical user interface was
developed in the TRAIN Project at the Department of
Information Technology at Uppsala University.
The TRAIN Project was initiated by The Board of Accident
Investigation due to the commuter train accident in
{\"A}lvsj{\"o} in 1994. The Swedish National Rail
Administration was assigned to fund and manage the project,
while independent researchers where assigned to carry out
the research.
One objective has been to investigate how the future work
environment for train drivers can be improved. To
accomplish this, requirements have been collected using
user-centred design with rapid prototyping in Java and XML.
Another objective has been to introduce user-centred design
as an advantageous method for further development of the
graphical user interface
The result is a prototype containing most of the
requirements from the drivers in the work group. The
prototype is interactive and simulates the real behaviour
of a train - acceleration, retardation and the train track
are modelled according to reality.
The conclusions are that the prototype can be used by train
drivers to refine the requirements of the system even
further.
Furthermore, the prototype can be used to give management a
deeper understanding of what type of system the users
require and an implication that the user-centred design can
be favorably employed in future work.}
}
@TechReport{ it:2001-015,
author = {Magnus Sv{\"a}rd},
title = {On coordinate transformations for summation-by-parts
operators},
institution = it,
department = tdb,
year = 2001,
number = {2001-015},
month = aug,
abstract = {High order finite difference methods obeying a
summation-by-parts (SBP) rule are developed for equidistant
grids. With curvilinear grids, a coordinate transformation
operator that does not destroy the SBP property must be
used. We show that it is impossible to construct such an
operator without decreasing the order of accuracy of the
method. }
}
@TechReport{ it:2001-014,
author = {Paul Pettersson and Sergio Yovine},
title = {Workshop on Real-Time Tools (Proceedings)},
institution = it,
department = docs,
year = 2001,
number = {2001-014},
address = {Aalborg University, Denmark},
month = aug
}
@TechReport{ it:2001-013,
author = {Eva Olsson and Lena Kecklund and Michael Ingre and Anders
Jansson},
title = {Lokf{\"o}rarens informationsmilj{\"o} och {ATC}. Ett
anv{\"a}ndarperspektiv},
institution = it,
department = hci,
year = 2001,
number = {2001-013},
month = jun,
note = {In Swedish},
abstract = {Syftet med TRAIN-projektet var att utv{\"a}rdera de
trafiks{\"a}kerhetsm{\"a}ssiga effekterna av f{\"o}rarens
informationsmilj{\"o} och arbetssituation. I denna rapport
redovisas resultaten fr{\aa}n den enk{\"a}tunders{\"o}kning
som under h{\"o}sten 1999 som unders{\"o}kte
lokf{\"o}rarens informationsmilj{\"o} med s{\"a}rskilt
fokus p{\aa} anv{\"a}ndningen av ATC-systemet. En
sammanfattande bild av lokf{\"o}rarens arbete visar att en
viktig uppgift {\"a}r att samla in och integrera
information fr{\aa}n olika informationsk{\"a}llor f{\"o}r
en s{\"a}ker och punktlig k{\"o}rning. ATC {\"a}r en viktig
informationsk{\"a}lla vid k{\"o}rning av b{\aa}de
pendelt{\aa}g och X2. Var man h{\"a}mtar sin information
beror i viss utstr{\"a}ckning p{\aa} fordon och typ av
arbetsuppgift. F{\"o}rarna ans{\aa}g att ATC var ett mycket
viktigt hj{\"a}lpmedel och st{\"o}d i k{\"o}rningen
s{\"a}rskilt under perioder av tr{\"o}tthet och
f{\"o}rs{\"a}mrad uppm{\"a}rksamhet. Det fanns dock en del
brister med avseende p{\aa} hur ATC presenterar
information, hur olika funktioner i ATC utformats samt hur
f{\"o}raren och ATC-systemet samverkar. Den
trafiks{\"a}kerhetsm{\"a}ssiga p{\aa}verkan av dessa
f{\"o}rh{\aa}llanden kommenteras i rapporten. Sammantaget
kan man dock konstatera att inf{\"o}randet av ATC i Sverige
inneburit en v{\"a}sentlig {\"o}kning av trafiks{\"a}kerhetsniv{\aa}n. }
}
@TechReport{ it:2001-012,
author = {Friedhelm Stappert and Andreas Ermedahl and Jakob
Engblom},
title = {Efficient Longest Executable Path Search for Programs with
Complex Flows and Pipeline Effects},
institution = it,
department = docs,
year = 2001,
number = {2001-012},
month = jun,
abstract = {Knowing the Worst-Case Execution Time (WCET) of a program
is necessary when designing and verifying real-time
systems. A correct WCET calculation method must take into
account the possible program flow, like loop iterations and
function calls, as well as effects of hardware features,
like caches and pipelines.
In this paper we describe our work on calculating the WCET
of programs with complex flow information using a
path-based approach, and on how pipeline information can be
efficiently included in the calculation. The result is a
set of algorithms that allows for efficient and precise
calculation of the WCET of programs with more complex flows
and pipeline effects than was previously possible.
This technical report is an extended version of the
conference submission.}
}
@TechReport{ it:2001-011,
author = {Torsten S{\"o}derstr{\"o}m and Umberto Soverini and
Kaushik Mahata},
title = {Perspectives on errors-in-variables estimation for dynamic
systems},
institution = it,
department = syscon,
year = 2001,
number = {2001-011},
month = may,
abstract = {The paper gives an overview of various methods for
identifying dynamic errors-in-variables systems. Several
approaches are classified by how the original information
in time-series data of the noisy input and output
measurements is condensed before further processing. For
some methods, such as instrumental variable estimators, the
information is condensed into a nonsymmetric covariance
matrix as a first step before further processing. In a
second class of methods, where a symmetric covariance
matrix is used instead, the Frisch scheme and other
bias-compensation approaches appear. When dealing with the
estimation problem in the frequency domain, a milder data
reduction typically takes place by first computing spectral
estimators of the noisy input-output data. Finally, it is
also possible to apply maximum likelihood and prediction
error approaches using the original time-domain data in a
direct fashion. This alternative will often require quite
high computational complexity but yield good statistical
efficiency.
The paper is also presenting various properties of
parameter estimators for the errors-in-variables problem,
and a few conjectures are included, as well as some
perspectives and experiences by the authors. }
}
@TechReport{ it:2001-010,
author = {Thiemo Voigt and Per Gunningberg},
title = {Dealing with Memory-Intensive Web Requests},
institution = it,
department = docs,
year = 2001,
number = {2001-010},
month = may,
abstract = {Web servers must be protected from overload since server
overload can lead to low throughput and high, unpredictable
response times. In this paper we present a new admission
control architecture that prevents server overload caused
by high paging rates. The main idea of our admission
control scheme is to delay the processing of requests when
there is high memory pressure. We present experiments that
show that our admission control architecture sustains high
throughput even during a flash crowd of memory-intensive
requests. }
}
@TechReport{ it:2001-009,
author = {Johan Bengtsson},
title = {Reducing Memory Usage in Symbolic State-Space Exploration
for Timed Systems},
institution = it,
department = docs,
year = 2001,
number = {2001-009},
month = may,
abstract = {One of the major problems when applying model checkers to
industrial-size system is the large memory consumption.
This report address the problem in the context of verifiers
for timed systems and present a number of techniques that
reduce the amount memory used for state space exploration
in such a tool. The methods are evaluated and compared by
real-life examples and their strengths and weaknesses are
described.
In particular we adress the memory consumption problem on
two fronts, first by reducing the size of each symbolic
state by means of compression and second by reducing the
size of the stored state space by early inclusion checking
and probabilistic methods. }
}
@TechReport{ it:2001-008,
author = {Viktor Petersson and Sergei Vorobyov},
title = {Parity Games: Interior-Point Approach},
institution = it,
department = csd,
year = 2001,
number = {2001-008},
month = may,
abstract = {We introduce and investigate continuous optimization
techniques for solving \textsc{Parity Games}, based on the
\emph{interior-point paradigm}, combining barrier functions
and quasi-Newton methods. These have been proven very
successful for \textsc{Linear and Convex Programming}. The
basic step is to leave the boundary (i.e. the stationary
strategies in which such games can be solved) and to cut
through the interior (i.e. probabilistic strategies) of the
many-dimensional hypercube of strategies. }
}
@TechReport{ it:2001-007,
author = {Sven Montan},
title = {Validation of Cycle-Accurate {CPU} Simulators against Real
Hardware},
institution = it,
department = docs,
year = 2001,
number = {2001-007},
month = apr,
note = {M.Sc. thesis},
abstract = {One of the most important issues regarding real-time
software performance is the worst case execution time
(WCET). There are several methods for deducing the WCET
statically; one such analysis system is currently under
development by WCET researchers from Uppsala University in
co-operation with C-lab in Paderborn. The system uses a CPU
simulator for calculating the execution time of selected
parts of the target program, which creates a demand for a
very cycle-accurate simulator.
In this thesis, we give a method for validating a CPU
simulator against real hardware CPU. The proposed test
method is a black-box test method that relies on hardware
analysis for test-case generation. The validation method
aims at both determining the accuracy of the simulator and
to pinpoint simulator errors for improving the accuracy.
We have tested this validation method on a NEC V850 CPU
core simulator, and the results show that the average
error-rate drops from 11,2\% to 1,3\% for a set of
benchmark programs. }
}
@TechReport{ it:2001-006,
author = {Erik K. Larsson and Torsten S{\"o}derstr{\"o}m},
title = {Identification of Continuous-Time {AR} Processes by Using
Limiting Properties of Sampled Systems},
institution = it,
department = syscon,
year = 2001,
number = {2001-006},
month = mar,
abstract = {Consider the problem of estimating the parameters in a
continuous-time autoregressive (CAR) model from
discrete-time samples. In this paper a simple and
computationally efficient method is introduced, and
analyzed with respect to bias distribution. The approach is
based on replacing the derivatives by delta approximations,
forming a linear regression, and using the least squares
method. It turns out that consistency can be assured by
applying a particular prefilter to the data; a filter that
is easy to compute and is only dependent on the order of
the continuous-time system. As a side effect several
general properties for discrete-time autoregressive moving
average (ARMA) systems originating from sampled
CAR-processes will also be presented. Finally, the
introduced method is compared to other methods in some
simulation studies. }
}
@TechReport{ it:2001-005,
author = {Yordanos G. Beyene},
title = {Firewalls in {L}inux: Principles and Implementation},
institution = it,
department = docs,
year = 2001,
number = {2001-005},
month = feb,
note = {M.Sc. thesis},
abstract = {This paper is meant to provide techniques in building and
installing a standalone packet filtering firewall in Linux
machines, mainly for small sites who don't give much
service to Internet users. It deals with attenuating the
effect of the most common types of attacks using ipchains.
It guides how to design, implement, debug, and maintain
Firewall. Techniques for continuously monitoring attacks is
attempted. It also give a historical, architectural and
technical overview of firewalls and security attacks. }
}
@TechReport{ it:2001-004,
author = {Bernhard M{\"u}ller and H.C. Yee},
title = {High Order Numerical Simulation of Sound Generated by the
{K}irchhoff Vortex},
institution = it,
department = tdb,
year = 2001,
number = {2001-004},
month = feb,
note = {Published as RIACS Technical Report 01.02, Jan. 2001, NASA
Ames Research Center, and submitted to Computing and
Visualization in Science},
abstract = {An improved high order finite difference method for low
Mach number computational aeroacoustics (CAA) is described.
The improvements involve the conditioning of the Euler
equations to minimize numerical cancellation errors, and
the use of a stable non-dissipative sixth-order central
spatial interior scheme and a third-order boundary scheme.
Spurious high frequency oscillations are damped by a
third-order characteristic-based filter. The objective of
this paper is to apply these improvements in the simulation
of sound generated by the Kirchhoff vortex. }
}
@TechReport{ it:2001-003,
author = {Karl H{\"o}rnell and Per L{\"o}tstedt},
title = {Adaptive Iteration to Steady State of Flow Problems},
institution = it,
department = tdb,
year = 2001,
number = {2001-003},
month = feb,
abstract = {Runge-Kutta time integration is used to reach the steady
state solution of discretized partial differential
equations. Continuous and discrete parameters in the method
are adapted to the particular problem by minimizing the
residual in each step, if this is possible. Algorithms for
parameter optimization are devised and analyzed. Solutions
of the nonlinear Euler and Navier-Stokes equations for
compressible flow illustrate the methods.}
}
@TechReport{ it:2001-002,
author = {Johan Steensland},
title = {Dynamic Structured Grid Hierarchy Partitioners Using
Inverse Space-Filling Curves},
institution = it,
department = tdb,
year = 2001,
number = {2001-002},
month = feb,
abstract = {This paper discusses partitioning of dynamic structured
grid hierarchies, occuring in structured adaptive mesh
refinement (SAMR) applications. When a SAMR method is
executed on a parallel computer, the work load will change
dynamically. Thus, there is need for dynamic load
balancing. Inverse space-filling curve partitioning (ISP)
is appealing for load balancing in parallel SAMR, because
of its speed. In this paper, ISP is considered as
\textit{part} of a partitioning approach, which combines
structured and unstructured techniques. More precisely,
various design decisions for the structured partitioning
are considered. Different design choices lead to graphs
with different properties. The main objective is to
investigate how these differences affect the behavior of
ISP. The paper contributes by (a)~identifying certain
design choices as being advantageous, and (b) presenting
four new partitioning algorithms that correspond to these
design decisions. }
}
@TechReport{ it:2001-001,
author = {Viktor Petersson and Sergei Vorobyov},
title = {A Randomized Subexponential Algorithm for Parity Games},
institution = it,
department = csd,
year = 2001,
number = {2001-001},
month = jan,
abstract = {We describe a randomized algorithm for \textsc{Parity
Games} (equivalent to the \textsc{Mu-Calculus Model
Checking}), which runs in expected time
$2^{O(k^{1/(1+2\varepsilon)})}$ \emph{subexponential} in
the number of colors $k$ of the game graph when $k$ is
$\Omega(n^{1/2+\varepsilon})$, $n$ is the number of
vertices, and $0<\varepsilon\leq 1/2$.
All previously known algorithms were \emph{exponential} in
the number of colors, with the best one taking time and
space $O(k^2\cdot n\cdot \sqrt{n}^k)$.
Our algorithm does not rely on Linear Programming
subroutines and uses a low-degree polynomial space. }
}
@TechReport{ it:2000-035,
author = {Henrik Brand{\'e}n and Sverker Holmgren},
title = {Convergence acceleration for the steady state {E}uler
equations},
institution = it,
department = tdb,
year = 2000,
number = {2000-035},
month = dec,
abstract = {We consider the iterative solution of systems of equations
arising from discretizations of the non-linear Euler
equations governing compressible flow. The differential
equation is discretized on a structured grid, and the
steady state solution is computed by a time-marching method.
A convergence acceleration technique based on semicirculant
approximations of the difference operator or the Jacobian
is used. Implementation issues and variants of the scheme
allowing for a reduction of the arithmetic complexity and
memory requirement are discussed. The technique can be
combined with a variety of iterative solvers, but we focus
on non-linear explicit Runge-Kutta time-integration
schemes. The results show that the single-stage forward
Euler method can be used, and the time step is not limited
by a CFL-criterion. Instead it can be chosen as a constant,
independent of the number of grid points. This results in
that the arithmetic work required for computing the
solution is equivalent to the work required for a fixed
number of residual evaluations.
Two major advantages of the semicirculant convergence
acceleration technique is that it contains few tunable
parameters, and that it is robust with respect to the
amount of artificial viscosity used in the discretization.
}
}
@TechReport{ it:2000-034,
author = {Alexander Shen},
title = {Algorithmic Information Theory and Kolmogorov Complexity},
institution = it # {, and Independent University of Moscow, Russia},
department = csd,
year = 2000,
number = {2000-034},
month = dec,
abstract = {This document contains lecture notes of an introductory
course on Kolmogorov complexity. They cover basic notions
of algorithmic information theory: Kolmogorov complexity
(plain, conditional, prefix), notion of randomness
(Martin-Lof randomness, Mises-Church randomness),
Solomonoff universal a priori probability and their
properties (symmetry of information, connection between a
priori probability and prefix complexity, criterion of
randomness in terms of complexity) and applications
(incompressibility method in computational complexity
theory, incompleteness theorems). }
}
@TechReport{ it:2000-033,
author = {Olsson, Eva and Sandblad, Bengt and Kecklund, Lena},
title = {S{\"a}kerhetssamtal. Nul{\"a}ge och f{\"o}r{\"a}ndringsbehov},
institution = it,
department = hci,
year = 2000,
number = {2000-033},
month = dec,
note = {In Swedish},
abstract = {Denna rapport {\"a}r en sammanst{\"a}llning av fr{\aa}gor
som r{\"o}r kommunikationen mellan f{\"o}rare och
t{\aa}gtrafikstyrning, s{\aa} kallade samtal i
s{\"a}kerhetstj{\"a}nst. Intervjuer med sju f{\"o}rare
fr{\aa}n Hagalund som gjorts inom ramen f{\"o}r projektet
\emph{TRAIN} (Trafiks{\"a}kerhet och informationsmilj{\"o}
f{\"o}r t{\aa}gf{\"o}rare) under december 1999 utg{\"o}r
underlag f{\"o}r de synpunkter p{\aa} s{\"a}kerhetssamtal
som kommer fr{\aa}n f{\"o}rare. P{\aa} motsvarande s{\"a}tt
har ett antal intervjuer med t{\aa}gledare vid flera
trafikledningscentraler tidigare genomf{\"o}rts inom ramen
f{\"o}r forskningsprojektet \emph{Framtida
t{\aa}gtrafikstyrning}. Inom det projektet har dessutom en
arbetsgrupp under en serie m{\"o}ten bl.a. diskuterat hur
man ser p{\aa} dagens s{\"a}kerhetssamtal, och p{\aa} de
framtida f{\"o}r{\"a}ndringar som man ser som
{\"o}nskv{\"a}rda. Resultat fr{\aa}n dessa diskussioner
presenteras ocks{\aa} relativt utf{\"o}rligt h{\"a}r i form
av mer framskridna f{\"o}rslag till
kommunikationsl{\"o}sningar. Det framkommer p{\aa} olika
s{\"a}tt, b{\aa}de i diskussioner med lokf{\"o}rare och med
t{\aa}gledare, att man upplever brister i det s{\"a}tt man
samverkar och kommunicerar. Bristerna har olika anledning.
Det finns tekniska sv{\aa}righeter och sv{\aa}righeter som
ligger i kunskap, organisation och rutiner. Det framkommer
ocks{\aa} tydligt att man till stor del saknar information
och kunskap om varandras arbete. Detta g{\"o}r det
sv{\aa}rare att f{\"o}rst{\aa} varandras arbetsrelaterade
problem och att veta vilken information som man skulle
kunna l{\"a}mna f{\"o}r att f{\"o}rb{\"a}ttra varandras
m{\"o}jligheter att prestera bra. Man saknar ofta
information och beslutsunderlag under arbetsprocesserna.
Detta leder till att man agerar utg{\aa}ende fr{\aa}n den
begr{\"a}nsade information man har samt att man {\"a}r
tvungen att g{\"o}ra bed{\"o}mningar av den r{\aa}dande
situationen. F{\"o}rb{\"a}ttrad information presenterad
p{\aa} ett s{\"a}tt som st{\"o}djer f{\"o}raren i arbetet
kan ge varje enskild lokf{\"o}rare den {\"o}verblick av den
aktuella och kommande situationen som bidrar till att
trafikfl{\"o}det optimeras. Informationen skulle inte bara
{\"o}ka s{\"a}kerheten, den skulle ocks{\aa} kunna medverka
till mindre stress och mer planerad k{\"o}rning f{\"o}r
lokf{\"o}rarna. P{\aa} samma s{\"a}tt skulle situationen
f{\"o}r t{\aa}gledarna kunna f{\"o}rb{\"a}ttras om dessa
hade mer information om f{\"o}rh{\aa}llandena som
g{\"a}ller f{\"o}r lokf{\"o}rarna, vad som sker med loken
och t{\aa}gen som har inverkan p{\aa} trafiken, eventuella
st{\"o}rningar m.m. Man skulle d{\aa} kunna planera
trafiken utifr{\aa}n mer aktuell och fullst{\"a}ndig
information, kunna f{\"o}ruts{\"a}ga kommande
st{\"o}rningar och konflikter i trafiken. Detta skulle leda
till b{\"a}ttre s{\"a}kerhet, effektivare trafikf{\"o}ring och ett lugnare arbete p{\aa} trafikledningscentralen. }
}
@TechReport{ it:2000-032,
author = {Henrik Brand{\'e}n and Per Sundqvist},
title = {Preconditioners Based on Fundamental Solutions},
institution = it,
department = tdb,
year = 2000,
number = {2000-032},
month = nov,
note = {Revised version available as IT technical report
2005-001},
abstract = {We consider a new convergence acceleration technique for
the iterative solution of linear systems of equations that
arise when discretizing partial differential equations. The
method is applied to finite difference discretizations, but
the ideas and the basic theory apply to other
discretizations too.
If $E$ is a fundamental solution of a differential operator
$P$, we have \mbox{$E\ast(Pu)=u$.} Inspired by this, we
choose the preconditioner to be a discretization of the
approximative inverse $K$, given by \[
(Ku)(x)=\int_{\Omega}E(x-y)u(y)dy, \qquad
x\in\Omega\subset\mathds{R}^d, \] where $\Omega$ is the
domain of interest. The operator $K$ is only an
approximation of $P^{-1}$ since we do not integrate over
all of $\mathds{R}^d$ as for the convolution, and since we
impose boundary conditions. Two main advantages of this
method are that we can perform analysis before we
discretize the operators, and that there is a fast way of
applying the preconditioner using FFT.
We present analysis showing that if $P$ is a first order
differential operator, $KP$ is bounded. The analysis also
describes how $K$ differs from $P^{-1}$. Implementation
aspects are considered, and numerical results show grid
independent convergence for first order partial
differential equations. For the second order
convection-diffusion equation convergence is no longer grid
independent, a result that is consistent with our theory.
However, if the grid is chosen to give a fixed number of
grid points within boundary layers, the number of
iterations is independent of the physical viscosity parameter. }
}
@TechReport{ it:2000-031,
author = {Anders Jansson and Eva Olsson and Lena Kecklund},
title = {Att k{\"o}ra t{\aa}g},
institution = it,
department = hci,
year = 2000,
number = {2000-031},
month = nov,
note = {In Swedish}
}
@TechReport{ it:2000-030,
author = {Richard Carlsson and Bj{\"o}rn Gustavsson and Erik
Johansson and Thomas Lindgren and Sven-Olof Nystr{\"o}m and
Mikael Pettersson and Robert Virding},
title = {Core {E}rlang 1.0 language specification},
institution = it,
department = csd,
year = 2000,
number = {2000-030},
month = nov,
abstract = {We describe a core language for the concurrent functional
language Erlang, aptly named ``Core Erlang'', presenting
its grammar and informal static and dynamic semantics
relative to Erlang. We also discuss built-in functions and
other open issues, and sketch a syntax tree
representation.}
}
@TechReport{ it:2000-029,
author = {Mikael Pettersson},
title = {A staged tag scheme for {E}rlang},
institution = it,
department = csd,
year = 2000,
number = {2000-029},
month = nov,
abstract = {The runtime systems in Ericsson's implementations of the
Erlang programming language, up to and including release
R6B, use a simple tag scheme which allows for fast
computation of an object's type. However, the tag scheme
also restricts all Erlang objects to a 28- or 30-bit
address space. This is problematic when Erlang is ported to
new systems, and reduces reliability for applications
needing large amounts of memory.
This paper describes the development of a new \emph{staged}
tag scheme, which was designed to \emph{not} restrict the
range of pointers, and thus eliminate the source of the
abovementioned problems. Secondary benefits also followed:
the staged tag scheme is more flexible, and, perhaps
surprisingly, is actually more efficient.
The staged tag scheme has been integrated into Ericsson's
Erlang code, and is a standard feature starting with
release R7A. }
}
@TechReport{ it:2000-028,
author = {Bharath Bhikkaji and Torsten S{\"o}derstr{\"o}m},
title = {Reduced order models for diffusion systems using singular
perturbations},
institution = it,
department = syscon,
year = 2000,
number = {2000-028},
month = nov,
abstract = {In this paper, we consider a special case of the one
dimensional heat diffusion across a homogeneous wall. This
physical system is modeled by a linear partial differential
equation, which can be thought of as an infinite
dimensional dynamic system. To simulate this physical
system, one has to approximate the underlying infinite
order system by a finite order approximation. In this paper
we first construct a simple and straightforward approximate
finite order model for the true system. The proposed
approximate models may require large model order to
approximate the true system dynamics in the high frequency
regions. To avoid the usage of higher order models, we use
a scheme similar to singular perturbations to further
reduce the model order. }
}
@TechReport{ it:2000-027,
author = {Emad Abd-Elrady},
title = {Convergence of the {RPEM} as Applied to Harmonic Signal
Modeling},
institution = it,
department = syscon,
year = 2000,
number = {2000-027},
month = oct,
abstract = {Arbitrary periodic signals can be estimated recursively by
exploiting the fact that a sine wave passing through a
static nonlinear function generates a spectrum of
overtones. The estimated signal model is hence
parameterized as a real wave with unknown period in cascade
with a piecewise linear function. The driving periodic wave
can be chosen depending on any prior knowledge. The
performance of a recursive Gauss-Newton prediction error
identification algorithm for joint estimation of the
driving frequency and the parameters of the nonlinear
output function is therefore studied. A theoretical
analysis of local convergence to the true parameter vector
as well as numerical examples are given. Furthermore, the
Cramer-Rao bound (CRB) is calculated in this report. }
}
@TechReport{ it:2000-026,
author = {Henrik Brand{\'e}n},
title = {Numerical Boundary Conditions for {ODE}},
institution = it,
department = tdb,
year = 2000,
number = {2000-026},
month = oct,
optnote = {Submitted to Numerische Mathematik},
abstract = {We consider consistent finite difference approximations of
ordinary differential equations, and in particular,
parasitic solutions. A framework is introduced,
representing a discrete solution as a sum of the true
solution and a number of parasitic solutions. We show that
within this framework, finite difference equations can be
analysed using theory of ordinary differential equations,
simplifying the analysis considerably. As an example we
give a simple recipe on how to construct numerical boundary
conditions such that the solution converges with expected
accuracy.}
}
@TechReport{ it:2000-025,
author = {Huimin Lin and Wang Yi},
title = {A Complete Axiomatisation for Timed Automata},
institution = it,
department = docs,
year = 2000,
number = {2000-025},
month = sep,
note = {A short version of this paper will be included in the
proceedings of 20th FST-TCS, 2000},
abstract = {Timed automata has been recognised as a fundamental model
for real time systems, but it still lacks a satisfactory
algebraic theory. This paper fills the gape by presenting a
complete proof system for timed automata, in which the
equalities between pairs of timed automata that are timed
bisimilar can be derived. The proof of the completeness
result relies on the introduction of the notion of symbolic
timed bisimulation. }
}
@TechReport{ it:2000-024,
author = {Saul Abarbanel and Adi Ditkowski and Bertil Gustafsson},
title = {On error bounds of finite difference approximations to
partial differential equations - temporal behavior and rate
of convergence},
institution = it,
department = tdb,
year = 2000,
number = {2000-024},
month = sep,
abstract = {This paper considers a family of spatially semi-discrete
approximations, including boundary treatments, to
hyperbolic and parabolic equations. We derive the
dependence of the error-bounds on time as well as on mesh
size.}
}
@TechReport{ it:2000-023,
author = {Per L{\"o}tstedt and Stefan S{\"o}derberg and Alison
Ramage and Lina Hemmingsson-Fr{\"a}nd{\'e}n},
title = {Implicit solution of hyperbolic equations with space-time
adaptivity},
institution = it,
department = tdb,
year = 2000,
number = {2000-023},
month = sep,
abstract = {Adaptivity in space and time is introduced to control the
error in the numerical solution of hyperbolic partial
differential equations. The equations are discretised by a
finite volume method in space and an implicit linear
multistep method in time. The computational grid is refined
in blocks. At the boundaries of the blocks, there may be
jumps in the step size. Special treatment is needed there
to ensure second order accuracy and stability. The local
truncation error of the discretisation is estimated and is
controlled by changing the step size and the time step. The
global error is obtained by integration of the error
equations. In the implicit scheme, the system of linear
equations at each time step is solved iteratively by the
GMRES method. Numerical examples executed on a parallel
computer illustrate the method. }
}
@TechReport{ it:2000-022,
author = {Johan Runeson and Sven-Olof Nystr{\"o}m and Jan Sj{\"o}din},
title = {Optimizing Code Size through Procedural Abstraction},
institution = it,
department = csd,
year = 2000,
number = {2000-022},
month = sep,
note = {An extended abstract appears in the Proceedings of the ACM
SIGPLAN 2000 Workshop on Languages, Compilers, and Tools
for Embedded Systems (LCTES'2000)},
abstract = {Memory size is an important economic factor in the
development of embedded systems. It is therefore desirable
to find compiler optimization techniques that reduce the
size of the generated code. One such code compression
technique is procedural abstraction, where repeated
occurrences of equivalent code fragments are factored out
into new subroutines. Previously, procedural abstraction
has been applied at the machine code level in optimizing
linkers or binary rewriting tools. We investigate the
prospects of applying procedural abstraction at the
intermediate code level of a whole-program optimizing C
compiler. Placing the optimization before register
allocation makes it target independent, and will allow us
to take full advantage of powerful code selection, register
allocation and code scheduling techniques. }
}
@TechReport{ it:2000-021,
author = {Parosh Aziz Abdulla and Aletta Nyl{\'e}n},
title = {{BQO}s and Timed Petri Nets},
institution = it,
department = docs,
year = 2000,
number = {2000-021},
month = aug,
abstract = {In this paper, we use the theory of better quasi-orderings
to define a methodology for inventing constraint systems
which are both well quasi-ordered and compact. We apply our
methodology by presenting new constraint systems for
verification of systems with unboundedly many real-valued
clocks, and use them for checking safety properties for
lazy (non-urgent) timed Petri nets where each token is
equipped with a real-valued clock.}
}
@TechReport{ it:2000-020,
author = {Karl H{\"o}rnell and Per L{\"o}tstedt},
title = {Time step selection for shock problems},
institution = it,
department = tdb,
year = 2000,
number = {2000-020},
month = aug,
abstract = {The solution to a conservation law is integrated in time
by an embedded Runge-Kutta method. The time steps are
chosen so that a bound on the local error is satisfied. At
discontinuities such as shocks in the solution the time
step is too pessimistic. By filtering the error estimate
the time steps are determined by the smooth parts of the
solution. The technique is justified theoretically and in
numerical experiments. }
}
@TechReport{ it:2000-019,
author = {Torsten S{\"o}derstr{\"o}m and Bharath Bhikkaji},
title = {Reduced order models for diffusion systems},
institution = it,
department = syscon,
year = 2000,
number = {2000-019},
month = aug,
abstract = {Mathematical models for diffusion processes like heat
propagation, dispersion of pollutants etc., are normally
partial differential equations which involve certain
unknown parameters. To use these mathematical models as the
substitutes of the true system, one has to determine these
parameters.
Partial differential equations (PDE) of the form \bea
\frac{\partial u(x,t)}{\partial t} = \mathcal{L} u(x,t)
\label{eq1.1} \eea where $ \mathcal{L}$ is a linear
differential (spatial) operator, describe infinite
dimensional dynamical systems. To compute a numerical
solution for such partial differential equations, one has
to approximate the underlying system by a finite order one.
By using this finite order approximation, one then computes
an approximate numerical solution for the PDE.
We consider a simple case of heat propagation in a
homogeneous wall. The resulting partial differential
equation, which is of the form (\ref{eq1.1}), is
approximated by finite order models by using certain
existing numerical techniques like Galerkin and Collocation
etc. These reduced order models are used to estimate the
unknown parameters involved in the PDE, by using the well
developed tools of system identification.
In this paper we concentrate more on the model reduction
aspects of the problem. In particular, we examine the model
order reduction capabilities of the Chebyshev polynomial
methods used for solving partial differential equation. }
}
@TechReport{ it:2000-018,
author = {Torsten S{\"o}derstr{\"o}m and Bharath Bhikkaji},
title = {Reduced order models for diffusion systems via collocation
methods},
institution = it,
department = syscon,
year = 2000,
number = {2000-018},
month = aug,
abstract = {Mathematical models for diffusion processes like heat
propagation, dispersion of pollutants etc., are normally
partial differential equations involving unknown
parameters. For practical use, one has to estimate these
parameters. In this paper we consider a simple case of heat
propagation in a homogeneous wall. The resulting partial
differential equation is solved using numerical techniques
and tools of system identification are used to estimate the
unknown parameters. In particular we examine the effect of
model order selection when a Chebyshev collocation method
is applied for solving partial differential equations. }
}
@TechReport{ it:2000-017,
author = {Arne Andersson and Per Carlsson and Fredrik Ygge},
title = {Resource Allocation With Noisy Functions},
institution = it,
department = csd,
year = 2000,
number = {2000-017},
month = aug,
abstract = {We consider resource allocation with separable objective
functions defined over subranges of the integers. While it
is well known that (the maximisation version of) this
problem can be solved efficiently if the objective
functions are concave, the general problem of resource
allocation with functions that are not necessarily concave
is difficult.
In this article we show that for a large class of problem
instances with noisy objective functions the optimal
solutions can be computed efficiently. We support our
claims by experimental evidence. Our experiments show that
our algorithm in hard and practically relevant cases runs
up to 40 - 60 times faster than the brute force testing of
all possible solutions. }
}
@TechReport{ it:2000-016,
author = {Ken Mattsson},
title = {Imposing Boundary Conditions with the Injection, the
Projection and the Simultaneous Approximation Term Method},
institution = it,
department = tdb,
year = 2000,
number = {2000-016},
month = jul,
abstract = {Four different methods of imposing boundary conditions for
the linear advection-diffusion equation and a linear
hyperbolic system are considered. The methods are analyzed
using the energy method and the Laplace transform
technique. Numerical calculations are done, considering in
particular the case when the initial data and boundary data
are inconsistent. }
}
@TechReport{ it:2000-015,
author = {Petre Stoica and Girish Ganesan},
title = {On a Parameter Estimation Algorithm for {MA} Time
Series.},
institution = it,
department = syscon,
year = 2000,
number = {2000-015},
month = jun,
abstract = {We take a close look at an algorithm for MA(1) parameter
estimation. We provide a thorough convergence analysis of
that algorithm in the scalar case, discuss its main
advantages and disadvantages, present a possible extension
of it to the MA($n$) case, and compare it with a recent
alternative algorithm that appears to be one of the best
available choices for MA parameter estimation.}
}
@TechReport{ it:2000-014,
author = {Sergei Vorobyov},
title = {Better Decision Algorithms for Parity Games and the
Mu-Calculus Model Checking},
institution = it,
department = csd,
year = 2000,
number = {2000-014},
month = jun,
abstract = {We suggest an algorithm with the asymptotically best
behavior among currently known algorithms for the problems
enumerated in the title, when the number of alternations
$k$ is $\Omega(n^{\frac{1}{2}+\varepsilon})$, where $n$ is
the number of states and $0<\varepsilon\leq\frac{1}{2}$.
The best previously known algorithm
\cite{BrowneClarkeJhaLongMarrero97} runs in time
$O(k^2\cdot n\cdot \sqrt{n}^k)$ and uses approximately the
same space. For comparison, our algorithm for $k=n$ (the
most difficult case) runs in time $O(n^3\cdot (1.61803)^k)$
and uses a small polynomial space. We also show, for the
first time, that there is a \emph{subexponential}
randomized algorithms for the problem when
$k=\Omega(n^{\frac{1}{2}+\varepsilon})$. It was an open
problem as to whether such algorithms exist at all. }
}
@TechReport{ it:2000-013,
author = {Marcus Johansson},
title = {Loss of High Order Spatial Accuracy Due to Boundary Error
Caused by Runge-Kutta Time Integration},
institution = it,
department = tdb,
year = 2000,
number = {2000-013},
month = may,
abstract = {Explicit Runge--Kutta methods have frequently been used
for solving initial boundary value problems with the method
of lines. For linear and certain non-linear problems like
the inviscid Burgers' equation, the correct specification
of Dirichlet boundary conditions at the intermediate
Runge--Kutta stages can be derived analytically. For
general non-linear PDEs and general boundary conditions, it
is currently not known how to find consistent analytical
boundary conditions that do not lower the formal accuracy
of the scheme. There are some numerical approaches that
gain full accuracy but lead to deteriorated stability
conditions. Here we focus on solving non-linear wave like
equations using high-order finite difference methods. We
examine the properties of an inconsistent boundary
treatment and make comparisons with a correct one when
applicable. We examine the effect of introducing viscosity.
We contrast fourth order Runge--Kutta and Adams--Bashforth
time integrators.}
}
@TechReport{ it:2000-012,
author = {Maria Karlsson and Fredrik Ygge},
title = {Market-based Approaches to Optimization},
institution = it,
department = csd,
year = 2000,
number = {2000-012},
month = may,
abstract = {The use of markets has been proposed to a number of
resource allocation/optimization problems, as such
approaches often have a number of conceptual advantages.
However, most examples found in the literature are rather
ad hoc.
In this article we present a general definition of what
constitutes a market-oriented approach to optimization. We
demonstrate how this general framework can be used to
conceptually improve two well-known approaches from the
literature, and discuss computational properties of the
different approaches. We also present some general theory
and show that the theory of the two approaches under
investigation is special cases of this theory. }
}
@TechReport{ it:2000-011,
author = {Arne Andersson and Fredrik Ygge},
title = {Managing Large Scale Computational Markets},
institution = it,
department = csd,
year = 2000,
number = {2000-011},
month = apr,
abstract = {General equilibrium theory has been proposed for resource
allocation in computational markets. The basic procedure is
that agents submit bids and that a resource (re)allocation
is performed when a set of prices (one for each commodity)
is found such that supply meets demand for each commodity.
For successful implementation of large markets based on
general equilibrium theory, efficient algorithms for
finding the equilibrium are required. We discuss some
drawbacks of current algorithms for large scale equilibrium
markets and present a novel distributed algorithm, CoTree,
which deals with the most important problems. CoTree is
communication sparse, fast in adapting to preference
changes of a few agents, have minimal requirements on local
data, and is easy to implement. }
}
@TechReport{ it:2000-010,
author = {Jakob Carlstr{\"o}m},
title = {Efficient Approximation of Values in Gain scheduled
Routing},
institution = it,
department = docs,
year = 2000,
number = {2000-010},
month = apr,
abstract = {This paper shows how the cost of computation and memory of
a previously proposed routing algorithm can be reduced. The
routing algorithm, intended for communications networks
carrying multiple call classes, is based on gain scheduling
of precomputed relative value functions. Each relative
value function is computed by solving a reinforcement
learning problem, and defines a link admission control
policy. We propose a method for automatically selecting
points in a grid of per-class arrival intensities, for
which relative value functions are computed. After
construction of the grid, relative values are computed by
interpolation. The numerical studies of routing in a
network with two call classes show that less than 30
relative value functions are needed to avoid performance
degradation. }
}
@TechReport{ it:2000-009,
author = {Jakob Carlstr{\"o}m and Ernst Nordstr{\"o}m},
title = {Gain Scheduled Routing in Multi-Service Networks},
institution = it,
department = docs,
year = 2000,
number = {2000-009},
month = apr,
abstract = {This paper presents gain scheduled routing, a new scheme
for reward-maximization in multi-service loss networks.
Per-link control policies and their expected future rewards
are precomputed using Markov decision theory and stored in
lookup tables. Selection of appropriate table entries is
based on measured or predicted call arrival rates. An
approximation is introduced, which makes it possible to use
identical lookup tables on links having the same
capacities, although the links carry calls with different
link reward parameters. Simulations with Poisson arrival
processes show that gain scheduled routing offers
significant improvement of the average reward rate,
compared to least loaded path routing. Promising results
are also obtained in simulations with self-similar call
traffic. }
}
@TechReport{ it:2000-008,
author = {Jakob Carlstr{\"o}m},
title = {Predictive Gain Scheduling for Control of Self-Similar
Call Traffic in Broadband Networks},
institution = it,
department = docs,
year = 2000,
number = {2000-008},
month = apr,
abstract = {This paper presents and evaluates a gain scheduling
approach to solving the admission control and routing
problems for self-similar call arrival processes. The
control problem is decomposed into two sub-problems:
prediction of near-future call arrival rates and
computation of control policies for Poisson arrival
processes. At decision time, the predicted arrival rates
are used to select one of the control policies. The rate
predictions are made by neural networks, trained on-line,
and the control policies are computed using standard
techniques for Markov decision processes. In simulations,
this method achieves higher link utilization than methods
which do not exploit the memory of the arrival process. It
also adapts to the network traffic considerably faster than
a previously presented controller employing reinforcement
learning without decomposition of the problem. }
}
@TechReport{ it:2000-007,
author = {Lars Ferm and Per L{\"o}tstedt},
title = {On numerical errors in the boundary conditions of the
{E}uler equations},
institution = it,
department = tdb,
year = 2000,
number = {2000-007},
month = apr,
abstract = {Numerical errors in solution of the Euler equations of
fluid flow are studied. The error equations are solved to
analyze the propagation of the discretization errors. In
particular, the errors caused by the boundary conditions
and their propagation are investigated. Errors generated at
a wall are transported differently in subsonic and
supersonic flow. Accuracy may be lost due to the
accumulation of errors along walls. This can be avoided by
increasing the accuracy of the boundary conditions. Large
errors may still arise locally at the leading edge of a
wing profile. There, a fine grid is the best way to reduce
the error. }
}
@TechReport{ it:2000-006,
author = {Elisabeth Larsson and Sverker Holmgren},
title = {A Parallel Domain Decomposition Method for the {H}elmholtz
Equation},
institution = it,
department = tdb,
year = 2000,
number = {2000-006},
month = apr,
abstract = {A parallel solver for the Helmholtz equation in a domain
consisting of layers with different material properties is
presented. A fourth-order accurate finite difference
discretization is used. The arising system of equations is
solved with a preconditioned Krylov subspace method. A
domain decomposition framework is employed, where fast
transform subdomain preconditioners are used. Three ways of
treating the Schur complement of the preconditioner are
investigated, and the corresponding preconditioned
iterative methods are compared with a standard direct
method. It is noted that the convergence rate of the
iterative methods is closely related to how the Schur
complement system for the preconditioner is formed, and how
accurately it is solved. However, in almost all cases, the
gain in both memory requirements and arithmetic complexity
is large compared with the direct method. Furthermore, the
gain increases with problem size, allowing problems with
many unknowns to be solved efficiently. The efficiency is
further improved by parallelization using message-passing,
enabling us to solve even larger Helmholtz problems in less
time.}
}
@TechReport{ it:2000-005,
author = {P{\"a}r Samuelsson and Bengt Carlsson},
title = {Feedforward control of the external carbon flow rate in an
activated sludge process},
institution = it,
department = syscon,
year = 2000,
number = {2000-005},
month = mar,
note = {A short version will appear at the 1st World Congress of
the IWA, Paris 3-7 July 2000},
abstract = {Biological nitrogen removal in an activated sludge process
is obtained by two biological processes; nitrification and
denitrification. Denitrifying bacterias need sufficient
amounts of readily metabolized carbon. The objective of
this paper is to develop an automatic control strategy for
adjusting the external carbon flow rate so that the nitrate
concentration in the last anoxic compartment is kept at a
low pre-specified level. A simple model based feedforward
control combined with a standard feedback PI controller is
suggested. The feedforward part is based on a steady state
analysis of a simplified ASM1 model. Simulation results
show that the suggested controller, despite simple,
effectively attenuate process disturbances.}
}
@TechReport{ it:2000-004,
author = {Bengt G{\"o}ransson and Jan Gulliksen},
title = {Anv{\"a}ndarcentrerad systemutveckling},
institution = it,
department = hci,
year = 2000,
number = {2000-004},
month = mar,
note = {In Swedish. Also available as report TRITA-NA-D~0005,
CID-71, KTH, Stockholm, Sweden. An extended and revised
version is available in the book
\emph{Anv{\"a}ndarcentrerad systemdesign}, see
\url{http://acsd.hci.uu.se}},
abstract = {Denna rapport beskriver grunderna i anv{\"a}ndarcentrerad
systemutveckling och hur detta f{\"o}rh{\aa}ller sig till
ett antal systemutvecklingsmodeller. Den beskriver
anv{\"a}ndarmedverkan, projektstyrningsaspekter, metoder
och roller i arbetet. Den relaterar hela tiden till det
arbete som vi bedrivit tillsammans med Riksskatteverket och
rapporterar ocks{\aa} om ett antal observationer som gjorts
under de fem {\aa}r av samverkan med Riksskatteverket som
vi haft. S{\"a}rskild tonvikt har lagts p{\aa} att
anv{\"a}ndarmedverkan skall vara effektiv i
systemutvecklingsprocessen. Syftet med denna rapport {\"a}r
att f{\"o}rklara varf{\"o}r ett anv{\"a}ndarcentrerat
syns{\"a}tt {\"a}r n{\"o}dv{\"a}ndigt i organisationen, vad
man vinner p{\aa} detta och vilka fallgropar man skall
undvika. Det kan tj{\"a}na som ett underlag f{\"o}r att
bedriva ett anv{\"a}ndarcentrerat utvecklingsprojekt, men
ocks{\aa} som underlag/krav f{\"o}r upphandling av en
systemutvecklingsmodell och vad en s{\aa}dan modell b{\"o}r
kompletteras med f{\"o}r att bli anv{\"a}ndarcentrerad. Den
riktar sig till verksamhetsf{\"o}retr{\"a}dare och
it-strateger p{\aa} l{\aa}g som h{\"o}g niv{\aa}. }
}
@TechReport{ it:2000-003,
author = {Lars Ferm and Per L{\"o}tstedt},
title = {Adaptive error control for steady state solutions of
inviscid flow},
institution = it,
department = tdb,
year = 2000,
number = {2000-003},
month = feb,
abstract = {The steady state solution of the Euler equations of
inviscid flow is computed by an adaptive method. The grid
is structured and is refined and coarsened in predefined
blocks. The equations are discretized by a finite volume
method. Error equations, satisfied by the solution errors,
are derived with the discretization error as the driving
right hand side. An algorithm based on the error equations
is developed for errors propagated along streamlines.
Numerical examples from two-dimensional compressible and
incompressible flow illustrate the method. }
}
@TechReport{ it:2000-002,
author = {Biniam Gebremichael and Kidane Yemane},
title = {Linux Networking},
institution = it,
department = docs,
year = 2000,
number = {2000-002},
month = jan,
note = {M.Sc. thesis},
abstract = {Educational institutions and other groups with limited
resources can enjoy the full feature of the Unix operating
system by using the free operating system Linux. In this
thesis we present a brief discussion on the most popular
operating systems in use with a special emphasis on Linux.
We provide information and guidelines starting from Linux
installation all the way to setting up a Local Area Network
(LAN). Included is a discussion and configuration of a
dial-up network, a wireless network and LAN security.}
}
@TechReport{ it:2000-001,
author = {Richard Carlsson},
title = {Extending {E}rlang with structured module packages},
institution = it,
department = csd,
year = 2000,
number = {2000-001},
month = jan,
abstract = {This article describes a way to extend
\textsc{\mbox{Erlang}} with structured program module
packages, in a simple, straightforward and useful way.}
}
@TechReport{ it:1999-016,
author = {Arne Andersson and Mattias Tenhunen and Fredrik Ygge},
title = {Integer Programming for Automated Auctions},
institution = it,
department = csd,
year = 1999,
number = {1999-016},
month = nov,
note = {Final version published at ICMAS-00 available from
\url{http://www.csd.uu.se/~arnea/abs/icmas00.html}},
abstract = {Auctions allowing bids for combinations of items are
important for (agent mediated) electronic commerce;
compared to other auction mechanisms, they often increase
the efficiency of the auction, while keeping risks for
bidders low. The determination of an optimal winner
combination in this type of auctions is a complex
computational problem, which has recently attracted some
research, and in this paper, we look further into the topic.
It is well known that the winner determination problem for
a certain class of auctions is equivalent to what in the
operations research community is referred to as (weighted)
set packing. In this paper we compare some of the recent
winner determination algorithms to traditional set packing
algorithms, and study how more general auctions can be
modeled by use of standard integer programming methods. }
}
@TechReport{ it:1999-015,
author = {Bertil Gustafsson and Jonas Nilsson},
title = {Boundary Conditions and Estimates for the Steady Stokes
Equations on Staggered Grids},
institution = it,
department = tdb,
year = 1999,
number = {1999-015},
month = nov,
abstract = {We consider the steady state Stokes equations, describing
low speed flow and derive estimates of the solution for
various types of boundary conditions. We formulate the
boundary conditions in a new way, such that the boundary
value problem becomes non-singular. By using a difference
approximation on a staggered grid we are able to derive a
non-singular approximation in a direct way. Furthermore, we
derive the same type of estimates as for the continuous
case. Numerical experiments confirm the theoretical
results. }
}
@TechReport{ it:1999-014,
author = {Bertil Gustafsson},
title = {The {G}odunov-{R}yabenkii condition: The beginning of a
new stability theory},
institution = it,
department = tdb,
year = 1999,
number = {1999-014},
abstract = {The analysis of difference methods for initial-boundary
value problems was difficult during the first years of the
development of computational methods for PDE. The Fourier
analysis was available, but of course not sufficient for
nonperiodic boundary conditions. The only other available
practical tool was an eigenvalue analysis of the evolution
difference operator Q. Actually, there were definitions
presented, that defined an approximation as stable if the
eigenvalues of Q were inside the unit circle for a fixed
step-size h.
In the paper ``Special criteria for stability for
boundary-value problems for non-self-adjoint difference
equations'' by S.K. Godunov and V.S. Ryabenkii in 1963, the
authors presented an analysis of a simple difference scheme
that clearly demonstrated the shortcomings of the
eigenvalue analysis. They also gave a new definition of the
spectrum of a family of operators, and stated a new
necessary stability criterion. This criterion later became
known as the Godunov-Ryabenkii condition, and it was the
first step towards a better understanding of
initialboundary value problems. The theory was later
developed in a more general manner by Kreiss and others,
leading to necessary and sufficient conditions for
stability.
In this paper we shall present the contribution by Godunov
and Ryabenkii, and show the connection to the general
Kreiss theory.},
month = nov
}
@TechReport{ it:1999-013,
author = {Huimin Lin and Wang Yi},
title = {A Proof System for Timed Automata},
institution = it,
department = docs,
year = 1999,
number = {1999-013},
month = nov,
note = "To be included in the proceedings of FOSSACS'00",
abstract = {A proof system for timed automata is presented, based on a
CCS-style language for describing timed automata. It
consists of the standard monoid laws for bisimulation and a
set of inference rules. The judgements of the proof system
are \emph{conditional equations} of the form $\phi\rhd t=u$
where $\phi$ is a clock constraint and $t$, $u$ are terms
denoting timed automata. It is proved that the proof system
is complete over the recursion-free subset of the language.
The completeness proof relies on the notion of
\emph{symbolic timed bisimulation}. Two variations of the
axiomatisation are also discussed, one on timed automata by
associating an invariant constraint to each node and the
other on bisimulation by abstracting away delay transitions.}
}
@TechReport{ it:1999-012,
author = {Erik G. Larsson and Petre Stoica},
title = {Array Signal Processing with Incomplete Data},
institution = it,
department = syscon,
year = 1999,
number = {1999-012},
month = nov,
abstract = {This paper considers the problem of estimating the
Direction-of-Arrival (DOA) of one or more signals using an
array of sensors, where some of the sensors fail to work
before the measurement is completed. Methods for estimating
the array output covariance matrix are discussed. In
particular, the Maximum-Likelihood estimate of this
covariance matrix and its asymptotic accuracy are derived
and discussed. Different covariance matrix estimates are
used for DOA estimation together with the MUSIC algorithm
and with a covariance matching technique. In contrast to
MUSIC, the covariance matching technique can utilize
information on the estimation accuracy of the array
covariance matrix, and it is demonstrated that this yields
a significant performance gain. }
}
@TechReport{ it:1999-008,
author = {Bj{\"o}rn Victor and Wang Yi (Eds.)},
title = {Proceedings of the 11th Nordic Workshop on Programming
Theory},
institution = it,
department = docs,
year = 1999,
number = {1999-008},
month = oct,
url = {http://www.it.uu.se/research/publications/reports/1999-008/nwpt99/proceedings/}
}
@TechReport{ it:1999-007,
author = {Andreas Jakobsson and Marple, Jr., S. Lawrence and Petre
Stoica},
title = {Two-Dimensional Capon Spectrum Analysis},
institution = it,
department = syscon,
year = 1999,
number = {1999-007},
month = sep,
abstract = {We present a computationally efficient algorithm for
computing the 2-D Capon spectral estimator. The
implementation is based on the fact that the 2-D data
covariance matrix will have a \emph{Toeplitz-Block-Toeplitz
structure}, with the result that the inverse covariance
matrix can be expressed in closed form by using a special
case of the Gohberg-Heinig formula that is a function of
strictly the forward 2-D prediction matrix polynomials.
Furthermore, we present a novel method, based on a 2-D
lattice algorithm, to compute the needed forward prediction
matrix polynomials and discuss the difference in the
so-obtained 2-D spectral estimate as compared to the one
obtained by using the prediction matrix polynomials given
by the Whittle-Wiggins-Robinson algorithm. Numerical
simulations illustrate the clear computational gain in
comparison to both the well-known classical implementation
and the method recently published by Liu et al.}
}
@TechReport{ it:1999-006,
author = {Andreas Gustavsson and Mattias Ersson},
title = {Formalizing the Intent of Design Patterns. An Approach
Towards a Solution to the Indexing Problem},
institution = it,
department = docs,
year = 1999,
number = {1999-006},
month = jul,
abstract = {The \emph{intent} section of a pattern description is
written in easily understood, natural language, which
unfortunately has the drawback of being too imprecise and
unstructured for certain applications of the \emph{intent}
section.
We will in this essay try to formalize the intent section
of a pattern description. Our aim will be to find a
structure within the \emph{intent} description that will
reduce ambiguities and at the same time make the
classification of patterns easier. The classifications of
patterns addresses the problem of ``labeling'' patterns
into one of the following categories: Creational,
Structural or Behavioural. Succeeding in classifying
patterns by the \emph{intent} does require that enough
information for doing so is contained in the one to two
sentences that make up the \emph{intent}. Whether this is
the case or not will be discussed in the essay.
A formalized \emph{intent} section of a pattern description
can not replace the understandability of the natural
language description but can be thought of as a complement
to the standard structure to patterns today.}
}
@TechReport{ it:1999-005,
author = {Anders Jansson and Erik Lindberg and Eva Olsson},
title = {Trafiks{\"a}kerhet och informationsmilj{\"o} i
t{\aa}gf{\"o}rarsystemet. Litteratur{\"o}versikt och
olycksfallsanalyser},
institution = it,
department = hci,
year = 1999,
number = {1999-005},
month = jun,
note = {In Swedish},
abstract = {This literature survey focuses on studies of the train
driver system and its connections to other parts of the
larger train traffic system. The main part of the studies
concern Swedish conditions, but other references are
included as well.
In the first part, different ways of analysing accidents
are discussed, including organisational aspects. In the
second part, research results from different areas, all
assumed to be relevant to the train driver task, are
aggregated into a body of knowledge about the train driver
system. Comparisons are made between the train driver task
and other operator tasks. Further, the effects of a higher
degree of automation are discussed.
The task of driving a train is modelled as a dynamic
decision task, where the driver's mental representation of
the technical system and the optic flow of information are
assumed to be important parts of the train driver task.
In the last part of the literature survey, the content of
40 accident reports is discussed. Further, an analysis and
a classification of Swedish train accidents are made by
using CREAM (Hollnagel, 1998). The content of the reports,
as well as the CREAM-method are evaluated, and different
classification criteria are discussed.}
}
@TechReport{ it:1999-004,
author = {Amnon H. Eden and Yoram Hirshfeld and Amiram Yehudai},
title = {Towards a Mathematical Foundation for Design Patterns},
institution = it # {, and Tel Aviv University},
department = docs,
year = 1999,
number = {1999-004},
month = may,
abstract = {We identify a compact and sufficient set of building
blocks which constitute most design patterns of the GoF
catalog: uniform sets of classes or functions, function
clans, class hierarchies, and regularities (morphisms)
thereof. The abstractions observed are manifested within a
model in symbolic logic and defined in LePUS, a
declarative, higher order language. LePUS formulae
concisely prescribe design patterns in a general, complete,
and accurate manner. We provide a natural, condensed
graphic notation for every LePUS formula and demonstrate
how design patterns are faithfully portrayed by diagrams in
this notation. We conclude by defining refinement
(specialization) between patterns by means of predicate
calculus and illustrate how the logical formalism of LePUS
facilitates tool support for the recognition and
implementation of design patterns.}
}
@TechReport{ it:1999-003,
author = {Torsten S{\"o}derstr{\"o}m and Susanne Halvarsson},
title = {Parameter Estimation for Diffusion Models},
institution = it,
department = syscon,
year = 1999,
number = {1999-003},
month = may,
abstract = {In many applications, for example in heat diffusion and in
flow problems, it is important to describe the process
behavior inside the particular medium. An example can be
the strive for estimating certain parameters related to the
material. This paper describes how the diffusion, modeled
by a partial differential equation, can be solved using
numerical methods and how results from the field of system
identification can be utilized in order to estimate the
parameters of interest.}
}
@TechReport{ it:1999-002,
author = {Kristina Lundqvist and Lars Asplund},
title = {A Formal Model of a Ravenscar-Compliant Run-Time Kernel
and Application Code},
institution = it,
department = docs,
year = 1999,
number = {1999-002},
month = may,
abstract = {The Ravenscar tasking profile for Ada95 has been designed
to allow implementation of safety critical systems in Ada.
Ravenscar defines a tasking run-time system with
deterministic behaviour and low complexity. We provide a
formal model of the primitives provided by Ravenscar. This
formal model can be used to verify safety properties of
applications targeting a Ravenscar-compliant run-time
system. As an illustration of this, we model a sample
application and formally verify its correctness using the
real-time model checker UPPAAL.}
}
@TechReport{ it:1999-001,
author = {Torsten S{\"o}derstr{\"o}m},
title = {Perturbation Results for Singular Values},
institution = it,
department = syscon,
year = 1999,
number = {1999-001},
month = apr,
abstract = {The singular values of a perturbed complex-valued matrix
$A+\epsilon B + O(\epsilon^2)$ are shown to have singular
values of the form $\sigma_i(\epsilon)=\sigma_i +
k_i\epsilon + O(\epsilon^2)$. Explicit expressions for the
$k_i$ coefficients are derived. The cases of zero singular
values as well as multiple singular values are included in
the analysis.}
}