@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 = {Department of Information Technology, Uppsala University}, department = {Division of Scientific Computing}, 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.} }