Conservative method for the reduction of the number of particles in the Monte Carlo simulation method for kinetic equations

A method for the reduction of the number of particles in the weighted Monte Carlo method for kinetic equations is described. The method randomly redistributes statistical weights over the particle ensemble in such a way that the weight of some particles becomes 0, i.e., the particles are cancelled, while all physically relevant macroscopic moments (e.g., mass, energy, momentum) of the ensemble do not change. The method has been applied to the spatially uniform relaxation of a gas of hard spheres.