  The Stochastic Weighted Particle Method (SWPM) is a Monte Carlo technique
developed by Rjasanow and Wagner that generalizes Bird's Direct Simulation
Monte Carlo (DSMC) method for solving the Boltzmann equation. To reduce
computational cost due to the gradual increase in the number of stochastic
particles in the SWPM, Rjasanow and Wagner proposed several particle reduction
schemes designed to preserve specified moments of the velocity distribution.
Here, we introduce an improved particle reduction scheme that preserves all
moments of the velocity distribution up to the second order, as well as the raw
and central heat flux both within each group of particles to be reduced and for
the entire system. Furthermore, we demonstrate that with the new reduction
scheme the scalar fourth-order moment can be computed more accurately at a
reduced computational cost.
