where [f.sub.[alpha]] is the distribution function of particles moving with velocity [e.sub.[alpha]], [[LAMBDA].sub.[alpha]j] is the collision matrix, [f.sup.eq] is the equilibrium distribution function, and [F.sub.[alpha]] is the external force.
For the single-relaxation-time (SRT) model, the collision matrix is [[LAMBDA].sub.[alpha]j] = -1/[tau][[delta].sub.[alpha]j], where [[delta].sub.[alpha]j] is the Kronecker symbol and t is the relaxation time which is related to the kinetic viscosity by v = [c.sup.2.sub.s]([tau] - 1/2)[delta]t.