Brownian motion is the random motion of particles. This movement causes the diffusion. It is observed as the result of their collision with the fluid. All particles are assumed to move independently because their density is far smaller than that of fluid. You can set parameters of the number of particles and movement velocity. In this simulator, the positions are calculated recurrently by this function.
Positiont+1(x,y)=v*Random(x,y)+Positiont(x,y)
Random(x,y) is the random vector of -1<x<1 and -1<y<1. The value v is the parameter of movement velocity.