>So, a particle will exchange its velocity (dx, dy, dz) with every other particle. That means that when you finish one cycle of exchanges, a particle will retain the velocity of the last particle it happened to interact with. The order of the interaction can make quite a difference, then. I would say, the FOR EACH doesn't give you a very fine control over the order in which the particles interact. Perhaps you should use an array to have a better control over this order of exchanges.


Hmmm.

Shouldn't

FOR EACH xxx IN myarray

be exactly equal to

FOR nnn = 1 to alen(myarray)
xxxx = myarray[nnn]

?