> My cohesion algorithm is basically: if the particles touch each other, then
> they attract each other a bit, but they're repelled if they're too close.
> There's a big set of particles at the end of the animation that seem to be
> experimenting this effect, but I don't really see the effect on the rest of
> the system...

How are the particles repelled if they're too close?  Are they repelled more
strongly if they get even closer?  The reason I ask is that I think I see some
effects of increased energy in the middle of the animation (particles flying in
all directions).  This can happen if you use Euler and have strong forces.
Particles that are very close together can create immense forces to push them
apart.

An alternative (but more complicated) is to use a technique called Adaptive
Runge Kutta instead of Euler.  Adaptive Runge Kutta is much more stable and is
much less likely to give increases in energy during the animation.
Unfortunately, it will probably slow down the calculation of the physics.  If
you're stepping your particle system once for every frame with the Euler method,
Adaptive Runge Kutta will (at best) be 4 times slower.  I can provide references
if you like.

David Buck
Simberon Inc.
www.simberon.com

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