I've written a write-up on PDL's wiki about using PDL and SDL to create responsive, animated simulations. You can read more about it here: . The script at the bottom of the page gives you a simulation of a bunch of noninteracting particles in a box, for which you can change the particle size, change the time step, or even reverse time. The computational code is cleanly separated from the animation code, so it should be straightforward to add particle-particle interactions if desired.
