18 February 2007

Barnes-Hut Tree Code Submitted to PlaneT

I've just submitted some new code to PlaneT which implements Barnes-Hut Trees in PLT Scheme. It's surprisingly (to me) fast, creating a 100K-body tree in about 30 seconds on my old PowerBook G4 800 Mhz.

This is just another step in my code clean-up in preparation for comparing our algorithm to the standard leapfrog algorithm of cosmological codes.

N-Body Simulation Initial Conditions

I just packaged up some code for PlaneT which creates gravitational N-body initial conditions. I assume it'll appear in the next few days. It's not very extensive as of yet (only does cold and hot constant spatial density spherical distributions and the venerable Plummer model), but that's really all I've needed over the past year or so to test my algorithms.

The paper is undergoing its final revisions, and the referee has indicated that these will make it acceptable, so I think we're in the home stretch of getting it published. That means that I'm consolidating my code a bit in preparation for testing our algorithm on Barnes-Hut-style cosmological simulations. The PlaneT package is a result of that consolidation.

My current plan is to gin up a prototype Barnes-Hut tree code in PLT Scheme (shouldn't take long---it's really pretty easy to code). Once I've got that working, I'll start converting the important bits to C that I can link into PLT Scheme. This is for speed. The IC code currently takes about 2 minutes on my machine to generate a million-body system, while similar C code I've used takes as short as 10 seconds. There will likely be a similar factor for the integrator code.

We'll be wanting to test our integrator on large systems (i.e. around a million bodies), so coding the bottlenecks in C will be necessary. I'll be using as little of it as possible, however, because scheme is so much more pleasant.

I'm looking at this future work as a grand experiment to see whether it's practical to develop physics simulation code this way. I know that other people have done it before, but I want to see how it works for me.