Am Freitag, 6. Mai 2005 16:58 schrieb Greg Buchholz:
Daniel Fischer wrote:
The problem is that a prime crept in in Josef's code, so to calculate the positions and velocities, the updated versions of the planets are used, it should be
Ah, yes, thanks for the correction.
Besides, offset_momentum does not use the parameter n at all and I think that all the indexing in the computation of the potential energy is rather inefficient.
I wasn't too worried about the energy function, since it only gets called twice, whereas the "advance" get called potentially millions of
Of course, and for only five bodies...
times (and must be the source of the space leak). You can see one profile I ran (for n=1000 instead of 1000000) at...
I did profiling for n = 20000 and n = 100000, if I read the profiles correctly, Josef's code reduces memory usage by a factor of 2 resp. 3, which ain't bad. Maybe one could reduce space usage further by not creating the list of iterations but instead make it a tail recursive function? I'll try.
http://sleepingsquirrel.org/nbody/nbody.prof
Thanks,
Greg Buchholz
One question: the energy of the system should be constant - that little physics I know. What I don't know is whether the change in energy in this simulation is within usual, reasonable bounds or not. If not, is it due to a too long time interval or should one use a more sophisticated algorithm? Cheers, Daniel