Simulating Negative mass particles.

From: Cassandra Hall <>
Date: Thu, 3 Sep 2015 12:08:43 +0000

Hi All.

I am having a problem when trying to simulate negative mass particles (the fact that I have a problem isn't unsurprising) and was wondering if anyone could shed some light.

When I try to simulate positive and negative mass particles with periodic boundaries, in forcetreeevaluate_shortrange the tabindex goes negative, resulting in a seg fault.

This trivially appears to be due to the boxsize being too small, however I don't quite understand what's happening.

If I make the periodic box larger, I end up with a timestep of size zero error (possibly a seperate problem that is fixed by multiplying by the right sign during timestep evaluation).

The variables are below - since tabindex = (long long)((asmthfac * r)+0.5);

i: 2059, r2: 133688530459941255774208.000000, 229950405312.035156 109523914353.468750 262327760142.662109
pos_x 15183.964844 pos_y 92062.531250 pos_z 16641.337891
mass 0.000122
nop 38989024
no 27353
All.MaxPart 26214
i:2059 tabindex:-1348600960
0.113778 365634421875.103638
Segmentation fault

Does anybody have any suggestions as to why this may be happening? I have no doubt it's me being an idiot.....

Thanks a lot

Received on 2015-09-03 14:55:59

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