Re: negative particle sum

From: O.A. Vaquero <vaquero_at_astro.rug.nl>
Date: Thu, 04 Mar 2010 09:55:11 +0100

Robert Thompson wrote:
> I'm having an issue running a large N-Body simulation on the
> supercomputer Ranger _at_ TACC. I was able to successfully run a 2Gpc^3
> N1000^3 simulation on Lonestar (also _at_ TACC) using Gadget-3. I wanted
> to run a larger sim to examine box size effects but due to memory
> limitations on Lonestar I needed to move to Ranger. I recompiled
> gadget on Ranger, took the same parameter files from the previous 2Gpc
> run, and simply changed the box size to 3Gpc along with the particle
> count to roughly N=1500^3. The IC file was generated in the exact
> same fashion as the 2Gpc run, but again the parameter file was altered
> to change the box size and particle count. Gadget compiles and runs
> fine, except that after reading in all of the input files and
> displaying the correct total number of particles it then says that
> their sum is a negative number. The code continues to run but outputs
> very tiny snapshot files when they should be on the order of 89Gb.
>
> I have compiled the code using Ranger's pgi and intel compilers, both
> had the same result. I have also tried anywhere from 2048-4096
> processors and it all ends the same. Has anyone run into this type of
> issue before and how was it solved? I can re-run the smaller
> successful run on Ranger to see if it is system dependent but I do not
> want to waste SU's if at all possible. Thank you in advance for your
> time, there is a snippet of the log file below showing just after
> gadget finishes reading in the snapshot files. You can see that sum2
> is a negative number even though the line before it has the correct
> total particle count.
>
> -Robert Thompson
> University of Nevada Las Vegas
>
>
> reading file `/scratch/01026/tg802801/3GpcN1500_ngen/ics.127' on
> task=2032 (contains 24882176 particles.)
> distributing this file to tasks 2032-2047
> Type 0 (gas): 0 (tot= 0000000000) masstab=0
> Type 1 (halo): 24882176 (tot= 3402072064) masstab=57.7304
> Type 2 (disk): 0 (tot= 0000000000) masstab=0
> Type 3 (bulge): 0 (tot= 0000000000) masstab=0
> Type 4 (stars): 0 (tot= 0000000000) masstab=0
> Type 5 (bndry): 0 (tot= 0000000000) masstab=0
>
> reading block 0 (Coordinates)...
> reading block 1 (Velocities)...
> reading block 2 (ParticleIDs)...
> reading block 3 (Masses)...
> reading block 4 (InternalEnergy)...
> reading done.
> Total number of particles : 3402072064
>
> sum1=0 sum2=-892895232
> Testing ID uniqueness...
> success.
>
Hi Robert,

It could be that this variable (the one that turns out negative) is
defined as an integer, instead of a long integer, which would cause this
effect. When they are declared as "simple" integers, and their value
exceed the limit, they return negative values.

Hope that this is and helps.

Cheers,

Oscar
Received on 2010-03-04 09:55:15