Re: PM particle out of bounds error.

From: Volker Springel <volker_at_MPA-Garching.MPG.DE>
Date: Mon, 08 May 2006 17:07:31 +0200

Brad Krane wrote:
> Hello,
> I've been running the sample galaxy and after a while i get the following error:
>
> Begin Step 945, Time: 1.46332, Systemstep: 0.00152588
> Start force computation...
> Begin tree force.
> tree is done.
> force computation done.
>
> Begin Step 946, Time: 1.46484, Systemstep: 0.00152588
> domain decomposition...
> NTopleaves= 162
> work-load balance=1 memory-balance=1
> domain decomposition done.
> begin Peano-Hilbert order...
> Peano-Hilbert done.
> Start force computation...
> Starting non-periodic PM calculation (grid=0).
> Particle Id=22724 on task=0 with coordinates (-2.06614|201.518|-4.22598) lies ou
> tside PM mesh.
> Stopping
> In total 4 particles were outside allowed range.
>
> Allowed region for isolated PM mesh (coarse):
> (-191.952|-181.732|-189.058) -> (191.743|201.963|194.637) ext=383.695 totmes
> hsize=798.983 meshsize=3.12103
>
> Starting non-periodic PM calculation (grid=0).
> Particle Id=37074 on task=0 with coordinates (-191.952|22.8454|7.37917) lies out
> side PM mesh.
> Stopping
> In total 1 particles were outside allowed range.
> task 0: endrun called with an error level of 68687
>
> What would cause this and how would I fix it? I suspect that I may
> need to change a value in the galaxy.param file but looking over the
> documentation I still don't know what might fix this.
>

You need to set the compile-time parameter ENLARGEREGION to a value
larger than 1.0 (say 1.1 or 1.2) to solve this problem.

You are here using the PM method for a simulation of an isolated problem
with a changing spatial extension - this is possible, but typically not
a good idea. When a particle leaves the region covered by the PM mesh,
the code tries to place a new mesh by determining the maximum extension
of the particle distribution. When ENLARGEREGION is not declared
otherwise, a value of 1.0 is assumed, meaning that one particle will be
exactly on the boundary of the newly determined region. Depending on
floating point rounding, the code may then think that the particle is
already outside again, producing the above sequence of errors. However,
if ENLARGEREGION=1.1 is used, for example, the particle distribution may
extend by 10% before a new mesh needs to be found.

Note that examples for suitable makefiles for the galaxy problem are
also included in the code distribution, in the parameterfiles/
subdirectory, and this did not recommend the PM algorithm for this problem.

Volker



> Thank you.
>
>
> --
> Brad
>
>
>
>
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Received on 2006-05-08 17:07:31

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