Maximum Number of Tree Nodes Reached

From: Jared Coughlin <Jared.W.Coughlin.29_at_nd.edu>
Date: Fri, 10 Nov 2017 00:00:17 -0500

Hello! I've run three dark matter only simulations with N = 1024^3
particles and L = 40 Mpc/h. Each simulation is started from the same
initial conditions (generated using 2LPTic) and being run on 72 processors
(each node of the supercomputer I'm using has 24 processors and 256GB of
RAM, so I'm using 3 full nodes). I save five snapshots. However, once the
simulations are done (they all run successfully), I need to know the
density field, so I have a quick code that simply reads the snapshot and
changes the particle types from 1 to 0. I then use gadget's density
calculation on each snapshot in order to get smoothing lengths and
densities for each of my particles. The reason I'm doing the whole
simulation as pure N-body is for run-time reasons.

For two of my simulations (the non-standard dark energy ones), this works
like a charm and gives me what I need for each of the total of ten
snapshots. However, for the cosmological constant simulation, only four out
of the five snapshots run successfully. The one snapshot at z = 3 fails
with the error "task 57: maximum number 25836911 tree-nodes reached." I've
tracked this down to the while(1) loop in force_treebuild_single() in
forcetree.c. I should also note that I've run plenty of cosmological
constant simulations using this method in the past, with the only
difference being that those ones has fewer particles (I've even run one
that had the same resolution successfully, 428^3 particles in a 15Mpc/h
box).

I've read the other questions concerning this error on the mailing list,
but their solutions do not appear to be working for me. I increased
TreeAllocFac to 1.5 without changing the number of processors, and then I
also increased the number of processors to 96 and it still fails. I've been
attempting to understand the inner workings of the tree construction for
the last several days, but I'm getting nowhere quite quickly.

What's really confusing me is why all the other snapshots worked just fine.
I cannot for the life of me figure out what is different about this one, so
if anyone has any thoughts on what causes this error, I would love to hear
them. Thank you very much for your time!

Sincerely,
-Jared
Received on 2017-11-10 06:00:20

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