# RE: RE: Re: Gadget stalling without apparent reason

From: Raymond Carlberg <raymond.carlberg_at_utoronto.ca>
Date: Tue, 1 Nov 2016 01:26:04 +0000

I have set the minimum time step to a value below what the dynamic range should reasonably need. Indeed all is well for about ½ of the longest dynamical time. The time step does not shrink to zero, it just drops in one step.

From: isbug01_at_gmail.com [mailto:isbug01_at_gmail.com] On Behalf Of ISAAC SHLOSMAN
Sent: Monday, October 31, 2016 9:09 PM

Hi Raymond,
This because your extreme dynamic range and a finite number of time bins results in dt going to 0. Find a way to decrease dynamic range

Isaac

On Oct 31, 2016 7:45 PM, "Raymond Carlberg" <raymond.carlberg_at_utoronto.ca<mailto:raymond.carlberg_at_utoronto.ca>> wrote:
HI – I am running Gadget2 on a 32 node machine. Works well for more than 10,000 steps, then dt goes to zero with no complaints from the program so the run continues for some time with no progress. DONOTSTOP is not implemented. Softenings are good. TreeAllocFactor boosted, etc, but no go. The gravity calculation has extreme density ranges.
--Ray

Restarting shows a possible problem (Nf=0 below):
Step= 9 t= 1.55115 dt= 0.000128937
Nf= 0000064647 total-Nf= 0001622692 ex-frac= 21.9985 iter= 1
work-load balance: 18.532 max=4.10968 avg=0.221762 PE0=1.98117
max. nodes: 37131, filled: 0.0066013
part/sec=4554.93 | 245.788 ia/part=5650.51 (0)

Step= 10 t= 1.55115 dt= 0
Nf= 0000000000 total-Nf= 0001622692 ex-frac= -nan iter= 0
work-load balance: -nan max=0 avg=0 PE0=0
max. nodes: 37131, filled: 0.0066013
part/sec=0 | -nan ia/part=-nan (-nan)

^^^^^^^^^^^^^^^^^^^and the output at the time of the problem.

Begin Step 13838, Time: 1.55121, Systemstep: 0.000152588
domain decomposition...
NTopleaves= 4124
exchange of 0000288372 particles
domain decomposition done.
begin Peano-Hilbert order...
Peano-Hilbert done.
Start force computation...
Tree construction.
Tree construction done.
Begin tree force.
tree is done.
force computation done.

Begin Step 13839, Time: 1.55121, Systemstep: 0
Start force computation...
Begin tree force.
tree is done.
force computation done.

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