Re: Run-time error: A timestep of size zero was assigned

From: Volker Springel <volker_at_MPA-Garching.MPG.DE>
Date: Sat, 10 Jun 2006 15:45:52 +0200

I agree with all of Yves comments. There is one further thing worth
checking: Make sure that all of the particle types that are used in the
simulation have a non-zero gravitational softening. The code cannot work
if you use zero softening, and will produce NaN in this case.

Volker


Yves Revaz wrote:
>
> Hugo,
>
> According to my experience with Gadget, I would proceed this way :
>
> 1) If you have modified some parts of the code, check that these parts
> may not be at the origin of a NaN of Inf problem.
>
> 2) Check that the snapshot from which you re-start the simulation do not
> contains Nan or Inf numbers, or isolated particles at very large
> distance from the
> center of mass or very large velocities.
>
> 3) The fact that the problem is related to the node 14 probably is
> linked to the
> fact that the problematic particles are treated by this node. However,
> to test the hardware
> of node 14, simply try to remove it from the list of the used nodes and
> see if the
> problem still occur.
>
> I hope it will help.
>
> Regards.
>
>
>
>
>
>
> Hugo Vicente Capelato wrote:
>
>> Dear Ives
>>
>> Thank you for your answer. The problem is that this error
>> is coming intermittently and, seemingly, more and more frequently.
>>
>> Restarting Gadget from the point it stopped makes it goes somewhat
>> further in time, but after while it stops again with the same error,
>> but not for the same particle as, for instance, like this:
>>
>> =====================
>> Begin Step 52398, Time: 0.190878, Systemstep: 4.76837e-06
>> domain decomposition...
>> NTopleaves= 2360
>> work-load balance=1.3816 memory-balance=1.754
>> exchange of 0000017839 particles
>> domain decomposition done.
>> begin Peano-Hilbert order...
>> Peano-Hilbert done.
>> Start force computation...
>>
>> Error: A timestep of size zero was assigned on the integer timeline!
>> We better stop.
>> Task=14 Part-ID=372839 dt=nan tibase=3.72529e-08 ti_step=-2147483648 ac=nan
>> xyz=(-194.79|219.205|427.333) tree=(nan|nannan)
>>
>> Tree construction.
>> Tree construction done.
>> Begin tree force.
>> tree is done.
>> =======================
>>
>> However it is seems to be always the same "Task=14" which, I suppose,
>> corresponds to certain node of the cluster. I am suspecting of a
>> hardware problem... What do you think ?
>>
>> Cheers, Hugo
>>
>> Quoting Yves Revaz <yves.revaz_at_obs.unige.ch>:
>>
>>
>>
>>> Dear Hugo,
>>>
>>> This means that the timestep for particle 346505 computed by get_timestep()
>>> is equal to zero or is not a number (nan), which should not occure.
>>> In this case the program is of course stopped.
>>>
>>> In you case, the log also says "ac=nan" which is not very nice...
>>> This is probably due to zero division or overflow during force computation.
>>>
>>> Regards.
>>>
>>>
>>>
>>>
>>>
>>>> Error: A timestep of size zero was assigned on the integer timeline!
>>>> We better stop.
>>>> Task=14 Part-ID=346505 dt=nan tibase=3.72529e-08 ti_step=-2147483648
>>>> ac=nan xyz=
>>>> (-199.269|226.042|432.335) tree=(nan|nannan)
>>>>
>>>>
>>>>
>>>>
>>>>
>>> --
>>> (o o)
>>> --------------------------------------------oOO--(_)--OOo-------
>>> Yves Revaz
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>>> FRANCE
>>> ----------------------------------------------------------------
>>>
>>>
>>>
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>>
>>
>>
>
>
>
>
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Received on 2006-06-10 15:46:16

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