Re: Gadget 4 Single/double precision performance

From: Tiago Castro <tiagobscastro_at_gmail.com>
Date: Sat, 12 Dec 2020 10:59:30 +0100

Many thanks, Volker

  I have re-run the code with the PRESERVE_SHMEM_BINARY_INVARIANCE and
binary compatibility has been recovered as expected. I still have a
question on this, by running the code with
PRESERVE_SHMEM_BINARY_INVARIANCE, as far as I understood, I am not changing
the accuracy or precision of my simulations, instead, I am just enforcing
the code to communicate in a specific manner. Is that right? If so, should
I interpret the difference in the outputs of runs without
PRESERVE_SHMEM_BINARY_INVARIANCE as a numerical uncertainty of my runs?

Regards,
*Tiago Castro* Post Doc, Department of Physics / UNITS / OATS
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Em sex., 4 de dez. de 2020 às 15:33, Volker Springel <
vspringel_at_mpa-garching.mpg.de> escreveu:

>
>
> Hi Tiago,
>
> > On 3. Dec 2020, at 18:58, Tiago Castro <tiagobscastro_at_gmail.com> wrote:
> >
> > Hi Volker,
> >
> > Many thanks. In fact, this was my intention, thanks for noticing my
> mistake. Re-running the code I noticed that I made another mistake
> compiling the code with EXTRA_HIGH_EWALD_ACCURACY, PMGRID, and FMM. I
> understood that for the PM-FMM gravity solver Ewald corrections were not
> needed and was expecting the sims with and without
> EXTRA_HIGH_EWALD_ACCURACY to be the same at machine precision. This is not
> the case, have I misunderstood something? Many thanks for the help.
>
> Note that Ewald corrections may still be used even if you have PMGRID,
> provided you use TREEPM_NOTIMESPLIT and you have set
> ActivePartFracForPMinsteadOfEwald to a number larger than 0.
>
> Regardless of this, binary invariance of the code's results between runs
> with the same settings, and the same MPI rank number and number of compute
> nodes, can in general only be expected if you activate
> PRESERVE_SHMEM_BINARY_INVARIANCE
>
> Regards,
> Volker
>
>
>
>
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Received on 2020-12-12 10:59:54

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