[Users] Meeting minutes for 2025-01-16

[Bruno Giacomazzo]

Regarding the BNS issues, is it something due to when you recover from
checkpoint?

In Whisky we had an issue related to that due to Con2Prim running after
recovery from checkpoint.

E.g., you run a simulation from iteration 0 to iteration 24 (made up
numbers just to explain myself).
You try the same simulation, but this time you run from 0 to 12,
checkpoint, recover from checkpoint and run from 12 to 24.
The results between  these two simulations at iteration 24 were slightly
different

The issue was in the Newton Raphson being called by Con2Prim and using a
different initial guess when recovering from checkpoint. During a run it
uses the previous values of the primitive variables as an initial guess,
but these are not available when restarting from checkpoint. The solution,
as far as I remember, was not to run Con2Prim during recovery from
checkpoint (since the primitive variables are anyway recovered from the
checkpoint files).

Cheers,
Bruno


Il giorno gio 16 gen 2025 alle ore 19:59 Roland Haas <rhaas at illinois.edu>
ha scritto:

> Hello all,
>
> > # Reproducibility issues with BNS
> >   * Wolfgang Tichy has obtained different results with different MPI
> ranks on
> Sorry, my bad. Correction: Michal Pirog (who is working with Wolfgang)
> noticed these.
>
> Yours,
> Roland
>
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-- 

Prof. Bruno Giacomazzo
Deputy Director of the Department of Physics
University of Milano-Bicocca
Piazza della Scienza 3
20126 Milano
Italy

email: bruno.giacomazzo at unimib.it
phone: (+39) 02 6448 2321
web: http://www.brunogiacomazzo.org

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