[petsc-users] GMRES Breakdown

[Matthew Knepley]

On Tue, Sep 28, 2021 at 8:39 AM TARDIEU Nicolas via petsc-users <
petsc-users at mcs.anl.gov> wrote:

> Dear PETSc Team,
>
> We, code_aster's development team, are using PETSc in our application for
> years now, mainly for the KSP et PC features. We run tests cases every week
> without problems.
> After upgrading from PETSc 3.12.3 to 3.15.3, a test case using GMRES
> failed with KSP_DIVERGED_BREAKDOWN. By rolling back to 3.12.3, we have
> checked that the upgrade is the origin of the failure.
>
> We know this can occur with GMRES but it is the first time we are facing
> this situation.
>
> Is it a bug ? If yes, how can we help to fix it ? If no, what can we do ?
> Could the flexible version of GMRES be an alternative ?
>
This is not a bug, but we did change the operation. We now check whether
there is a significant residual spike after a restart. We
want to let the user know that this likely means that the solver is
inappropriate for the problem. As Jose notes, you can turn off this
behavior.

  Thanks,

     Matt


> Best regards,
> Nicolas
> --
> *Nicolas Tardieu*
> *Ing, PhD*
>
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-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener

https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
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