[petsc-users] KSP changes for successive solver

[Mark Adams]

This was fixed on June 18 (Stephen Kramer):


> Can you please test this and see if works, without your fix?
>
>   'git fetch; git checkout mark/gamg-crs',
>

Great! That fixes everything for me: it uses KSP+PREONLY for mg_coarse by
default again and I can also override it with -mg_coarse_ksp_type

Thanks a lot for fixing this
Cheers

This was soon merged to master & next.  In src/ksp/pc/impls/mg/mg.c we have:

    ierr = PetscObjectTypeCompare((PetscObject)cpc,PCLU,&lu);CHKERRQ(ierr);
    ierr =
PetscObjectTypeCompare((PetscObject)cpc,PCREDUNDANT,&redundant);CHKERRQ(ierr);
    ierr =
PetscObjectTypeCompare((PetscObject)cpc,PCCHOLESKY,&cholesky);CHKERRQ(ierr);
    ierr =
PetscObjectTypeCompare((PetscObject)cpc,PCSVD,&svd);CHKERRQ(ierr);
    if (!lu && !redundant && !cholesky && !svd && !bjaclu) {
      ierr = KSPSetType(mglevels[0]->smoothd,KSPGMRES);CHKERRQ(ierr);
    }

Perhaps our logic is failing here?  This is the only place where
GMRES spontaneously appears.  We should really remove this altogether.



On Sat, Jul 18, 2015 at 11:40 PM, Matthew Knepley <knepley at gmail.com> wrote:

> On Sat, Jul 18, 2015 at 10:31 PM, Michele Rosso <mrosso at uci.edu> wrote:
>
>>  Matt,
>>
>> please find the log_summary attached.
>>
>
> Okay, it is running master. Barry, where should he look in the code to see
> why its still changing,
> meaning what changeset fixed this?
>
>   Thanks,
>
>     Matt
>
>
>> Michele
>>
>>
>> On Sat, 2015-07-18 at 21:56 -0500, Matthew Knepley wrote:
>>
>> On Sat, Jul 18, 2015 at 9:53 PM, Michele Rosso <mrosso at uci.edu> wrote:
>>
>>  Barry,
>>
>> I tried the master branch of PETSc as you suggested and unfortunately the
>> problem with KSP being set to GMRES on the coarse level when using
>> "-mg_coarse_ksp_type preonly"  is still there. I attached the output from
>> ksp view and the options stack.
>> Am I missing something?
>>
>>
>>
>>  If you show output from -log_summary we can make sure you are running
>> the version we expect.
>>
>>
>>
>>    Thanks,
>>
>>
>>
>>      Matt
>>
>>
>>
>>  Thanks,
>> Michele
>>
>>
>> On Thu, 2015-07-16 at 17:30 -0500, Barry Smith wrote:
>>
>>    Michel,
>>
>>     This is a very annoying feature that has been fixed in master http://www.mcs.anl.gov/petsc/developers/index.html  I would like to have changed it in maint but Jed would have a shit-fit :-) since it changes behavior.
>>
>>   Barry
>> > On Jul 16, 2015, at 4:53 PM, Michele Rosso <mrosso at uci.edu> wrote:> > Hi,> > I am performing a series of solves inside a loop. The matrix for each solve changes but not enough to justify a rebuilt of the PC at each solve.> Therefore I am using  KSPSetReusePreconditioner to avoid rebuilding unless necessary. The solver is CG + MG with a custom  PC at the coarse level.> If KSP is not updated each time, everything works as it is supposed to. > When instead I allow the default PETSc  behavior, i.e. updating PC every time the matrix changes, the coarse level KSP , initially set to PREONLY, is changed into GMRES > after the first solve. I am not sure where the problem lies (my PC or PETSc), so I would like to have your opinion on this.> I attached the ksp_view for the 2 successive solve and the options stack.> > Thanks for your help,> Michel> > > > <ksp_view.txt><petsc_options.txt>
>>
>>
>>
>>
>>
>>
>>
>>  --
>>
>>  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
>>
>>
>>
>
>
> --
> 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
>
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