Hi,
I commented out the following lines in src/ksp/pc/impls/mg/mg.c
if (!lu && !redundant && !cholesky && !svd && !bjaclu) {
ierr = KSPSetType(mglevels[0]->smoothd,KSPGMRES);CHKERRQ(ierr);
}
Now the coarse KSP is set to the value given via -mg_coarse_ksp_type and
not to GMRES by default.
Is it safe to remove the above lines or it may create problems somewhere
else?
Thanks,
Michele
On Sun, 2015-07-19 at 10:33 -0400, Mark Adams wrote:
> 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 <[email protected]>
> wrote:
>
> On Sat, Jul 18, 2015 at 10:31 PM, Michele Rosso
> <[email protected]> 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
> > <[email protected]> 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
> <[email protected]> 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
>
>
>
