[petsc-users] KSP changes for successive solver
Michele Rosso
mrosso at uci.edu
Sun Jul 19 11:08:50 CDT 2015
Mark,
at first I thought the problem was due to my custom PC, but the same
happens if I use (see attached files):
-mg_coarse_ksp_type preonly
-mg_coarse_pc_type gamg
If instead I use a direct solver, say:
-mg_coarse_ksp_type preonly
-mg_coarse_pc_type lu
the coarse KSP is set correctly.
Michele
On Sun, 2015-07-19 at 10:42 -0400, Mark Adams wrote:
>
>
>
>
> On Thu, Jul 16, 2015 at 5:53 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.
>
>
>
> Ah, OK this is the problem. The code I just sent gets fooled but your
> custom PC, probably.
>
>
> We should just remove this paternal code:
>
>
> PetscBool preonly,lu,redundant,cholesky,svd
>
>
>
> ...
>
>
>
>
> /*
> If coarse solver is not direct method then DO NOT USE preonly
> */
> ierr =
> PetscObjectTypeCompare((PetscObject)mglevels[0]->smoothd,KSPPREONLY,&preonly);CHKERRQ(ierr);
> if (preonly) {
> ierr =
> PetscObjectTypeCompare((PetscObject)cpc,PCBJACOBI,&bjaclu);CHKERRQ(ierr);
> if (bjaclu) {
> KSP *k2;
> PetscInt ii,first;
> ierr = PCBJacobiGetSubKSP(cpc,&ii,&first,&k2);CHKERRQ(ierr);
> if (ii==1) {
> PC pc2;
> ierr = KSPGetPC(k2[0],&pc2);CHKERRQ(ierr);
> ierr =
> PetscObjectTypeCompare((PetscObject)pc2,PCLU,&bjaclu);CHKERRQ(ierr);
> }
> else bjaclu = PETSC_FALSE;
> }
> 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);
> }
> }
>
>
>
>
>
> 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
>
>
>
>
>
>
>
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