[petsc-dev] asm / gasm

[Mark Adams]

Thanks, I saw that.  ASM converges slower than SOR :(

On Sun, Jul 3, 2016 at 6:50 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:

>
>   Here is the problem:
>
>         if (!sz) {
>           IS       nis;
>           ierr = ISCreateGeneral(PETSC_COMM_SELF, 0, NULL,
> PETSC_COPY_VALUES, &nis);CHKERRQ(ierr);
>           ierr = PCASMSetLocalSubdomains(subpc, 1, NULL,
> &nis);CHKERRQ(ierr);
>           ierr = ISDestroy(&nis);CHKERRQ(ierr);
>
> It was setting the first IS when it should be setting the second. When I
> run after this change I get reasonable results.
>
>  0 KSP Residual norm 2.469493285658e+02
>   1 KSP Residual norm 1.335901394170e+01
>   2 KSP Residual norm 5.623002716761e-01
>   3 KSP Residual norm 5.201650164984e-02
>   4 KSP Residual norm 3.763050190737e-03
>   5 KSP Residual norm 3.024410926322e-04
> Linear solve converged due to CONVERGED_RTOL iterations 5
>   0 KSP Residual norm 2.469493285658e-03
>   1 KSP Residual norm 1.335901394170e-04
>   2 KSP Residual norm 5.623002716761e-06
>   3 KSP Residual norm 5.201650164983e-07
>   4 KSP Residual norm 3.763050190737e-08
>   5 KSP Residual norm 3.024410926322e-09
> Linear solve converged due to CONVERGED_RTOL iterations 5
>   0 KSP Residual norm 2.469493285658e-08
>   1 KSP Residual norm 1.335901394170e-09
>   2 KSP Residual norm 5.623002716761e-11
>   3 KSP Residual norm 5.201650164984e-12
>   4 KSP Residual norm 3.763050190737e-13
>   5 KSP Residual norm 3.024410926322e-14
>
>
>
> > On Jul 3, 2016, at 10:40 AM, Mark Adams <mfadams at lbl.gov> wrote:
> >
> > Barry,
> >
> > GAMG must be setting up the ASM incorrectly, on empty processors, when
> using the aggregates.  In asm.c, I see that osm->is_local is NULL for empty
> processors, and this causes a problem when this branch is taken by less
> than 8 processes (of 8):
> >
> >       if (osm->is_local) { // asm.c:282
> >        ....
> >         ierr =
> VecScatterCreate(vec,osm->is_local[i],osm->y_local[i],isl,&osm->prolongation[i]);CHKERRQ(ierr);
> >
> > I get an error "MPI_Allreduce() called in different locations (code
> lines) on different processors ", because "vec" here is global. This gamg.c
> code must not be correct:
> >
> >         if (!sz) {
> >           IS       is;
> >           ierr = ISCreateGeneral(PETSC_COMM_SELF, 0, NULL,
> PETSC_COPY_VALUES, &is);CHKERRQ(ierr);
> >           ierr = PCASMSetLocalSubdomains(subpc, 1, &is,
> NULL);CHKERRQ(ierr);
> >           ierr = ISDestroy(&is);CHKERRQ(ierr);
> >         } else {
> >           ....
> >         }
> >
> > I will look into why osm->is_local seems to be NULL here when it should
> have an empty IS.
> >
> > Mark
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-dev/attachments/20160703/75692c70/attachment.html>