Re: [petsc-dev] asm / gasm

3 Jul 2016


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

On Sun, Jul 3, 2016 at 6:50 PM, Barry Smith <[email protected]> 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 <[email protected]> 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

Mark Adams

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