[petsc-users] Symmetric matrix: Setting entries below diagonal

[Barletta, Ivano]

So, as far as I understand, the only benefit of PETSc with symmetric
matrices
is only when Matrix values are set, by reducing the overhead of MatSetValue
calls?

Thanks,
Ivano

2017-04-07 17:19 GMT+02:00 Barry Smith <bsmith at mcs.anl.gov>:

>
> > On Apr 7, 2017, at 6:40 AM, Florian Lindner <mailinglists at xgm.de> wrote:
> >
> > Hello,
> >
> > two questions about symmetric (MATSBAIJ) matrices.
> >
> > + Entries set with MatSetValue below the main diagonal are ignored. Is
> that by design?
>
>    Yes
>
> > I rather expected setting A_ij to
> > have the same effect as setting A_ji.
>
>    You need to check the relationship between i and j and swap them if
> needed before the call.
>
> >
> > + Has MatSetOption to MAT_SYMMETRIC and MAT_SYMMETRIC_ETERNAL any gain
> on MATSBAIJ matrices?
>
>   No
>
> >
> > Thanks,
> > Florian
> >
> > Test programm:
> >
> >
> > #include "petscmat.h"
> > #include "petscviewer.h"
> >
> > int main(int argc, char **argv)
> > {
> >  PetscInitialize(&argc, &argv, "", NULL);
> >  PetscErrorCode ierr = 0;
> >
> >  Mat A;
> >  ierr = MatCreate(PETSC_COMM_WORLD, &A); CHKERRQ(ierr);
> >  MatSetType(A, MATSBAIJ); CHKERRQ(ierr);
> >  ierr = MatSetSizes(A, 4, 4, PETSC_DECIDE, PETSC_DECIDE); CHKERRQ(ierr);
> >  ierr = MatSetUp(A); CHKERRQ(ierr);
> >  ierr = MatSetOption(A, MAT_SYMMETRIC, PETSC_TRUE); CHKERRQ(ierr);
> >  ierr = MatSetOption(A, MAT_SYMMETRY_ETERNAL, PETSC_TRUE); CHKERRQ(ierr);
> >
> >  // Stored
> >  ierr = MatSetValue(A, 1, 2, 21, INSERT_VALUES); CHKERRQ(ierr);
> >  ierr = MatSetValue(A, 1, 1, 11, INSERT_VALUES); CHKERRQ(ierr);
> >
> >  // Ignored
> >  ierr = MatSetValue(A, 2, 1, 22, INSERT_VALUES); CHKERRQ(ierr);
> >  ierr = MatSetValue(A, 3, 2, 32, INSERT_VALUES); CHKERRQ(ierr);
> >  ierr = MatSetValue(A, 3, 1, 31, INSERT_VALUES); CHKERRQ(ierr);
> >
> >  ierr = MatAssemblyBegin(A, MAT_FINAL_ASSEMBLY); CHKERRQ(ierr);
> >  ierr = MatAssemblyEnd(A, MAT_FINAL_ASSEMBLY); CHKERRQ(ierr);
> >
> >  PetscViewer viewer;
> >  ierr = PetscViewerCreate(PETSC_COMM_WORLD, &viewer); CHKERRQ(ierr);
> >  ierr = PetscViewerSetType(viewer, PETSCVIEWERASCII); CHKERRQ(ierr);
> >  ierr = PetscViewerPushFormat(viewer, PETSC_VIEWER_ASCII_DENSE);
> CHKERRQ(ierr);
> >  ierr = MatView(A, viewer); CHKERRQ(ierr);
> >  ierr = PetscViewerPopFormat(viewer); CHKERRQ(ierr);
> >  ierr = PetscViewerDestroy(&viewer); CHKERRQ(ierr);
> >
> >  PetscFinalize();
> >  return 0;
> > }
>
>
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