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

[Florian Lindner]

Hello,

two questions about symmetric (MATSBAIJ) matrices.

+ Entries set with MatSetValue below the main diagonal are ignored. Is that by design? I rather expected setting A_ij to
have the same effect as setting A_ji.

+ Has MatSetOption to MAT_SYMMETRIC and MAT_SYMMETRIC_ETERNAL any gain on MATSBAIJ matrices?

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;
}