> On Apr 7, 2017, at 11:23 AM, Barletta, Ivano <[email protected]> wrote:
>
> 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?
The benefits of using SBAIJ matrices are
1 You don't need to compute or set values below the diagonal
2) the matrix storage requires about 1/2 the memory since the lower diagonal
part is not stored
If you use AIJ or BAIJ matrices and MatSetOption() to indicate they are
symmetric there is, of course no benefit of 1 or 2.
Barry
>
> Thanks,
> Ivano
>
> 2017-04-07 17:19 GMT+02:00 Barry Smith <[email protected]>:
>
> > On Apr 7, 2017, at 6:40 AM, Florian Lindner <[email protected]> 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;
> > }
>
>
