[petsc-users] Setting/creating Mats for SNES use

[Justin Chang]

Hi all,

In my DMPlex program, I have these lines:

Mat A,J;

...

ierr = DMSetMatType(dm, MATAIJ); CHKERRQ(ierr);
ierr = DMCreateMatrix(dm, &J); CHKERRQ(ierr);
A = J;

ierr = DMSNESSetFunctionLocal(dm, ...); CHKERRQ(ierr);
ierr = DMSNESSetJacobianLocal(dm, ...); CHKERRQ(ierr);
ierr = SNESSetJacobian(snes, A, J, NULL, NULL); CHKERRQ(ierr);
ierr = SNESSetFromOptions(snes); CHKERRQ(ierr);

...

ierr = SNESSolve(snes, NULL, x); CHKERRQ(ierr);

...
ierr = MatDestroy(&J); CHKERRQ(ierr);


For the line "A = J;", what exactly is the difference, if any, between that
and "ierr = MatDuplicate(...)" or "ierr = MatCopy(...)"? Do these different
options somehow affect memory usage/performance? Say I am solving a
standard poisson equation using either GAMG and/or HYPRE.

Thanks,
Justin
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