PetscErrorCode MyDMComputeFunction(DM dm,Vec x,Vec F)
{
PetscErrorCode ierr;
Mat J;
PetscFunctionBegin;
ierr = DMGetApplicationContext(dm,&J);CHKERRQ(ierr);
if (!J) {
ierr = DMCreateMatrix(dm,MATAIJ,&J);CHKERRQ(ierr);
ierr = PetscObjectCompose((PetscObject)J,"DM",(PetscObject)PETSC_NULL);CHKERRQ(ierr);
ierr = FormMatrix(dm,J);CHKERRQ(ierr);
ierr = DMSetApplicationContext(dm,J);CHKERRQ(ierr);
ierr = DMSetApplicationContextDestroy(dm,(PetscErrorCode (*)(void**))MatDestroy);CHKERRQ(ierr);
}
ierr = MatMult(J,x,F);CHKERRQ(ierr);
PetscFunctionReturn(0);
}
PetscErrorCode MyComputeFunction(SNES snes,Vec x,Vec F,void *ctx)
{
PetscErrorCode ierr;
Mat J;
DM dm;
PetscFunctionBeginUser;
ierr = SNESGetDM(snes,&dm);CHKERRQ(ierr);
ierr = DMGetApplicationContext(dm,&J);CHKERRQ(ierr);
if (!J) {
ierr = DMCreateMatrix(dm,MATAIJ,&J);CHKERRQ(ierr);
ierr = MatSetDM(J, PETSC_NULL);CHKERRQ(ierr);
ierr = FormMatrix(dm,J);CHKERRQ(ierr);
ierr = DMSetApplicationContext(dm,J);CHKERRQ(ierr);
ierr = DMSetApplicationContextDestroy(dm,(PetscErrorCode (*)(void**))MatDestroy);CHKERRQ(ierr);
}
ierr = MatMult(J,x,F);CHKERRQ(ierr);
PetscFunctionReturn(0);
}
