I see. So if the Mat is not known when PCSetFromOptions() is called then PCSetFromOptions() generates a bad guess for the PC to use. Presumably this has always been true. Presumably the PCSetFromOptions() has access to the DM? Can it inquire of the DM what PC to default to if the Mat is not available? Screw it, take out DM and we'll go back to the old model :-( Barry On May 6, 2012, at 12:42 PM, Jed Brown wrote:

On Sun, May 6, 2012 at 11:38 AM, Barry Smith <[email protected]> wrote: PetscErrorCode PCSetUp(PC pc) { PetscErrorCode ierr; const char *def;

PetscFunctionBegin; PetscValidHeaderSpecific(pc,PC_CLASSID,1); if (!pc->mat) SETERRQ(((PetscObject)pc)->comm,PETSC_ERR_ARG_WRONGSTATE,"Matrix must be set first");

How can it be in there without a Mat? The Mat must be set before PCSetUp().

PetscErrorCode PCSetFromOptions(PC pc) { PetscErrorCode ierr; char type[256]; const char *def; PetscBool flg;

PetscFunctionBegin; PetscValidHeaderSpecific(pc,PC_CLASSID,1);

if (!PCRegisterAllCalled) {ierr = PCRegisterAll(PETSC_NULL);CHKERRQ(ierr);} ierr = PetscObjectOptionsBegin((PetscObject)pc);CHKERRQ(ierr); if (!((PetscObject)pc)->type_name) { ierr = PCGetDefaultType_Private(pc,&def);CHKERRQ(ierr);

PetscErrorCode PCGetDefaultType_Private(PC pc,const char* type[]) { PetscErrorCode ierr; PetscMPIInt size; PetscBool flg1,flg2,set,flg3;

PetscFunctionBegin; ierr = MPI_Comm_size(((PetscObject)pc)->comm,&size);CHKERRQ(ierr); if (pc->pmat) { PetscErrorCode (*f)(Mat,MatReuse,Mat*); ierr = PetscObjectQueryFunction((PetscObject)pc->pmat,"MatGetDiagonalBlock_C",(void (**)(void))&f);CHKERRQ(ierr);