[petsc-users] pctype comparison

[Barry Smith]

On May 7, 2013, at 6:42 AM, Matthew Knepley <knepley at gmail.com> wrote:

> On Tue, May 7, 2013 at 4:49 AM, Frederik Treue <frtr at fysik.dtu.dk> wrote:
> Hi,
> 
> is there any way of checking which type of PC you are using in the code?
> Ie. I want to do something like:
> 
> http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Sys/PetscObjectTypeCompare.html
> 
>    Matt
>  
> ...
> PCType mytype;
> PC pc;
> if (PhaseOfTheMoon==waxing) {
>         mytype=PCJacobi;
> } else {
>         mytype=PCMG;
> }
> ...
> ierr=PCSetType(pc,mytype);CHKERRQ(ierr);
> if (mytype==PCMG) {
>   ierr=PCMGSetLevels(pc,levels,PETSC_NULL);CHKERRQ(ierr);
>   …
  

    Note that also PETSc is designed to ignore options for types that are not being used. So you do not need the 
if (mgtype == PCMG) { stuff at all 

   simply write

     PCSetFromOptions(pc);
     ierr=PCMGSetLevels(pc,levels,PETSC_NULL);CHKERRQ(ierr);   /* will only activate if a MG PC selected
     ierr =PCFactorSetLevels(pc,2);   /* will only activate if a factorization based preconditioner
     etc etc

   Barry


> }

> ...
> 
> But since mytype is apparently a pointer type, this doesn't work.
> 
> /Frederik Treue
> 
> 
> 
> 
> 
> -- 
> What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.
> -- Norbert Wiener