[petsc-users] Use of KSPSetOperators

[Barry Smith]

> On Mar 17, 2015, at 4:26 PM, Chung-Kan Huang <ckhuangf at gmail.com> wrote:
> 
> Hi,
> 
> I am a little confused about the statement in KSPSateOperators.
> 
> 
>         KSP/PCGetOperators
> (ksp/pc,&mat,&pmat); is equivalent to
> 
>           set size, type, etc of mat and pmat
> 
> 
>         MatCreate
> (comm,&mat);
> 
>         MatCreate
> (comm,&pmat);
> 
>         KSP/PCSetOperators
> (ksp/pc,mat,pmat);
> 
>         PetscObjectDereference((PetscObject
> )mat);
> 
>         PetscObjectDereference((PetscObject
> )pmat);
> 
>           set size, type, etc of mat and pmat
> 
> 
> 
> In my case I want to construct preconditioner from P which will be assembled differently from A.
> 
> So I only need to do 
> KSPSetOperators(ksp, A, P);
> after A & P are created.
> 
> or do I need to also do 
> PCSetOperators(pc, A, P);
> as well?
> 
> and what are those PetscObjectDereference about?
> 
> I have tried doing only 
> KSPSetOperators(ksp, A, P);
> 
> and I saw the performance of linear solver changed and I got right answer but I am not sure is if it was doing the thing I think it was doing.

   This is what you should be doing so it is fine. You can ignore all that other stuff.

 Barry

> 
> And is it anyway to know if it is doing what I am asking?
> 
> Thanks,
> 
> Kan
> -- 
> Cheers
>