[petsc-dev] Seeking Advice on Petsc Preconditioners to Try

[Mark F. Adams]

On Dec 29, 2011, at 12:51 PM, Dave Nystrom wrote:

> Jed Brown writes:
>> On Thu, Dec 29, 2011 at 11:15, Dave Nystrom <dnystrom1 at comcast.net> wrote:
>> 
>>> I have tried out -ksp_type cg -pc_type gamg -pc_gamg_type sa on my problem
>>> and am encouraged enough with the results that I would like to try taking
>>> the
>>> next step with using gamg.  Could you provide some advice on how to do
>>> that?
>>> I'm not sure how to provide the null space info you say is important.
>>> 
>> 
>> Are you solving a scalar or vector problem?
> 
> Both although the most challenging problem right now is one for a Hall matrix
> system that is block banded with 2x2 blocks.  Right now, I am just inputting
> the matrix into a petsc seqaij matrix.  

Thats fine, actually require.  Just call this:

ierr = MatSetBlockSize(Amat,3);      CHKERRQ(ierr);

> I guess I need to put it into a petsc
> block matrix but have not yet attempted to do that.  I'm not sure how much
> work is involved - I need to read the section in the users manual on that.
> 
> Anyway, I have 5 scalar systems and on vector system with 2x2 blocks.  I am
> interested in applying gamg to all of them to see how well it works.
>