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

[Dave Nystrom]

Mark F. Adams writes:
 > 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);

Shouldn't it be

ierr = MatSetBlockSize(Amat,2);      CHKERRQ(ierr);

since I have 2x2 blocks.

 > > 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.
 > > 
 > 
 >