Mark F. Adams writes:

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

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Jed Brown writes:

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On Thu, Dec 29, 2011 at 11:15, Dave Nystrom <[email protected]> wrote:

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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.

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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.