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

[Jed Brown]

On Thu, Dec 29, 2011 at 11:51, Dave Nystrom
<Dave.Nystrom at tachyonlogic.com>wrote:

> Both although the most challenging problem right now is one for a Hall
> matrix
> system that is block banded with 2x2 blocks.
>

What is the null space of this operator.


>  Right now, I am just inputting
> the matrix into a petsc seqaij matrix.  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.
>

PCGAMG currently takes coordinates for a nodal basis, from which it
generates a null space (making assumptions about the equations). I have it
on my list to update so that you can call MatSetNearNullSpace() and have
PCGAMG use this null space.
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