[petsc-users] about pclu

[Ryan Yan]

Dear Jed,
Sorry for late reply. This email box gets piled up... :-)

I agree that solves are faster than factorization and GMRES
use more MatVecMult, even with exact preconditioner. So I guess
PREONLY is meaning direct solve without forming any sub-space and just
one forward and backward substitutions?

Thanks,

Yan

On Wed, Apr 6, 2011 at 1:43 AM, Jed Brown <jed at 59a2.org> wrote:

> On Wed, Apr 6, 2011 at 05:27, Matthew Knepley <knepley at gmail.com> wrote:
>
>> There should be no difference since direct solves take so long.
>
>
> That is, solves are very fast compared to factorization.
>
> If you just want to check the residual, Richardson is cheaper than GMRES
> because it will require one fewer preconditioner/matrix applications.
>
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