[petsc-users] about pclu

[Raeth, Peter]

"This email box gets piled up..."



As a point of encouragement and appreciation, this is a sign of a much-used product that people are applying to increasingly-sophisticated research.





Best,



Peter.



Peter G. Raeth, Ph.D.
Senior Staff Scientist
Signal and Image Processing
High Performance Technologies, Inc
937-904-5147
praeth at hpti.com<mailto:praeth at hpti.com>
________________________________
From: petsc-users-bounces at mcs.anl.gov [petsc-users-bounces at mcs.anl.gov] on behalf of Ryan Yan [vyan2000 at gmail.com]
Sent: Thursday, April 07, 2011 9:49 AM
To: PETSc users list
Subject: Re: [petsc-users] about pclu

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<mailto:jed at 59a2.org>> wrote:
On Wed, Apr 6, 2011 at 05:27, Matthew Knepley <knepley at gmail.com<mailto: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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