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<p>"This email box gets piled up..."</p>
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<p>As a point of encouragement and appreciation, this is a sign of a much-used product that people are applying to increasingly-sophisticated research.</p>
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<p>Best,</p>
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<p>Peter.</p>
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<div style="FONT-SIZE: 13px; FONT-FAMILY: Tahoma">Peter G. Raeth<a></a>, Ph.D.<br>
Senior Staff Scientist<br>
Signal and Image Processing<br>
High Performance Technologies, Inc<br>
937-904-5147<br>
<a href="mailto:praeth@hpti.com" target="_blank">praeth@hpti.com</a><a></a>
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<div id="divRpF376190" style="DIRECTION: ltr"><font face="Tahoma" color="#000000" size="2"><b>From:</b> petsc-users-bounces@mcs.anl.gov [petsc-users-bounces@mcs.anl.gov] on behalf of Ryan Yan [vyan2000@gmail.com]<br>
<b>Sent:</b> Thursday, April 07, 2011 9:49 AM<br>
<b>To:</b> PETSc users list<br>
<b>Subject:</b> Re: [petsc-users] about pclu<br>
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<div>Dear Jed, <br>
Sorry for late reply. This email box gets piled up... :-)<br>
<br>
I agree that solves are faster than factorization and GMRES <br>
use more MatVecMult, even with exact preconditioner. So I guess<br>
PREONLY is meaning direct solve without forming any sub-space and just<br>
one forward and backward substitutions?<br>
<br>
Thanks,<br>
<br>
Yan <br>
<br>
<div class="gmail_quote">On Wed, Apr 6, 2011 at 1:43 AM, Jed Brown <span dir="ltr">
<<a href="mailto:jed@59a2.org" target="_blank">jed@59a2.org</a>></span> wrote:<br>
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<div class="gmail_quote">On Wed, Apr 6, 2011 at 05:27, Matthew Knepley <span dir="ltr">
<<a href="mailto:knepley@gmail.com" target="_blank">knepley@gmail.com</a>></span> wrote:<br>
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There should be no difference since direct solves take so long.</blockquote>
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<div>That is, solves are very fast compared to factorization.</div>
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<div>If you just want to check the residual, Richardson is cheaper than GMRES because it will require one fewer preconditioner/matrix applications.</div>
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