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">jed@59a2.org</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;"><div dir="ltr"><div class="im"><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>
<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
There should be no difference since direct solves take so long.</blockquote></div><br></div><div>That is, solves are very fast compared to factorization.</div><div><br></div><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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