<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Hello Matt,<div><br></div><div>I am not sure I understand your point.</div><div>I guess you mean that inside petsc only a version of Gmres working with preconditioning is not yet implemanted , Am I right ?</div><div><br></div><div>Tahar<br><div><div>Le 22 avr. 2013 à 14:12, Matthew Knepley a écrit :</div><br class="Apple-interchange-newline"><blockquote type="cite"><div dir="ltr">On Mon, Apr 22, 2013 at 7:56 AM, David Scott <span dir="ltr"><<a href="mailto:d.scott@ed.ac.uk" target="_blank">d.scott@ed.ac.uk</a>></span> wrote:<br><div class="gmail_extra"><div class="gmail_quote">
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Hello,<br>
<br>
I am working on a fluid-mechanical code to solve the two-phase Navier–Stokes equations with levelset interface capturing. I have been asked to replace the pressure calculation which uses the SOR and Jacobi iterative schemes with a Krylov subspace method. I have done this and the code is working but as I have never used PETSc before I would like to know if improvements to my code, or the run time parameters that I am using, could be made.<br>
<br>
I am using GMRES with a Block Jacobi pre-conditioner. I have tried Conjugate Gradient with a Block Jacobi pre-conditioner but it diverges. If I use GMRES for the first few thousand time steps and then swap to CG it does converge but the speed of execution is somewhat reduced.<br>
</blockquote><div><br></div><div style="">Krylov methods do not work with preconditioners. You have a Poisson problem, so as abundantly documented in the literature, you should use multigrid. The easiest thing to try is</div>
<div style=""><br></div><div style=""> -pc_type gamg -pc_gamg_agg_nsmooths 1</div><div style=""><br></div><div style=""> Thanks,</div><div style=""><br></div><div style=""> Matt</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
I have attached relevant excerpts from the code.<br>
<br>
Yours sincerely,<br>
<br>
David Scott<span class="HOEnZb"><font color="#888888"><br>
-- <br>
Dr. D. M. Scott<br>
Applications Consultant<br>
Edinburgh Parallel Computing Centre<br>
Tel. 0131 650 5921<br>
<br>
The University of Edinburgh is a charitable body, registered in<br>
Scotland, with registration number SC005336.<br>
</font></span></blockquote></div><br><br clear="all"><div><br></div>-- <br>What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.<br>
-- Norbert Wiener
</div></div>
</blockquote></div><br><div>
<span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; font-size: medium; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: medium; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: medium; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div><span class="Apple-style-span" style="font-size: 12px; "><div>--------------------------------------------</div><div>T. Amari</div><div>Centre de Physique Theorique</div><div>Ecole Polytechnique</div><div>91128 Palaiseau Cedex France</div><div>tel : 33 1 69 33 42 52</div><div>fax: 33 1 69 33 49 49</div><div><div>email: <<a href="mailto:tahar.amari@polytechnique.edu">mailto:tahar.amari@polytechnique.edu</a>></div>URL : <a href="http://www.cpht.polytechnique.fr/cpht/amari">http://www.cpht.polytechnique.fr/cpht/amari</a></div><div><br></div></span></div></div></span><br class="Apple-interchange-newline"></div></span><br class="Apple-interchange-newline"></span><br class="Apple-interchange-newline">
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