On Tue, Jun 19, 2012 at 12:13 PM, Margarita Satraki <span dir="ltr"><<a href="mailto:margarita.satraki@gmail.com" target="_blank">margarita.satraki@gmail.com</a>></span> wrote:<br><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
For my problem (incompressible nonlinear elasticity) pcksp seemed to work ok with gmres and even better with fgmres.<br>The best option was to use LU as PC but this requires a lot of memory.<br></blockquote><div><br></div>
<div>You can just use</div><div><br></div><div> -ksp_type preonly</div><div> -pc_type lu</div><div><br></div><div>to get a direct solution. Its not clear why you would want PCKSP.</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Why do you think that would not be a good option?<br></blockquote><div><br></div><div>Incompressible elasticity has a constraint, so it is a saddle point system. We would recommend using</div><div>PC_FIELDSPLIT, splitting into blocks for the displacement and pressure. You can do this automatically</div>
<div>using -pc_fieldsplit_detect_saddle_point.</div><div><br></div><div>We would also proba bly recommend using AMG (ML, or GAMG, etc.) for the elastic block. You have to provide</div><div>the near null modes (6 rot+trans), but there are examples of this from Mark Adams and me.</div>
<div><br></div><div> Matt</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Margarita<br><br><br><div class="gmail_quote">On 19 June 2012 19:00, 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:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div>On Tue, Jun 19, 2012 at 11:54 AM, Margarita Satraki <span dir="ltr"><<a href="mailto:margarita.satraki@gmail.com" target="_blank">margarita.satraki@gmail.com</a>></span> wrote:<br></div><div class="gmail_quote">
<div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Thank you very much Matt.<br></blockquote><div><br></div></div><div>I will just point out that this is unlikely to ever be what you want. Do you have a particular solver</div><div>configuration in mind?</div><div><br></div>
<div>
Matt</div><div><div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Margarita<br><br><div class="gmail_quote">On 19 June 2012 18:44, 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:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div>On Tue, Jun 19, 2012 at 11:41 AM, Margarita Satraki <span dir="ltr"><<a href="mailto:margarita.satraki@gmail.com" target="_blank">margarita.satraki@gmail.com</a>></span> wrote:<br>
</div><div class="gmail_quote"><div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
If I understand correctly:<br><br>For a system:<br>M^{-1} A x = M^{-1} b<br>we don't need to multiply M^{-1} A explicitly, but we solve M w = v whenever needed.<br><br>So the Krylov method is used in order to solve that system, or equivalently to compute the vector M^{-1} v?<br>
</blockquote><div><br></div></div><div>Yes</div><div><br></div><div> Matt</div><div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><br><div class="gmail_quote">
On 19 June 2012 17:54, 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:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div><div>On Tue, Jun 19, 2012 at 10:33 AM, Margarita Satraki <span dir="ltr"><<a href="mailto:margarita.satraki@gmail.com" target="_blank">margarita.satraki@gmail.com</a>></span> wrote:<br>
</div></div><div class="gmail_quote"><div><div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Hello,<br><br>I have difficulty understanding how PCKSP works.<br><br>From:<br><a href="http://www.mcs.anl.gov/petsc/documentation/tutorials/Columbia04/DDandMultigrid.pdf" target="_blank">http://www.mcs.anl.gov/petsc/documentation/tutorials/Columbia04/DDandMultigrid.pdf</a><br>
I understand that instead of using preconditioners, it uses Krylov methods for the ''inner solvers''.<br><br>What are the ''inner solvers''? Is there some kind of a subsystem that is solved instead of applying a preconditioner?<br>
</blockquote><div><br></div></div></div><div>Nope, its jsut like a PC:</div><div><br></div><div> M^{-1} A x = M^{-1} b</div><div><br></div><div>where now M^{-1} instead of being an LU solve, for instance, is a Krylov solve.</div>
<div>
<br></div><div> Matt</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Many thanks,<br><br>Margarita<span><font color="#888888"><br>
</font></span></blockquote></div><span><font color="#888888"><br><br clear="all"><span><font color="#888888"><span><font color="#888888"><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<br>
</font></span></font></span></font></span></blockquote></div><span><font color="#888888"><br>
</font></span></blockquote></div></div><span><font color="#888888"><div><div><br><br clear="all"><span class="HOEnZb"><font color="#888888"><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<br>
</font></span></div></div></font></span></blockquote></div><span class="HOEnZb"><font color="#888888"><br>
</font></span></blockquote></div></div></div><span class="HOEnZb"><font color="#888888"><div><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<br>
</div></div></font></span></blockquote></div><br>
</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<br>