On Wed, May 9, 2012 at 12:14 PM, Mårten Ullberg <span dir="ltr"><<a href="mailto:martenullberg@gmail.com" target="_blank">martenullberg@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">
Dear all,<br>
<br>
I am currently working on some large soil-structure interaction<br>
problems and therefor I have a finite element discretization that is<br>
going be solved in the frequency domain. This results in a symmetric,<br>
but indefinite matrix. I have not been able to find a proper method to<br>
use when solving it with PETSc.<br>
<br>
I was wondering if you guys have any recommendation on what to try,<br>
both concerning method but especially the PC? Is it recommended to use<br>
a composite PC for indefinite problems? I have tried the methods (such<br>
as MINRES, SYMMLQ) that are suggested for indefinite problems with no<br>
success. For small problems, GMRES+ASM+LU works fine, but for larger<br>
the memory consumption goes off the chart. I've also been able to use<br>
MUMPS but find it both memory and time consuming.<br>
<br>
I apologize for my lack of knowledge about iterative methods,<br></blockquote><div><br></div><div>It sounds like you are trying to solve the Helmholtz equation. No one knows</div><div>how to do this with iterative methods. Sorry the answer is so pessimistic, but</div>
<div>this is the truth unfortunately. If you can find a method you think will work, we</div><div>can tell you how to do it in PETSc.</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">
Best regards,<br>
Mårten</blockquote></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>