On Fri, May 15, 2009 at 2:29 PM, Christian May <span dir="ltr"><<a href="mailto:cmay@phys.ethz.ch">cmay@phys.ethz.ch</a>></span> wrote:<br><div class="gmail_quote"><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
Hi everybody,<br>
<br>
I have trouble solving a linear equation system with PETSc 3.0.0.<br>
I tried the following combinations of solvers and preconditioners and list the results:<br>
<br>
cg+sor: Linear solve did not converge due to DIVERGED_NAN<br>
cg+bjacobi: Linear solve did not converge due to DIVERGED_INDEFINITE_PC<br>
cg+ilu: Linear solve did not converge due to DIVERGED_INDEFINITE_MAT<br>
</blockquote><div><br>1) This matrix is not SPD<br> </div><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">gmres+sor: Linear solve did not converge due to DIVERGED_NAN<br>
gmres+bjacobi:Linear solve did not converge due to DIVERGED_ITS<br>
gmres+ilu: Linear solve did not converge due to DIVERGED_ITS</blockquote><div><br>2) From DIVERGED_NAN, there is either a bug in the code, or you had some sort of floating point badness from excessive iteration. I think the former.<br>
<br>3) Run with -pc_type lu -ksp_type preonly first to test.<br><br>4) If you need parallelism with such an ill-conditioned matrix, you can try MUMPS<br><br> Matt<br><br></div><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<br>
It might be that the matrix is not positive definite, which explains some of the problems. In the last two cases it kind of works, but convergence is horribly slow and it aborts after 10000 iterations.<br>
<br>
If somebody could please have a look at the matrix and the right hand side vector, I've put them here:<br>
<a href="http://www.mayarea.de/download/small_matrix.tgz" target="_blank">http://www.mayarea.de/download/small_matrix.tgz</a><br>
The archive contains a file named A.txt, consisting of three columns<br>
i j Aij and a file b.txt with two columns i and bi.<br>
<br>
Any hint on how to solve this linear equation system (in reasonable time) is appreciated.<br>
<br>
Thanks a lot in advance!<br><font color="#888888">
<br>
Christian<br></font></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>