<div dir="ltr"><div class="gmail_extra"><div class="gmail_quote">On Tue, Oct 27, 2015 at 9:10 AM, 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 dir="ltr"><div class="gmail_extra"><div class="gmail_quote"><span class="">On Tue, Oct 27, 2015 at 9:06 AM, Gary Rebt <span dir="ltr"><<a href="mailto:gary.rebt@gmx.ch" target="_blank">gary.rebt@gmx.ch</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><div style="font-family:Verdana;font-size:12.0px"><div>Dear petsc-users,</div>
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<div>While using the FEniCS package to Solve a simple Stokes' flow problem, I have run into problems with PETSc preconditioners. In particular, I would like to use ILU (no parallel version) along with GMRES to solve my linear system but the solver just hangs indefinitely at MatLUFactorNumeric_SeqAIJ_Inode without outputting anything. CPU usage is at 100% but even for a tiny system (59x59 for minimal test case), the solver does not seem to manage to push through it after 30 mins.</div>
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<div>PETSc version is 3.6 and the matrix for the minimal test case is as follows :</div>
<div><a href="http://pastebin.com/t3fvdkaS" target="_blank">http://pastebin.com/t3fvdkaS</a></div></div></div></blockquote><div><br></div></span><div>Hanging is a bug. We will check it out.</div></div></div></div></blockquote><div><br></div><div>I do not have any way to read in this ASCII. Can you output a binary version</div><div><br></div><div> -mat_view binary:mat.bin</div><div><br></div><div> Thanks,</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"><div dir="ltr"><div class="gmail_extra"><div class="gmail_quote"><span class=""><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><div style="font-family:Verdana;font-size:12.0px">
<div>It contains zero diagonal entries, has a condition number of around 1e3 but is definitely non-singular. Direct solvers manage to solve the system as well as GMRES without preconditioner (although after many iterations for a 59x59 system..).</div></div></div></blockquote><div><br></div></span><div>This will never work. Direct solvers work because they pivot away the zeros, but ILU is defined by having no pivoting.</div><div><br></div><div> Thanks,</div><div><br></div><div> Matt</div><span class=""><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><div style="font-family:Verdana;font-size:12.0px">
<div>Playing with the available options here <a href="http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/PC/PCILU.html" target="_blank">http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/PC/PCILU.html</a> did not seem to solve the issue (even after activating diagonal_fill and/or nonzeros_along_diagonal) although sometimes error 71 is returned which stands for zero pivot detected. Are there yet other options that I have not considered? The default ILU factorization in MATLAB returns satisfactory problems without errors so surely it must be possible with PETSc?</div>
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<div>As for the choice of ILU, I agree it might be suboptimal in this setting but I do need it for benchmarking purposes.</div>
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<div>Best regards,</div><span><font color="#888888">
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<div>Gary</div></font></span></div></div>
</blockquote></span></div><span class="HOEnZb"><font color="#888888"><br><br clear="all"><div><br></div>-- <br><div>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>
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</blockquote></div><br><br clear="all"><div><br></div>-- <br><div class="gmail_signature">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>
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