<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div><br></div> -mg_coarse_pc_factor_shift_nonzero since it is the coarse level of the multigrid that is producing the zero pivot.<div><br></div><div> Barry</div><div><br><div><div>On Apr 13, 2010, at 8:51 AM, Matthew Knepley wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite">On Tue, Apr 13, 2010 at 2:49 PM, <span dir="ltr"><<a href="mailto:tribur@vision.ee.ethz.ch">tribur@vision.ee.ethz.ch</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;"> Hi,<br> <br> using ML I got the error<br> <br> "[0]PETSC ERROR: Detected zero pivot in LU factorization"<br> <br> As recommended at <a href="http://www.mcs.anl.gov/petsc/petsc-as/documentation/troubleshooting.html" target="_blank">http://www.mcs.anl.gov/petsc/petsc-as/documentation/troubleshooting.html</a>, I tried -pc_factor_shift_nonzero but it doesn't have the desired effect using ML.<br> <br> How do I have to formulate the command line option? What does -[level]_pc_factor_shift_nonzero mean? What other parallel preconditioner could I try besides Hypre/Boomeramg or ML?<br></blockquote><div><br></div><div>This means the MG level, like 2. You can see all available options using -help.</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;"> Thanks in advance for your precious help,<br> <br> Kathrin<br> <br> <br> </blockquote></div><br><br clear="all"><br>-- <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> </blockquote></div><br></div></body></html>