<html><head><meta http-equiv="Content-Type" content="text/html; charset=us-ascii"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div class=""><br class=""></div> What KSP are you using? DIVERGED_BREAKDOWN is very rare for KSPGMRES. If you are using one of its lesser cousins like bcgs you might consider switching to bcgsl or gmres.<div class=""><br class=""></div><div class=""> I assume because of boundary conditions or the discretization you do not have symmetric positive definite and thus cannot use CG.</div><div class=""><br class=""></div><div class=""> Barry</div><div class=""><br class=""><div><br class=""><blockquote type="cite" class=""><div class="">On Oct 12, 2022, at 2:00 PM, Matthew Knepley <<a href="mailto:knepley@gmail.com" class="">knepley@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class=""><div dir="ltr" class="">On Wed, Oct 12, 2022 at 1:38 PM Alfredo J Duarte Gomez <<a href="mailto:aduarteg@utexas.edu" class="">aduarteg@utexas.edu</a>> wrote:<br class=""></div><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr" class=""><div class="">Good morning PETSC users,</div><div class=""><br class=""></div><div class="">I have a current solver that requires the solution of a Laplace equation to be reused for all future time steps.</div><div class=""><br class=""></div><div class="">The configuration is axisymmetric with Dirichlet BCs at the top and bottom boundaries, and Zero Neumman conditions at the axis and far field. The grid is curvilinear and structured. <br class=""></div><div class=""><br class=""></div><div class="">So far I have been using PCHYPRE boomeramg as the preconditioner, which often works well, but I have also experienced DIVERGED_BREAKDOWN on many occasions. When I use direct solver PCMUMPS it always produces a satisfactory answer, which gives me confidence that the solution exists for the given grid in all these configurations where boomeramg fails.</div></div></blockquote><div class=""><br class=""></div><div class="">I do not know why Hypre is breaking down. Did you try ML or GAMG? They are easier to diagnose I think.</div><div class=""><br class=""></div><div class=""> Thanks,</div><div class=""><br class=""></div><div class=""> Matt</div><div class=""> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr" class=""><div class="">I am looking for recommendations on other preconditioners to try in this problem that can produce a solution faster than PCMUMPS, or recommendations on which parameters to adjust on boomeramg.</div><div class=""><br class=""></div><div class="">Thank you,<br class=""></div><div class=""><br class=""></div><div class=""><br class="">-- <br class=""><div dir="ltr" class=""><div dir="ltr" class=""><div class=""><div dir="ltr" class=""><font face="arial, sans-serif" class="">Alfredo Duarte</font><div class=""><font face="arial, sans-serif" class="">Graduate Research Assistant</font></div><div class=""><font face="arial, sans-serif" class="">The University of Texas at Austin</font></div></div></div></div></div></div></div>
</blockquote></div><br clear="all" class=""><div class=""><br class=""></div>-- <br class=""><div dir="ltr" class="gmail_signature"><div dir="ltr" class=""><div class=""><div dir="ltr" class=""><div class=""><div dir="ltr" class=""><div class="">What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.<br class="">-- Norbert Wiener</div><div class=""><br class=""></div><div class=""><a href="http://www.cse.buffalo.edu/~knepley/" target="_blank" class="">https://www.cse.buffalo.edu/~knepley/</a><br class=""></div></div></div></div></div></div></div></div>
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