<div dir="ltr"><br><div class="gmail_extra"><br><div class="gmail_quote">2017-06-29 17:58 GMT-03:00 Matthew Knepley <span dir="ltr"><<a href="mailto:knepley@gmail.com" target="_blank">knepley@gmail.com</a>></span>:<br><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"><div class="gmail_extra"><span class="gmail-"></span><div class="gmail_quote"><div>1) For figuring out convergence issues, I would start with a smaller problem, so you can run lots of them</div></div></div></div></blockquote><div> Hi! Yes, I did start, but since they are smaller, I run with fewer processes, and with few processes they converge (as well as the big problem). It won't converge with many processes, but that isn't needed for many small problems. I can still try it and report back, anyway.<br><br></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"><div class="gmail_extra"><div class="gmail_quote"><div>2) For any questions about convergence, we need to see the output of</div><div><br></div><div> -ksp_view -ksp_monitor_true_residual -fieldsplit_1_ksp_monitor_<wbr>true_residual -ksp_converged_reason</div></div></div></div></blockquote><div>Can't provide it now, but I'll report back, too.</div><div> </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"><div class="gmail_extra"><div class="gmail_quote"><div>4) It sounds like the strength of your Schur complement preconditioner is not uniform in the size of the problem. Why</div><div> do you think LSC would be a good idea? Also, 'self' preconditioning for many equations, like Stokes, is not uniform</div><div> in problem size.</div></div></div></div></blockquote><div>I don't know what else I could solve the problem, but the size of the problem is not the issue here (yet!), otherwise, the same problem would not converge with 8 processes, but it does! The issue arises when I increase the number of processes, maintaining the global problem size. So the real question is, are the proconditiones not uniform w.r.t. the number of process, as they aren't w.r.t the size of the problem?<br></div><div>By the way, if I can't use self+LSC, how should I build the matrix to be used in the preconditioner? From my tests, it seems "a11" is a bad choice (doesn't converge).<br></div><div> <br></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"><div class="gmail_extra"><div class="gmail_quote"><div></div><div>5) What are your equations?<br></div></div></div></div></blockquote><div>The matrix is the jacobian for discrete form of the non-linear incompressible Navier-Stokes equations, given in <a href="http://mathb.in/147865">http://mathb.in/147865</a><br></div><div><br><div>About <br></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"><div class="gmail_extra"><div class="gmail_quote"><div>3) Please start with -fieldsplit_0_pc_type lu so we can just look at the Schur complement system</div></div></div></div></blockquote>and<br></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"><div class="gmail_extra"><div class="gmail_quote"><div>6) I would start with -fieldsplit_1_pc_type lu, which will test your PC matrix, and after that works, change things one at a time.<br></div></div></div></div></blockquote><div>It already works with low number of processes (same problem size)! If I manage to install and run a LU provider package that works in parallel, what new information can be obtained?<br><br></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"><div class="gmail_extra"><div class="gmail_quote"><div></div><div><br></div><div> Thanks,</div><div><br></div><div> Matt</div><span class="gmail-"><div> </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"><span class="gmail-m_2115107016963923207HOEnZb"><font color="#888888"><div>-- <br><div class="gmail-m_2115107016963923207m_-4455441475856411740gmail-m_7941801565143948590gmail-m_7828426361706057140gmail_signature">Lucas Clemente Vella<br><a href="mailto:lvella@gmail.com" target="_blank">lvella@gmail.com</a></div>
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</blockquote></span></div><span class="gmail-HOEnZb"><font color="#888888"><br><br clear="all"><div><br></div>-- <br><div class="gmail-m_2115107016963923207gmail_signature"><div dir="ltr"><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><div><br></div><div><a href="http://www.caam.rice.edu/%7Emk51/" target="_blank">http://www.caam.rice.edu/~<wbr>mk51/</a><br></div></div></div>
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</blockquote></div><br><br clear="all"><br>-- <br><div class="gmail_signature">Lucas Clemente Vella<br><a href="mailto:lvella@gmail.com" target="_blank">lvella@gmail.com</a></div>
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