<div dir="ltr"><div class="gmail_extra"><div class="gmail_quote">On Tue, Jun 2, 2015 at 4:00 PM, Justin Chang <span dir="ltr"><<a href="mailto:jychang48@gmail.com" target="_blank">jychang48@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>MTH did not converge with the default -ksp_rtol 1e-6 so I had to raise the tolerance to 1e-5 in order to get a solution. Attached are the outputs for TH and MTH<br></div></div></blockquote><div><br></div><div>This really looks like it was never solving this system.</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></div>Last one with the svd did not work with the way the AMG PC was hard-coded into FEniCS. Here's the list of preconditioners my installation of FEniCS supports:<br><br>Preconditioner | Description <br>---------------------------------------------------------------<br>default | default preconditioner <br>ilu | Incomplete LU factorization <br>icc | Incomplete Cholesky factorization <br>sor | Successive over-relaxation <br>petsc_amg | PETSc algebraic multigrid <br>jacobi | Jacobi iteration <br>bjacobi | Block Jacobi iteration <br>additive_schwarz | Additive Schwarz <br>amg | Algebraic multigrid <br>hypre_amg | Hypre algebraic multigrid (BoomerAMG) <br>hypre_euclid | Hypre parallel incomplete LU factorization<br>hypre_parasails | Hypre parallel sparse approximate inverse <br>none | No preconditioner <br><br>I would need to change a few things here and there if we really insisted on seeing if svd works.<br></div><div class="HOEnZb"><div class="h5"><div class="gmail_extra"><br><div class="gmail_quote">On Tue, Jun 2, 2015 at 3:00 PM, Jed Brown <span dir="ltr"><<a href="mailto:jed@jedbrown.org" target="_blank">jed@jedbrown.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><span>Justin Chang <<a href="mailto:jychang48@gmail.com" target="_blank">jychang48@gmail.com</a>> writes:<br>
<br>
> I originally solve that example problem using LU.<br>
<br>
</span>I'd like to learn why LU didn't notice that the system is singular.<br>
(The checks are not reliable, but this case should be pretty obviously<br>
bad.)<br>
<span><br>
> But when I solve this one:<br>
><br>
> <a href="http://fenicsproject.org/documentation/dolfin/1.5.0/python/demo/documented/stokes-iterative/python/documentation.html" target="_blank">http://fenicsproject.org/documentation/dolfin/1.5.0/python/demo/documented/stokes-iterative/python/documentation.html</a><br>
><br>
> By simply running their code as is for TH and adding the one like I<br>
> mentioned for MTH, I get the following outputs when I pass in -ksp_monitor<br>
> -ksp_view and -log_summary<br>
<br>
</span>Thanks, Justin. Could you please run with<br>
<br>
-ksp_type gmres -ksp_gmres_restart 1000 -ksp_monitor_true_residual -ksp_monitor_singular_value<br>
<br>
Also, can you run a tiny problem size (like less than 1000 dofs) with<br>
<br>
-pc_type svd -pc_svd_monitor<br>
<br>
Thanks.<br>
</blockquote></div><br></div>
</div></div></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>
</div></div>