I'm attempting to solve a non-symmetric discretization of a 3D Poisson problem. The problem is singular. I've attached the results of KSPView from runs with ML and GAMG. When I run ML, I get convergence in 30 iterations. When I attempt to use the same settings with GAMG, I'm not getting convergence at all. The two things I notice are:<br>
<br>1. GAMG is using KSPType preonly, even though I've set it to be Richardson in my command line options.<br>2. ML only coarsens down to 4 rows while GAMG coarsens to 2. My problem is singular, and whenever I try to use LU, I get zero pivot problems. To mitigate this, I've been using Richardson with SOR on the coarse matrix. Could the smaller coarse grid size of GAMG be causing problems with SOR. If so, is there a way to put a lower limit on the coarse grid size?<br>
<br>John<br><br><div class="gmail_quote">On Thu, Mar 29, 2012 at 11:03 AM, Jed Brown <span dir="ltr"><<a href="mailto:jedbrown@mcs.anl.gov">jedbrown@mcs.anl.gov</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div class="im"><div class="gmail_quote">On Thu, Mar 29, 2012 at 09:18, John Mousel <span dir="ltr"><<a href="mailto:john.mousel@gmail.com" target="_blank">john.mousel@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>[0]PETSC ERROR: Error in external library!<br>[0]PETSC ERROR: Cannot disable floating point exceptions!</div></blockquote></div><div><br></div></div><div>Looks like something is strange with your environment because fesetenv() is returning an error. I have disabled the call if the trap mode is not changing.</div>
<br><div><a href="http://petsc.cs.iit.edu/petsc/petsc-dev/rev/352b4c19e451" target="_blank">http://petsc.cs.iit.edu/petsc/petsc-dev/rev/352b4c19e451</a></div>
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