On Thu, 13 Sep 2012, John Peterson wrote: > You get the wrong solution with boomeramg on Stokes or Navier-Stokes > because the preconditioner is singular. > > Try passing -ksp_monitor_true_residual when you run that way, and > you'll see that it's not really converging. > > http://permalink.gmane.org/gmane.comp.mathematics.libmesh.user/2187
Thanks for the update. This doesn't mesh with what I thought I remembered (correct solutions on symmetric problems, failure with asymmetry) but indeed I'm seeing failures on plain Stokes now. I don't understand the reason for the failures, though. In that thread Jed said that multigrid breaks down for indefinite systems, which sounded reasonable. (inability to invert an indefinite matrix is basically the null hypothesis) But Stokes stops being indefinite if you handle the unconstrained pressure mode, yet both the pinned pressure and the lagrange multiplier pressure formulations in our examples still fail with BoomerAMG. --- Roy ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Libmesh-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/libmesh-users
