Can you comment on a GASM type approach to find a solution for the null space? I notice that the null vectors that successfully make the true residual drop are only complicated in a very thin band around the interface. This band is easy to identify using a level set. Other than that, the null space vector has a low frequency variation. My thought was to break the matrix into two sub-matrices, and somehow apply GAMG as a preconditioner on the far matrix, and ILU on the interface-adjacent matrix. Is this dumb or a complete misunderstanding of GASM?
On Wed, Mar 20, 2013 at 5:08 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote: > > On Wed, Mar 20, 2013 at 5:04 PM, John Mousel <john.mousel at gmail.com>wrote: > >> I've wanted to scrap this approach for a long time, but moving away from >> these GFM-type treatments is not a choice that I've been allowed to follow >> through on for various reasons which are out of my control. > > > Unless there are some clever tricks to characterize the null space or to > keep preconditioners compatible with the null space, the folks making the > decisions might have to reconsider. It doesn't matter how sexy a method > looks if it requires a solve and that solve cannot be done efficiently. > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20130320/36ae8380/attachment-0001.html>
