> Mark F. Adams mark.adams at columbia.edu > Wed Apr 17 14:25:04 CDT 2013 > > 2) If you get "Indefinite PC" (I am guessing from using CG) it is because the > preconditioner > really is indefinite (or possible non-symmetric). We improved the checking > for this in one > of those releases. > > AMG does not guarantee an SPD preconditioner so why persist in trying to use > CG? > > > AMG is positive if everything is working correctly. > > Are these problems only semidefinite? Singular systems can give erratic > behavior.
It is a Laplace operator from Galerkin finite elements. And the PC is fine on ranks 1, 2, 3, and 5 -- indefinite only on 4. I think we can safely say that the same PC should be positive on 4 as well. Can you guys please CC jbakosi at lanl.gov? Thanks, J
