[petsc-users] Any changes in ML usage between 3.1-p8 -> 3.3-p6?

[Jozsef Bakosi]

> 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