[petsc-users] Nullspace issue

[Jed Brown]

On Tue, Jun 12, 2012 at 7:56 AM, Thomas Witkowski <
thomas.witkowski at tu-dresden.de> wrote:

> There should be no null space from the Cahn-Hilliard equation.


You said all those boundary conditions are either Neumann or periodic. I
guess it couples to the fluid variables without any null space?


> Is there some black-box preconditioner that does not relay on LU
> factorization at some point? I know that black-box approaches are mostly
> not efficient, but I would have something I can work with.


The SVD always works and will tell you about a null space, but of course
it's very expensive.
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