[petsc-users] Nullspace issue

[Thomas Witkowski]

Am 12.06.2012 15:04, schrieb Jed Brown:
> On Tue, Jun 12, 2012 at 7:56 AM, Thomas Witkowski 
> <thomas.witkowski at tu-dresden.de 
> <mailto: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?
yes.
>
>     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.
So assume I have a basis for the null space of the system that should be 
solved. Is there any block-box solver/preconditioner approach that does 
not make use of (I)LU factorization at any point?

Thomas

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