Matrix free preconditioning

[Matthew Knepley]

The short answer is no. You msut know something more about your
problem. For instance, it is common to build an auxilliary matrix from
simple, analytic approximation to the operator and use that to construct
a preconditioner (this is why we always take 2 matrix args). If your
problem is elliptic, maybe you could get away with matrix-free solves in
a MG methd (but unlikely since you usually need good smoothers).

   Matt

On Tue, Oct 14, 2008 at 7:26 AM, Tim Kroeger
<tim.kroeger at cevis.uni-bremen.de> wrote:
> Dear PETSc developers,
>
> Can you give me some advice on possible/recommended choices of
> preconditioners in the case of matrix free ksp?  I create my matrix using
> MatCreateShell().  The matrix is not symmetric.  I understand that the
> typical preconditioners like ILU or JACOBI will not work since they require
> access to the matrix entries.  Is there any good precoditioner that will
> work?
>
> Best Regards,
>
> Tim
>
> --
> Dr. Tim Kroeger                                        Phone
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>
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-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which
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