[petsc-users] Is PCMG a generic PC object ?

[Jed Brown]

On Fri, Dec 3, 2010 at 20:20, Vijay S. Mahadevan <vijay.m at gmail.com> wrote:

> This is fine and I am more than happy to hand these to Petsc. I do
> have the restriction/prolongation matrices explicitly but only the
> operators are matrix-free for now. So if I start off with a
> matrix-free PC operator, how exactly do I provide the shell matrix
> operators for all the other levels ?
>

PCMGSetResidual, PCMGGetSmoother and set it to whatever type you want (maybe
your custom one).


> I do not see any routine to enable this and my conclusion is that
> petsc does find it using the fine grid operator at hand using R^T*A*R
> transformation.
>

Galerkin coarse operators really need to be formed (not applied as a
product) to make sense.  PCMG calls MatPtAP(), Galerkin coarse operators
will not work unless this is implemented.  You want to provide the matrix
yourself.

Jed
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