analyze preconditioned operator?

[Matthew Knepley]

On Thu, Oct 9, 2008 at 5:25 PM, Matt Funk <mafunk at nmsu.edu> wrote:
> Hi Matt,
>
> so, the basic idea with this code is to apply the pc to each column vector of
> the matrix? Is that right?

No, that is what KSPGetExplicitOperator() does. This applies the operator in
a matrix-free way.

> Also, in your example: when is myApply actually invoked? I also looked at the
> example listed under the MatShellSetOperation reference page.

When MatMult(A) is called.

  Matt

> Is the function then actually internally called when MatShellSetOperation is
> called, or when KSPSetOperators is called or KSPSolve?
>
> The reason i am asking is that if it is called when KSPSolve called then there
> is a problem because for the analysis i never call KSPSolve directly.
>
> thanks
> matt
>
>
> On Thursday 09 October 2008, Matthew Knepley wrote:
>> On Thu, Oct 9, 2008 at 4:32 PM, Matt Funk <mafunk at nmsu.edu> wrote:
>> > mmhh,
>> >
>> > i think i am missing something. Doesn't PCApply() apply the
>> > preconditioner to a vector? So how would that work (easily) with a
>> > matrix?
>>
>> You do not apply it to the matrix. Here is a skeleton (maybe has mistakes)
>>
>> void myApply(Mat A, Vec x, Vec y) {
>>   MatShellGetContext(A, &ctx);
>>   MatMult(ctx->M, x, ctx->work);
>>   PCApply(ctx->pc, ctx->work, y);
>> }
>>
>> MatShellSetOperation(A, MATOP_MULT, myApply)
>>
>>   Matt
>>
>> > matt
>> >
>> > On Thursday 09 October 2008, Matthew Knepley wrote:
>> >> CApply().
>
>
>



-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which
their experiments lead.
-- Norbert Wiener