[petsc-users] Two PCs on same residual in multiplicative fashion !

[Matthew Knepley]

On Fri, Oct 26, 2012 at 12:45 PM, Abdul Hanan Sheikh <hanangul12 at yahoo.co.uk
> wrote:

> Thank you Matt, your assumption is alright. It was typo.
>
> I got this idea , yet if I want to invert P2 exactly by PCLU then how
> should I do ??
>

Read this:
http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/PC/PCKSP.html

This makes things more complicated. You can use PCOMPOSITE with
multiplicative, but its not
exactly what you have written. This is never used because its not really
effective, and doesn't make
much sense from a theory perspective. Are you sure you want to do this?

    Matt

This is indeed, but I avoid to merge(matrix product) for some reasons.
>
> Thanks again.
> Abdul
>
>   ------------------------------
> *From:* Matthew Knepley <knepley at gmail.com>
> *To:* Abdul Hanan Sheikh <hanangul12 at yahoo.co.uk>; PETSc users list <
> petsc-users at mcs.anl.gov>
> *Sent:* Friday, 26 October 2012, 18:22
> *Subject:* Re: [petsc-users] Two PCs on same residual in multiplicative
> fashion !
>
> On Fri, Oct 26, 2012 at 12:04 PM, Abdul Hanan Sheikh <
> hanangul12 at yahoo.co.uk> wrote:
>
>
> Dear Developers and members,
>
> I intend to solve system Ax=b with two preconditioners as follows:
>
> P1^{-1} P2^{-1} A x = P^{-1} P^{-1} b
>
>
> I assume you mean P1^{-1} P2^{-1} A x = P1^{-1} P2^{-1} b
>
>
>
> With this setup, I think its easiest to use PCKSP with the matrix for
> the KSP being P2. That would give you
>
>   P2^{-1} A x = P2^{-1} b
>
> Now you can precondition that solve with another PCKSP with the matrix
> for that KSP being P1, and get what you want.
>
> This seems like a strange thing since you could just merge those matrices.
>
>    Matt
>
>
>  where P1 and P2 are exclusively available as matrices.
> This might be crazy to many.
>
> I thought to start with PCCOMPOSITE but i do not think it does exactly
> what I intend.
>
> Any Idea would be appreciated.
>
> A beginner!!!
> Abdul
>
>
>
>
> --
> 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
>
>




-- 
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
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