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

[Matthew Knepley]

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
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