[petsc-users] PCKSP

[Margarita Satraki]

If I understand correctly:

For a system:
M^{-1} A x = M^{-1} b
we don't need to multiply M^{-1} A explicitly, but we solve M w = v
whenever needed.

So the Krylov method is used in order to solve that system, or equivalently
to compute the vector M^{-1} v?




On 19 June 2012 17:54, Matthew Knepley <knepley at gmail.com> wrote:

> On Tue, Jun 19, 2012 at 10:33 AM, Margarita Satraki <
> margarita.satraki at gmail.com> wrote:
>
>> Hello,
>>
>> I have difficulty understanding how PCKSP works.
>>
>> From:
>>
>> http://www.mcs.anl.gov/petsc/documentation/tutorials/Columbia04/DDandMultigrid.pdf
>> I understand that instead of using preconditioners, it uses Krylov
>> methods for the ''inner solvers''.
>>
>> What are the ''inner solvers''? Is there some kind of a subsystem that is
>> solved instead of applying a preconditioner?
>>
>
> Nope, its jsut like a PC:
>
>   M^{-1} A x = M^{-1} b
>
> where now M^{-1} instead of being an LU solve, for instance, is a Krylov
> solve.
>
>    Matt
>
>
>> Many thanks,
>>
>> Margarita
>>
>
>
>
> --
> 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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