[petsc-users] PCKSP

[Matthew Knepley]

On Tue, Jun 19, 2012 at 11:41 AM, Margarita Satraki <
margarita.satraki at gmail.com> wrote:

> 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?
>

Yes

   Matt


>
> 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
>>
>
>


-- 
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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