[petsc-users] PCKSP

[Matthew Knepley]

On Tue, Jun 19, 2012 at 11:54 AM, Margarita Satraki <
margarita.satraki at gmail.com> wrote:

> Thank you very much Matt.
>

I will just point out that this is unlikely to ever be what you want. Do
you have a particular solver
configuration in mind?

   Matt


> Margarita
>
> On 19 June 2012 18:44, Matthew Knepley <knepley at gmail.com> wrote:
>
>> 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
>>
>
>


-- 
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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