[petsc-users] PCKSP

[Margarita Satraki]

For my problem (incompressible nonlinear elasticity) pcksp seemed to work
ok with gmres and even better with fgmres.
The best option was to use LU as PC but this requires a lot of memory.

Why do you think that would not be a good option?

Margarita


On 19 June 2012 19:00, Matthew Knepley <knepley at gmail.com> wrote:

> 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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