[petsc-users] FieldSplit and Biot's poroelasticity

[Karin&NiKo]

Thank you very much Matt.
I have given selfp a try and I am even more convienced that the pressure
mass matrix must be implemented!

Regards,
Nicolas

2016-12-14 15:24 GMT+01:00 Matthew Knepley <knepley at gmail.com>:

> On Wed, Dec 14, 2016 at 2:17 AM, Karin&NiKo <niko.karin at gmail.com> wrote:
>
>> Lawrence, Matt,
>>
>> I really do share your point.
>> Nevertheless there are sometimes good reasons to do things  "not the best
>> way they should be done", at least in a first time (here PETSc is used
>> within a huge fortran-based general purpose finite element solver and build
>> and extract the pressure mass matrix is not a straightforward task).
>> In the present case, I am looking for "the less worst approach" out of
>> the fieldsplit built-in preconditioners.
>> And I consider this is not an uninteresting question.
>>
>
> Depending on how diagonally dominant things are, 'selfp' could be an
> acceptable replacement for using the mass matrix:
>
>   http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/PC/
> PCFieldSplitSetSchurPre.html#PCFieldSplitSetSchurPre
>
>     Matt
>
>
>> Best regards,
>> Nicolas
>>
>> 2016-12-13 19:41 GMT+01:00 Matthew Knepley <knepley at gmail.com>:
>>
>>> On Tue, Dec 13, 2016 at 10:50 AM, Karin&NiKo <niko.karin at gmail.com>
>>> wrote:
>>>
>>>> Dear Petsc-gurus,
>>>>
>>>> I am solving Biot's poroelasticity problem :
>>>>  [image: Images intégrées 1]
>>>>
>>>> I am using a mixed P2-P1 finite element discretization.
>>>>
>>>> I am using the fieldsplit framework to solve the linear systems. Here
>>>> are the options I am using :
>>>> -pc_type fieldsplit
>>>> -pc_field_split_type schur
>>>> -fieldsplit_0_pc_type gamg
>>>> -fieldsplit_0_pc_gamg_threshold -1.0
>>>> -fieldsplit_0_ksp_type gmres
>>>> -fieldsplit_0_ksp_monitor
>>>> -fieldsplit_1_pc_type sor
>>>> -fieldsplit_1_ksp_type gmres
>>>> -pc_fieldsplit_schur_factorization_type upper
>>>>
>>>>
>>>> By increasing the mesh size, I get increasing numbers of outer
>>>> iterations.
>>>>
>>>> According to your own experience, among all the features of fieldsplit,
>>>> was is the "best" set of preconditioners for this rather classical problem
>>>>  in order to get an extensible solver (I would like to solve this problem
>>>> on some tens millions of unknowns of some hundreds of procs)?
>>>>
>>>
>>> Lawrence is right that you should construct the right preconditioner
>>> matrix for the Schur complement, and its probably just something like I +
>>> \Delta with
>>> the correct multipliers. Without the mass matrix, it will likely be
>>> quite bad. It should not take much time to code that up since you already
>>>  have the mass
>>> matrix from your c_0 p term.
>>>
>>>   Matt
>>>
>>>
>>>> Thanks,
>>>> Nicolas
>>>>
>>>
>>>
>>>
>>> --
>>> 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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