[petsc-users] FieldSplit and Biot's poroelasticity

[Karin&NiKo]

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.

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
>
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