[petsc-users] FieldSplit and Biot's poroelasticity

[Matthew Knepley]

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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