[petsc-users] Fieldsplit - Schur Complement Reduction - Efficient Preconditioner for Schur Complement

[Matthew Knepley]

On Wed, Jul 25, 2018 at 4:24 AM Buesing, Henrik <
hbuesing at eonerc.rwth-aachen.de> wrote:

> Dear all,
>
> I would like to improve the iterative solver [1]. As I understand it I
> would need to improve the preconditioner for the Schur complement.
>
> How would I do that?
>

1) I always start from the exact thing (full Schur factorization with exact
solves and back off parts until I am happy)

2) Is the a11 block a good preconditioner for your Schur complement? If
not, I would start by replacing that matrix
    with something better.

  Thanks,

    Matt


> Thank you for your help!
> Henrik
>
>
>
> [1]
> -ksp_max_it 100 -ksp_rtol 1e-6 -ksp_atol 1e-50 -ksp_type fgmres -pc_type
> fieldsplit -pc_fieldsplit_type schur -pc_fieldsplit_schur_precondition a11
> -fieldsplit_p_w_ksp_type preonly -fieldsplit_S_n_ksp_type gmres
> -fieldsplit_p_w_pc_type hypre -fieldsplit_p_w_pc_hypre_type boomeramg
> -fieldsplit_S_n_pc_type hypre -fieldsplit_S_n_pc_hypre_type boomeramg
> -fieldsplit_S_n_ksp_max_it 100 fieldsplit_S_n_ksp_rtol 1e-2
>
>
> --
> Dipl.-Math. Henrik Büsing
> Institute for Applied Geophysics and Geothermal Energy
> E.ON Energy Research Center
> RWTH Aachen University
>
> Mathieustr. 10        | Tel +49 (0)241 80 49907
> 52074 Aachen, Germany | Fax +49 (0)241 80 49889
>
> http://www.eonerc.rwth-aachen.de/GGE
> hbuesing at eonerc.rwth-aachen.de
>
>

-- 
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

https://www.cse.buffalo.edu/~knepley/ <http://www.caam.rice.edu/~mk51/>
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