[petsc-users] -pc_fieldsplit_schur_precondition

[Matthew Knepley]

On Wed, Dec 4, 2019 at 8:38 AM Cotter, Colin J <colin.cotter at imperial.ac.uk>
wrote:

> >The action of the Schur complement is always MatMult() KSPSolve()
> MatMult().
>
> OK, so when pc_fieldsplit_schur_precondition is set to full, what actually
> happens?
>

It computes the operator explicitly:


https://gitlab.com/petsc/petsc/blob/master/src/ksp/ksp/utils/schurm/schurm.c#L491

Usually you use LU, which means making B dense, then doing MatMatSolve(),
and then MatMatMult() for sparse.

  Thanks,

    Matt

-- 
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.cse.buffalo.edu/~knepley/>
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