[petsc-dev] Preconditioner for Schur complement (pcfieldsplit)

[Jed Brown]

On Tue, Mar 29, 2011 at 13:12, Thomas Witkowski <
thomas.witkowski at tu-dresden.de> wrote:

> PCFieldsplitSchurPrecondition seems to do what I want. But how to create
> the matrix for the preconditioner? I'm a little bit confused about it
> because the matrix/operator S acts on an index range that does not start
> from 0 and is not continuous, because each rank owns only some parts of the
> interior domain boundaries.


We do not currently have a way to set attributes on a "submatrix" that you
will extract in the future. You can implement MatGetSubMatrix to return your
special matrix for that block when called with that pair of ISs. Or you can
use MatNest for the preconditioning matrix, it is frequently a good storage
format when doing fieldsplit and you can use it unintrusively.
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