[petsc-dev] Naming for PCFieldSplitSetSchurPrecondition()

[Jed Brown]

On Fri, Jun 10, 2011 at 01:01, Barry Smith <bsmith at mcs.anl.gov> wrote:

> Absolutely, by default MatGetSchurComplement() should be providing the
> diagonal block if something else is not given by the user. This way the
> fieldsplit can just call MatGetSchurComplement() and needs to have no
> special code for "if user didn't provide anything". Right?


Yes, although there is another possible option in
MatGetSchurComplement_Basic().

As currently implemented, it returns a MatSchurComplement (the real thing,
with a linear solver buried inside) as the primary and the SIMPLE
approximation as the preconditioning matrix

D - C inv(diag(A)) B


It could be made a bit smarter to figure out if MatGetDiagonal() and
MatMatMult() were implemented before proceeding down this road, otherwise
falling back to just returning the diagonal block.

In reality, that should be a run-time option, but how to we allow it to be
different for different blocks (the user might want to get multiple Schur
complements out of one matrix)?
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