[petsc-users] using PCFieldSplitGetSubKSP in c++

[Jed Brown]

On Wed, Mar 14, 2012 at 02:53, Klaij, Christiaan <C.Klaij at marin.nl> wrote:

> Thanks, no more problems after PCSetUP(). I am using petsc-dev,
> so are you saying that MatSetNullSpace() on the block matrix [A00
> A01, A10 A11] will be enough? Can/will the null space of the
> Schur complement be deduced from this? Otherwise one would still
> need to "drill down" to get Schur complement matrix, right?
>

Unfortunately, no, and I don't think it's possible to do this automatically.

Barry/Matt, this is the recurring issue of whether
MatGetSubMatrix()/MatGetSchurComplement() should have the "big" matrix
retain ownership, such that the user could decompose, set null spaces and
auxiliary operators, restore, and have PCFieldSplit and everyone else do
the right thing.
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