[petsc-dev] Problem with SNES and FieldSplit

[Jed Brown]

On Tue, Mar 15, 2011 at 23:50, Matthew Knepley <knepley at gmail.com> wrote:

> That is not what I have here. I want to change a portion, but outside of
> that I want it to fall back to a global matrix.


You were going to put your MatShell in the "pmat" slot, right? What are you
going to use for preconditioning the other blocks? If it's the same as in
"mat", you could use a MatNest for both operators and put the special sauce
in that slot of the "pmat".

If you assemble the matrix entirely monolithically (using MatSetValues
globally instead of MatSetValuesLocal on each physics separately), then we
haven't written MatSetValues_Nest yet so maybe your MatShell is the right
idea.


Related: What do people think about having MatGetSubMatrix() retain
ownership of the submatrix?
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