[petsc-dev] TSComputeIJacobian() no IJacobian function provided and no IMEX slow?

[Jed Brown]

Barry Smith <bsmith at mcs.anl.gov> writes:
> Not that axpy is DIFFERENT_NONZERO_PATTERN which means a very slow
> MatAXPY(). If I understand things correctly after the first time
> through here *A will have a nonzero pattern at least as big as Arhs?

Yes, but what happens when Arhs is reassembled with a different nonzero
pattern?

> If so how can the code be organized so that slow MatAXPY() is not used
> for an eternity and switches to using subset for much faster
> performance?

We just need a reliable way to know when the nonzero pattern of Arhs
changes.
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