[petsc-users] -snes_mf_operator yields "No support for this operation for this object type" in TS codes?

[Jed Brown]

Barry Smith <bsmith at mcs.anl.gov> writes:

>    Jed,
>
>     Here is the problem. 
>
> https://bitbucket.org/petsc/petsc/branch/barry/fix/even-huger-flaw-in-ts

Hmm, when someone uses -snes_mf_operator, we really just need
SNESTSFormJacobian to ignore the Amat.  However, the user is allowed to
create a MatMFFD and have their TSRHSJacobian function use MatMFFD on
their RHSFunction.  That might even be more accurate, but would require
the shift/scale.  But I'm not aware of any way in which TS can
distinguish these cases.

What if SNESComputeJacobian was aware of -snes_mf_operator and just
passed Pmat in both slots?  Or does the user sometimes need access to
the MatMFFD created by -snes_mf_operator?  (Seems like possibly, e.g.,
to adjust differencing parameters.)
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