[petsc-users] SNESSetFunction and MatMFFDSetFunction

[Jed Brown]

Song Gao <song.gao2 at mail.mcgill.ca> writes:

> Thanks, Barry.
>
> I mean 2) providing a function that I want PETSc to difference to evaluate
> the matrix vector product.
>
> I want to make a slight modification of the matrix after PETSc evaluate the
> matrix vector product. 

Performing a matrix-vector product is not supposed to modify the matrix.
It's unlikely that you really want this.
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