[petsc-dev] MatSetColoring

[Peter Brune]

On Fri, May 17, 2013 at 4:09 PM, Jed Brown <jedbrown at mcs.anl.gov> wrote:

> Peter Brune <prbrune at gmail.com> writes:
>
> > Yeah it was pretty easy to break in TS..  I thought that I might be going
> > in circles here.
> >
> >
> >>
> >> It's probably worth risking the low-probability of a user depending on
> >> the parameter being ignored in exchange for being able to fix this
> >> inconvenience in petsc-3.4.
> >>
> >
> > What exactly do you mean by this?  I can "fix it" for the TS case by
> > replacing the error-out on the parameter with a type compare, but for a
> > general user context that's not a PetscObject it's more dicey.  We could
> > zero it out explicitly when setting snes_fd_coloring from options
>
> If at all possible, I think it _should_ be zeroed by -snes_fd_coloring.
>
> > and expect users to do the right thing.
>
> That was the point of my comment.  We don't think they are in the same
> position as -snes_fd_coloring, but all their old code either passed NULL
> or passed a valid MatFDColoring or passed NULL, and it's not very useful
> to write new code that passes non-NULL.
>

The example that caused me to go into this in the first place was
snes/examples/tutorials/ex45.c, which a) set the user context, then
manually set the Jacobian func to SNESComputeJacobianDefaultColor and b)
seems to have disappeared, so I'm on board with this.

- Peter
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