[petsc-dev] FD matrices

[Mark Adams]

We are pushing the bounds of -snes_fd and I wanted to understand what
we can expect.  We do not use a DM.  I assume FD has to apply the
operator N times. I don't see how you can color unless we give SNES a
graph (in a DM).  Am I missing something?

If not, I could construct a symmetric matrix that would be, I think, a
"safe" graph to use for coloring. Is there an method (or example code)
to get SNES to use that for a coloring?  Like a DM constructor that
takes a graph in a Mat.