[petsc-dev] FD matrices

Matthew Knepley knepley at gmail.com
Thu Aug 4 08:37:08 CDT 2016

On Thu, Aug 4, 2016 at 2:43 AM, Mark Adams <mfadams at lbl.gov> wrote:

> 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?

Nope, it needs some idea of connectivity to color.

> 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.

Okay, there is

  -snes_fd_color -snes_fd_color_use_mat -mat_coloring_type greedy

which takes a properly preallocated matrix.


What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener
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