> > Okay, there is > > -snes_fd_color -snes_fd_color_use_mat -mat_coloring_type greedy > > which takes a properly preallocated matrix. >
Which Mat will it use? Our operators matrix is a shell so it must be the PC ... If it uses the PC Mat we could take the transpose of the PC Mat, scale it by like 1.e-30, add it back into the PC Mat to get a symmetric structure, if that matters, and get a safe graph for coloring. Dan: this is easy, I will send you code today to modify "A", just use Matt's parameters above.
