On Tue, Apr 4, 2017 at 10:10 AM, Barry Smith <[email protected]> wrote: > >> Does this mean that GAMG works for the symmetrical matrix only? > > No, it means that for non symmetric nonzero structure you need the extra > flag. So use the extra flag. The reason we don't always use the flag is > because it adds extra cost and isn't needed if the matrix already has a > symmetric nonzero structure.
BTW, if you have symmetric non-zero structure you can just set -pc_gamg_threshold -1.0', note the "or" in the message. If you want to mess with the threshold then you need to use the symmetrized flag.
