Symetrix graph make a transpose and then adds them. I imagine adding two different matrices is expensive.
On Fri, Sep 16, 2022 at 8:30 PM Barry Smith <bsm...@petsc.dev> wrote: > > Mark, > > I have runs of GAMG on one and two ranks with -pc_gamg_symmetrize_graph > because the matrix is far from symmetric and some of GAMG is taking a huge > amount more time with 2 ranks than one. (While other stuff like VecNorm > shows improvement with two ranks). I've attached the two files > > Have you seen this before, is there anything that can be done about? If > going to two ranks causes almost a doubling in GAMG setup time that makes > using parallelism not useful, > > Barry > >
