[petsc-dev] large cost of symmetrizing for GAMG?

[Barry Smith]

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
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