On Tue, Jun 27, 2017 at 6:36 AM, Mark Adams <[email protected]> wrote: > In talking with Garth, this will not work. > > I/we am now thinking that we should replace the MG object with Telescope. > Telescope seems to be designed to be a superset of MG. Telescope does the > processor reduction, and GAMG does as well, so we would have to reconcile > this. Does this sound like a good idea? Am I missing anything important? >
I don't think "replace" is the right word. Telescope only does process reduction. It does not do control flow for solvers, or restriction/prolongation. You can see telescope interacting with MG here https://arxiv.org/abs/1604.07163 I think more of this should be "default", in that the options are turned on if you are running GMG on a large number of procs. I also think GAMG should reuse the telescope code for doing reduction, but I am not sure how hard this is. Mark? Thanks, Matt > Mark > > On Tue, Jun 27, 2017 at 4:48 AM, Mark Adams <[email protected]> wrote: > >> Parallel coarse grid solvers are a bit broken at large scale where you >> don't want to use all processors on the coarse grid. The ideal thing might >> be to create a sub communicator, but it's not clear how to integrate this >> in (eg, check if the sub communicator exists before calling the coarse grid >> solver and convert if necessary). A bit messy. It would be nice if a >> parallel direct solver would not redistribute the matrix, but then it would >> be asking too much for it to reorder also, so we could have a crappy >> ordering. So maybe the first option would be best long term. >> >> I see we have MUMPS and PaStiX. Do either of these not redistribute if >> asked? >> > > -- 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 http://www.caam.rice.edu/~mk51/
