Yeah, I’ll make an issue and use a modified version of this test routine.
Does anything change if I will be using MATSCALAPACK matrices instead of the built in MATDENSE? Like I said, I will be computing Schur complements and need to use a parallel and dense matrix format. -Damyn > On Oct 26, 2023, at 10:01 AM, Matthew Knepley <knep...@gmail.com> wrote: > > On Wed, Oct 25, 2023 at 11:55 PM Damyn Chipman <damynchip...@u.boisestate.edu > <mailto:damynchip...@u.boisestate.edu>> wrote: >> Great thanks, that seemed to work well. This is something my algorithm will >> do fairly often (“elevating” a node’s communicator to a communicator that >> includes siblings). The matrices formed are dense but low rank. With >> MatCreateSubMatrix, it appears I do a lot of copying from one Mat to >> another. Is there a way to do it with array copying or pointer movement >> instead of copying entries? > > We could make a fast path for dense that avoids MatSetValues(). Can you make > an issue for this? The number one thing that would make this faster is to > contribute a small test. Then we could run it continually when putting in the > fast path to make sure we are preserving correctness. > > Thanks, > > Matt > >> -Damyn >> >>> On Oct 24, 2023, at 9:51 PM, Jed Brown <j...@jedbrown.org >>> <mailto:j...@jedbrown.org>> wrote: >>> >>> You can place it in a parallel Mat (that has rows or columns on only one >>> rank or a subset of ranks) and then MatCreateSubMatrix with all new >>> rows/columns on a different rank or subset of ranks. >>> >>> That said, you usually have a function that assembles the matrix and you >>> can just call that on the new communicator. >>> >>> Damyn Chipman <damynchip...@u.boisestate.edu >>> <mailto:damynchip...@u.boisestate.edu>> writes: >>> >>>> Hi PETSc developers, >>>> >>>> In short, my question is this: Does PETSc provide a way to move or copy an >>>> object (say a Mat) from one communicator to another? >>>> >>>> The more detailed scenario is this: I’m working on a linear algebra solver >>>> on quadtree meshes (i.e., p4est). I use communicator subsets in order to >>>> facilitate communication between siblings or nearby neighbors. When >>>> performing linear algebra across siblings (a group of 4), I need to copy a >>>> node’s data (i.e., a Mat object) from a sibling’s communicator to the >>>> communicator that includes the four siblings. From what I can tell, I can >>>> only copy a PETSc object onto the same communicator. >>>> >>>> My current approach will be to copy the raw data from the Mat on one >>>> communicator to a new Mat on the new communicator, but I wanted to see if >>>> there is a more “elegant” approach within PETSc. >>>> >>>> Thanks in advance, >>>> >>>> Damyn Chipman >>>> Boise State University >>>> PhD Candidate >>>> Computational Sciences and Engineering >>>> damynchip...@u.boisestate.edu <mailto:damynchip...@u.boisestate.edu> >> > > > -- > 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 > > https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
