On Thu, Jan 19, 2023 at 11:58 AM Nicholas Arnold-Medabalimi < narno...@umich.edu> wrote:
> Hi Petsc Users > > I'm working with a distribution start forest generated by > DMPlexDistribute and PetscSFBcast and Reduce to move data between the > initial distribution and the distribution generated by DMPlex Distribute. > > I'm trying to debug some values that aren't being copied properly and > wanted to verify I understand how a redistribution SF works compared with a > SF that describes overlapped points. > > [0] 0 <- (0,7) point 0 on the distributed plex is point 7 on process > 0 on the initial distribution > [0] 1 <- (0,8) point 1 on the distributed plex is point 8 on process > 0 on the initial distribution > [0] 2 <- (0,9) > [0] 3 <- (0,10) > [0] 4 <- (0,11) > > [1] 0 <- (1,0) point 0 on the distributed plex is point 0 on process > 1 on the initial distribution > [1] 1 <- (1,1) > [1] 2 <- (1,2) > [1] 3 <- (0,0) point 3 on the distributed plex is point 0 on process > 0 on the initial distribution > [1] 4 <- (0,1) > [1] 5 <- (0,2) > > my confusion I think is how does the distributionSF inform of what cells > will be leafs on the distribution? > I should eventually write something to clarify this. I am using SF in (at least) two different ways. First, there is a familiar SF that we use for dealing with "ghost" points. These are replicated points where one process is said to "own" the point and another process is said to hold a "ghost". The ghost points are leaves in the SF which point back to the root point owned by another process. We call this the pointSF for a DM. Second, we have a migration SF. Here the root points give the original point distribution. The leaf points give the new point distribution. Thus a PetscSFBcast() pushes points from the original to new distribution, which is what we mean by a migration. Third, instead of point values, we might want to communicate fields over those points. For this we make new SFes, where the numbering does not refer to points, but rather to dofs. Does this make sense? Thanks, Matt > Sincerely > Nicholas > > -- > Nicholas Arnold-Medabalimi > > Ph.D. Candidate > Computational Aeroscience Lab > University of Michigan > -- 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/>