Jan Blechta <[email protected]> writes: > I think that, collective PESTc routine employs MPI collective operation > (in the case that MPI implementation of Vec/Mat is used). What you are > speaking about is "logically collective" routine, e.g. > http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Mat/MatSetOption.html > > Can you confirm, Jed, whether we are correct?
"Collective" means that some communication might take place (e.g., depending on implementation). We try to be consistent in using "Neighbor-wise collective" for functions that only communicate with neighbors (e.g., MatMult), though since that convention was added later, I'm sure are places that were not updated. (Additionally, neighbor collective functions like MatMult can become synchronizing if you use -vecscatter_alltoall, for example. So the lines are blurred.) Logically collective means that the function must be called collectively to ensure a consistent parallel state, but there is not actual communication. We may check for consistency when PETSc is built in debug mode.
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