Thanks for your help, but unfortunately I am still not clear.
> You are right Dave, FUNNELED allows the application to have multiple
> threads but only the man thread calls MPI.
My understanding is that even if I use SINGLE or MPI_Init, I can still
have multiple threads if I use OpenMP PARALLEL directive, and only
the main thread makes MPI calls. Am I correct?
> An OpenMP/MPI hybrid program that makes MPI calls only in between parallel
> sections is usually a FUNNELED user of MPI
For an OpenMP/MPI hybrid program, if I only want to make MPI calls using
the main thread, ie., only in between parallel sections, can I just use
SINGLE or MPI_Init? What's the benefit of FUNNELED?