Thus the basic (blocking) send has become:
MPI_Send( start, count, datatype, dest, tag,
comm )
and the receive:
MPI_Recv(start, count, datatype, source, tag,
comm, status)
The source, tag, and count of the message actually received can be retrieved
from status.
Two simple collective operations:
MPI_Bcast(start, count, datatype, root, comm)
MPI_Reduce(start, result, count, datatype,
operation, root, comm)