MPI Basic Send/Receive

Thus the basic send (blocking!!) has become:

   MPI_Send( start, count, datatype, dest, tag, comm )

and the receive (blocking!!):

   MPI_Recv(start, count, datatype, source, tag, comm, status)

The source, tag, and count of the message actually received can be retrieved from status.

MPI_Status status;
MPI_Recv( ..., &status );
... status.MPI_TAG; ... status.MPI_SOURCE;
MPI_Get_count( &status, datatype, &count );

MPI_Get_count may be used to determine how much data of a particular type was received. Two simple collective operations (just to introduce!):

   MPI_Bcast(start, count, datatype, root, comm)
   MPI_Reduce(start, result, count, datatype,
              operation, root, comm)