The Six Fundamental MPI routines
MPI_Init (argc, argv) -- initialize
MPI_Comm_rank (comm, rank) -- find process label (rank) in group
MPI_Comm_size(comm, size) -- find total number of processes
MPI_Send (sndbuf,count,datatype,dest,tag,comm) -- send a message
MPI_Recv (recvbuf,count,datatype,source,tag,comm,status) -- receive a message
MPI_Finalize( ) -- End Up