first.c in detail

Let us go through first.c step by step. The program begins with an opening

MPI_Init ( &argc, &argv );

MPI_Finalize ();

All MPI programs must do that. You can have some other stuff before MPI_Init and after MPI_Finalize, but that must not be MPI. You should not assume that your job becomes parallel only after you issue the MPI_Init call though. What happens before MPI_Init and after MPI_Finalize is system dependent. LAM will start all processes on the parallel machine from the very beginning.

• Environmental enquiries
• Sending and receiving messages
• Collective communication, broadcast
• Paying homage to the master