Environment Routines
There are a number of important routines for monitoring
and controlling an MPI environment .
MPI_INIT(ierr),MPI_Init(&argc,&argv)
   This initialises the MPI environment e.g setting up node
id..
MPI_INITIALIZED(flag,ierr)
    This tells whether MPI_INIT has been called or not.
MPI_COMM_SIZE(comm,size.ierr)
   This returns the total number of processors in the
communicator ‘comm’
MPI_COMM_RANK(comm,rank,ierr)
    This returns the rank of the processor on which it is
called.