MPI_COMM_RANK

MPI_COMM_RANK(comm, rank) 
[ IN comm] communicator (handle) 
[ OUT rank] rank of the calling process in group of comm (integer) 

Code            int MPI_Comm_rank(MPI_Comm comm, int *rank)
This call returns the ``rank'' of the current process within a communicator. Every communicator can be considered to contain a group of processes, each of which has a unique integer ``rank'' identifier starting from 0 and increasing (0,1,2,3,...).