Q. Functions for MPI Environment?

Int MPI_Finalize (void)

It ends the MPI environment. Any MPI function cannot be called after MPI_Finalize. Each MPI process belongs to one or more groups (which are also known as communicator). Every process is recognized by its rank (0 to group size -1) within the provided group. Primarily all processes belong to a default group known as MPI_COMM_WORLD group. Additional groups can be produced by the user as and when needed.  Now we will learn a number of functions related to communicators.

int MPI_Comm_size (MPI_Comm comm,  int *size)

It returns variable size which comprises number of processes in group comm. 

int MPI_Comm_rank (MPI_Comm comm,  int *rank)

It returns rank of calling  process in group comm.