program group 
	include 'mpif.h' 
	integer NPROCS 
	parameter(NPROCS=8) 
	Integer rank, new_rank, sendbuf, recvbuf, numtasks 
	integer ranks1(4), ranks2(4), ierr 
	integer orig_group, new_group, new_comm 
	data ranks1 /0, 1, 2, 3/, ranks2 /4, 5, 6, 7/ 
	call MPI_INIT(ierr) 
	call MPI_COMM_RANK(MPI_COMM_WORLD, rank, ierr) 
	call MPI_COMM_SIZE(MPI_COMM_WORLD, numtasks, ierr) 
	if (numtasks .ne. NPROCS) then 
	print *, 'Must specify MPROCS= ',NPROCS,' Terminating.' 
	call MPI_FINALIZE(ierr) 
	stop 
	endif 
	sendbuf = rank 
C Extract the original group handle 
	call MPI_COMM_GROUP(MPI_COMM_WORLD, orig_group, ierr) 
C Divide tasks into two distinct groups based upon rank 
	if (rank .lt. NPROCS/2) then 
	call MPI_GROUP_INCL(orig_group, NPROCS/2, ranks1, 
     & new_group, ierr) 
	else 
	call MPI_GROUP_INCL(orig_group, NPROCS/2, ranks2, 
     & new_group, ierr) 
	endif 
	call MPI_COMM_CREATE(MPI_COMM_WORLD, new_group, 
     & new_comm, ierr) 
	call MPI_ALLREDUCE(sendbuf, recvbuf, 1, MPI_INTEGER,  MPI_SUM, 
     & new_comm, ierr) 
	call MPI_GROUP_RANK(new_group, new_rank, ierr) 
	print *, 'rank= ',rank,' newrank= ',new_rank,' recvbuf= ', recvbuf 
	call MPI_FINALIZE(ierr) 
	end