!********************************************************************
! Sample program 2 : Summing up integers from 1 to 100
!                    using collective operations of MPI
! Programmer       : Makoto Nakajima
! Date             : April 2002
!********************************************************************
PROGRAM sum_1_100
	include 'mpif.h'

	!******* variable declaration *******
	integer:: partial_sum, total_sum
	integer:: int_top, int_end, int_counter

	!******* variables related MPI *******
	integer:: ierr  !return error message from MPI subroutines
	integer:: id    !identification number of each processor
	integer:: nproc !number of processors
	integer, dimension(MPI_STATUS_SIZE):: STATUS

	!******* initialize MPI system *******
	call MPI_INIT(ierr)
	call MPI_COMM_RANK(MPI_COMM_WORLD, id, ierr)
	call MPI_COMM_SIZE(MPI_COMM_WORLD, nproc, ierr)

	!******* self introduction *******
	print *, 'Hello! I am processor number ',id

	!******* summing up separately *******
	total_sum=0
	partial_sum=0
	int_top=20*id+1
	int_end=20*(id+1)
	if (id<=4) then
		do int_counter=int_top, int_end
			partial_sum=partial_sum+int_counter
		end do
	end if

	!******* calculating total sum directly by MPI_REDUCE *******
	call MPI_REDUCE(partial_sum,total_sum,1,MPI_INTEGER,MPI_SUM,0,&
		MPI_COMM_WORLD,ierr)

	!******* broadcast the total sum to all the processors *******
	call MPI_BCAST(total_sum,1,MPI_INTEGER,0,MPI_COMM_WORLD,ierr)

	!******* write out the result *******
	print *,'This is a report from processor ',id
	print *,'    my partial sum is',partial_sum
	print *,'    my total   sum is',total_sum

	!******* finalization of MPI environment
	call MPI_FINALIZE(ierr)

END PROGRAM sum_1_100