program flip                          !!!     10-June-2005
	
!Modified From: Richard Gerber  NERSC 04/25/01

c........Flip a coin several times, and calculate heads number
c........needs the number of tries in "flip.input" 

        include 'mpif.h'
	
c........initialize MPI
        call mpi_init(ierr)
        call mpi_comm_rank(mpi_comm_world,iam,ierr)
        call mpi_comm_size(mpi_comm_world,nproc,ierr)

c........set a value for ntimes
	iheads = 0
	if (iam.eq.0) ntimes = 25000

c...... Get User Input
	if (iam.eq.0) then
		open(unit=12,file='flip.input',status='old')
		read(12,*) ntimes
		print*,' Flipping coin the default: ',ntimes,
     1                 ' times on each task.'
     		close(unit=12)
 	endif

c.......Broadcast the user's input to all tasks
	icount = 1
	iroot = 0
	mpi_type = MPI_INTEGER
	CALL MPI_BCAST(ntimes, icount, mpi_type, iroot, 
     1                 MPI_COMM_WORLD, ierror)
	
		
c.......Use random numbers to "flip" the coin
	iseed = 18*iam
	ranno = rand(iseed)
	DO i=1,ntimes
		iseed = (iseed * 100 )* ranno
		ranno = rand(iseed)
		IF(ranno.gt.0.5) iheads=iheads+1
	END DO

c.......Report the results
	PRINT *, 'Processor ',iam,' got ',iheads,' heads.'

c.......Add up all the results from all the tasks and collect on task 0
	CALL MPI_REDUCE(iheads,itotHeads,1,mpi_type,MPI_SUM,iroot,
     1                  MPI_COMM_WORLD,ierror)

c.......Calculate summary info on task 0 and print out
	IF(iam.eq.0) THEN
		pct = 100.0*FLOAT(itotHeads)/FLOAT(ntimes*nproc)
		PRINT *, 'Heads came up ',pct,' percent of the time.'
	END IF

c......close out MPI
	call mpi_finalize(ierr)

        stop
        end