program main

!-- Process 0 sends an array of 5 real variables: x(1:5), to process 1.
!   Process 1 prints the values of the received array: y(1:5).

      use mpi
      implicit none

!--Include the mpi header file
      integer i,ierr,numprocs
      integer status(MPI_STATUS_SIZE)
      integer irc
      integer count,dest,tag
      integer my_rank,datatype,comm,source
      real x(5),y(5)

!--Initialize MPI
      call MPI_INIT( ierr )

!--Who am I? --- get my rank=my_rank
      call MPI_COMM_RANK( MPI_COMM_WORLD, my_rank, ierr )

!--How many processes in the global group?
      call MPI_COMM_SIZE( MPI_COMM_WORLD, numprocs, ierr )
      print *, "Process ", my_rank, " of ", numprocs, " is alive"

! --the common calling arguments
      count   =5   
      datatype=MPI_REAL
      tag     = 2
      comm    = MPI_COMM_WORLD

!---process 0 send data to process 1 (dest=1)
      if (my_rank == 0) then
      do i=1,5
       x(i)=float(i)
      end do
      dest    = 1
      call MPI_SEND(x(1),count,datatype, dest,tag,comm,         ierr)
      dest    = 2
      call MPI_SEND(x(1),count,datatype, dest,tag,comm,         ierr)
      end if
          
!---process 1 receives data from process 0 (source=0)
      if (my_rank == 1) then
        y=0.
        source=0
        call MPI_RECV(y(1),count,datatype, source,tag,comm,status,  ierr)
        print *,'At process ',my_rank,' y=',y, 'source=',source,' count=',count
        dest=2
        x=2*y
      call MPI_SEND(x(1),count,datatype, dest,tag,comm,         ierr)
      end if
      if (my_rank == 2) then
        y=0.
        source=0
        call MPI_RECV(y(1),count,datatype, source,tag,comm,status,  ierr)
        print *,'At process ',my_rank,' y=',y, 'source=',source,' count=',count
        source=1
        call MPI_RECV(y(1),count,datatype, source,tag,comm,status,  ierr)
        print *,'At process ',my_rank,' y=',y, 'source=',source,' count=',count
      end if

!--Finilize MPI
      call MPI_FINALIZE(irc)

      stop
      end