C-----------------------------------------------------------------------------
C MPI tutorial example code: Blocking Send/Receive
C FILE: mpi_ping.f
C AUTHOR: Blaise Barney
C LAST REVISED:
C-----------------------------------------------------------------------------
      program ping
      include 'mpif.h'

      integer numtasks, rank, dest, source, tag, ierr
      integer stat(MPI_STATUS_SIZE)
      character inmsg, outmsg
      tag = 1

      call MPI_INIT(ierr)
      call MPI_COMM_RANK(MPI_COMM_WORLD, rank, ierr)
      call MPI_COMM_SIZE(MPI_COMM_WORLD, numtasks, ierr)

      if (rank .eq. 0) then
         dest = 1
         source = 1
         outmsg = 'x'
         call MPI_SEND(outmsg, 1, MPI_CHARACTER, dest, tag, 
     &                 MPI_COMM_WORLD, ierr)
         call MPI_RECV(inmsg, 1, MPI_CHARACTER, source, tag, 
     &                 MPI_COMM_WORLD, stat, ierr)
         print *, 'Task ',rank,' sent and received from task ',dest 

      else if (rank .eq. 1) then
         dest = 0
         source = 0
         call MPI_RECV(inmsg, 1, MPI_CHARACTER, source, tag, 
     &            MPI_COMM_WORLD, stat, err)
         call MPI_SEND(outmsg, 1, MPI_CHARACTER, dest, tag, 
     &            MPI_COMM_WORLD, err)
         print *, 'Task ',rank,' sent and received from task ',dest 
      endif

      call MPI_FINALIZE(ierr)

      end