subroutine exchng1( a, nx, s, e, comm1d,
     $                      nbrbottom, nbrtop )
	include "mpif.h"
	integer nx, s, e
	double precision a(0:nx+1,s-1:e+1)
	integer comm1d, nbrbottom, nbrtop
	integer status_array(MPI_STATUS_SIZE,4), ierr, req(4)
c
        call MPI_IRECV ( 
     $       a(1,s-1), nx, MPI_DOUBLE_PRECISION, nbrbottom, 0, 
     $       comm1d, req(1), ierr )
        call MPI_IRECV ( 
     $       a(1,e+1), nx, MPI_DOUBLE_PRECISION, nbrtop, 1, 
     $       comm1d, req(2), ierr )
        call MPI_ISEND ( 
     $       a(1,e), nx, MPI_DOUBLE_PRECISION, nbrtop, 0, 
     $       comm1d, req(3), ierr )
        call MPI_ISEND ( 
     $       a(1,s), nx, MPI_DOUBLE_PRECISION, nbrbottom, 1, 
     $       comm1d, req(4), ierr )
c
        call MPI_WAITALL ( 4, req, status_array, ierr )
	return
	end