subroutine exchng1(a, nx, s, e, comm1d, nbrbottom, nbrtop)
use mpi
integer nx, s, e, comm1d, nbrbottom, nbrtop
double precision a(0:nx+1,s-1:e+1)
integer ierr
call MPI_SEND(a(1,e), nx, MPI_DOUBLE_PRECISION, &
nbrtop, 0, comm1d, ierr)
call MPI_RECV(a(1,s-1), nx, MPI_DOUBLE_PRECISION, &
nbrbottom, 0, comm1d, MPI_STATUS_IGNORE, ierr)
call MPI_SEND(a(1,s), nx, MPI_DOUBLE_PRECISION, &
nbrbottom, 1, comm1d, ierr)
call MPI_RECV(a(1,e+1), nx, MPI_DOUBLE_PRECISION, &
nbrtop, 1, comm1d, MPI_STATUS_IGNORE, ierr)
return
end