/* 
  Process ID sends H[N] to Process ID+1 which stores it as H[0];
*/
  if ( id < p - 1 )
  {
    send_tag = 1;
    recv_tag = 1;

    MPI_Sendrecv ( &h[n],   1, MPI_DOUBLE, id,   send_tag, 
                   &h[0],   1, MPI_DOUBLE, id+1, recv_tag,
                   MPI_COMM_WORLD, status );
/* 
  Process ID+1 sends H[1] to process ID which stores it as H[N+1];
*/
    send_tag = 2;
    recv_tag = 2;

    MPI_Sendrecv ( &h[n+1], 1, MPI_DOUBLE, id+1, send_tag, 
                   &h[1],   1, MPI_DOUBLE, id,   recv_tag,
                   MPI_COMM_WORLD, status );
  }