/*
 *  call-seq:
 *     dtable.reverse_rows  -> a_dtable
 *  
 *  Returns a copy of _dtable_ with the order of rows reversed.
 */ VALUE dtable_reverse_rows(VALUE ary)
{
   Dtable *d = Get_Dtable(ary);
   int i, j, num_cols = d->num_cols, num_rows = d->num_rows, last_row = num_rows - 1;
   VALUE new = dtable_init(dtable_alloc(cDtable), num_cols, num_rows);
   Dtable *d2 = Get_Dtable(new);
   double **src, **dest;
   src = d->ptr; dest = d2->ptr;
   for (i = 0; i < num_rows; i++) {
      for (j = 0; j < num_cols; j++) {
         dest[last_row-i][j] = src[i][j];
      }
   }
   return new;
}