code: def _compute(self):
          
          x_len = self._len
          y_len = self._order
          self._box.xmax = x_len
          self._box.ymax = y_len
  
          self._x_pos = [n / 2 for n in range(1, 2 * x_len, 2)]
          self._y_pos = [n / 2 for n in reversed(range(1, 2 * y_len, 2))]
  
          for j, serie in enumerate(self.series):
              serie.points = [(self._x_pos[i], self._y_pos[j])
                              for i in range(x_len)]
docs: Compute y min and max and y scale and set labels