code: def _compute_value(power, wg):
      
      if power not in wg:
          p1, p2 = power
          # y power
          if p1 == 0:
              yy = wg[(0, -1)]
              wg[power] = numpy.power(yy, p2 / 2).sum() / len(yy)
          # x power
          else:
              xx = wg[(-1, 0)]
              wg[power] = numpy.power(xx, p1 / 2).sum() / len(xx)
      return wg[power]
docs: Return the weight corresponding to single power.