code: def computeA(self, j, timeSeries):
          
          seasonLength = self.get_parameter("seasonLength")
          A_j = 0
          for i in range(seasonLength):
              A_j += timeSeries[(seasonLength * (j)) + i][1]
          return A_j / seasonLength
docs: Calculates A_j. Aj is the average value of x in the jth cycle of your data
  
          :return:    A_j
          :rtype:     numeric