code: def linearRegressionAnalysis(series):
      
      n = safeLen(series)
      sumI = sum([i for i, v in enumerate(series) if v is not None])
      sumV = sum([v for i, v in enumerate(series) if v is not None])
      sumII = sum([i * i for i, v in enumerate(series) if v is not None])
      sumIV = sum([i * v for i, v in enumerate(series) if v is not None])
      denominator = float(n * sumII - sumI * sumI)
      if denominator == 0:
          return None
      else:
          factor = (n * sumIV - sumI * sumV) / denominator / series.step
          offset = sumII * sumV - sumIV * sumI
          offset = offset / denominator - factor * series.start
          return factor, offset
docs: Returns factor and offset of linear regression function by least
      squares method.