code: def autocorr(x, lag=1):
      
  
      if not lag:
          return 1
      if lag < 0:
          return
      # x = np.squeeze(asarray(x))
      #     mu = x.mean()
      #     v = x.var()
      #     return ((x[:-lag]-mu)*(x[lag:]-mu)).sum()/v/(len(x) - lag)
      S = autocov(x, lag)
      return S[0, 1] / sqrt(prod(diag(S)))
docs: Sample autocorrelation at specified lag.
      The autocorrelation is the correlation of x_i with x_{i+lag}.