code: def _FC_LocalSimple_mean1_tauresrat(X, acfz):
      # Change in correlation length after iterative differencing.
      if len(X) < 2:
          return 0
      res = _local_simple_mean(X, 1)
      mean = np.mean(res)
  
      nfft = int(np.power(2, np.ceil(np.log(len(res)) / np.log(2))))
      fft = np.fft.fft(res - mean, n=nfft)
      ac = _autocorr(res, fft)
  
      return _ac_first_zero(ac) / acfz
  
imports: import math
  import numpy
  from sktime.utils.numba.njit import njit
label_desc: Use image node_id 31 for calling a global function with example usage: _FC_LocalSimple_mean1_tauresrat(X, acfz) and returns: unknown, int