code: def _autocorr(X, X_fft):
      ca = np.fft.ifft(_multiply_complex_arr(X_fft))
      return _get_acf(X, ca)
  
imports: import math
  import numpy
  from sktime.utils.numba.njit import njit
label_desc: Use image node_id 4 for calling a global function with example usage: _autocorr(X, X_fft) and returns: _get_acf