code: def _fftautocorr(x):
      """Compute the autocorrelation of a real array and crop the result."""
      N = x.shape[-1]
      use_N = fftpack.next_fast_len(2 * N - 1)
      x_fft = np.fft.rfft(x, use_N, axis=-1)
      cxy = np.fft.irfft(x_fft * x_fft.conj(), n=use_N)[:, :N]
      # Or equivalently (but in most cases slower):
      # cxy = np.array([np.convolve(xx, yy[::-1], mode='full')
      #                 for xx, yy in zip(x, x)])[:, N-1:2*N-1]
      return cxy
  
imports: from __future__ import division, print_function, absolute_import
  import operator
  import warnings
  import numpy
  from scipy import fftpack, linalg, special
  from scipy._lib.six import string_types
label_desc: Use image node_id 28 for calling a global function with example usage: _fftautocorr(x) and returns: cxy