code: def _swapsides(data):
      
      N = len(data)
      return np.concatenate((data[N//2+1:], data[0:N//2]))
docs: todo is it really useful ?
  
      Swap  sides
  
      .. doctest::
  
          >>> from spectrum import swapsides
          >>> x = [-2, -1, 1, 2]
          >>> swapsides(x)
          array([ 2, -2, -1])