code: def _butter_analog_poles(n):
      """
      Poles of an analog Butterworth lowpass filter.
  
      This is the same calculation as scipy.signal.buttap(n) or
      scipy.signal.butter(n, 1, analog=True, output='zpk'), but mpmath is used,
      and only the poles are returned.
      """
      poles = []
      for k in range(-n + 1, n, 2):
          poles.append(-mpmath.exp(1j * mpmath.pi * k / (2 * n)))
      return poles
  
file_path: catboost/contrib/python/scipy/py2/scipy/signal/tests/mpsig.py
imports: from __future__ import division
label_desc: Use image node_id 5 for calling a global function with example usage: _butter_analog_poles(n) and returns: poles