code: def _postprocess_wn(WN, analog, fs):
      wn = WN if analog else cupy.arctan(WN) * 2.0 / pi
      if len(wn) == 1:
          wn = wn[0]
      if fs is not None:
          wn = wn * fs / 2
      return wn
  
imports: import warnings
  import math
  from math import pi, prod
  import cupy
  from cupyx.scipy.special import binom
  import cupyx.scipy.special
  from cupyx.scipy.signal import _optimize
  from cupyx.scipy.signal._polyutils import roots, poly
  from cupyx.scipy.signal._lti_conversion import abcd_normalize
label_desc: Use image node_id 41 for calling a global function with example usage: _postprocess_wn(WN, analog, fs) and returns: wn