code: def _outer_distance_mod_n(ref, est, modulus=12):
      
      ref_mod_n = np.mod(ref, modulus)
      est_mod_n = np.mod(est, modulus)
      abs_diff = np.abs(np.subtract.outer(ref_mod_n, est_mod_n))
      return np.minimum(abs_diff, modulus - abs_diff)
docs: Compute the absolute outer distance modulo n.
      Using this distance, d(11, 0) = 1 (modulo 12)
  
      Parameters
      ----------
      ref : np.ndarray, shape=(n,)
          Array of reference values.
      est : np.ndarray, shape=(m,)
          Array of estimated values.
      modulus : int
          The modulus.
          12 by default for octave equivalence.
  
      Returns
      -------
      outer_distance : np.ndarray, shape=(n, m)
          The outer circular distance modulo n.