code: def transFringe(beta=None, rho=None):
      
      m = np.eye(6, 6, dtype=np.float64)
      if None in (beta, rho):
          print("warning: 'theta', 'rho' should be positive float numbers.")
          return m
      else:
          m[1, 0] = np.tan(beta) / rho
          m[3, 2] = -np.tan(beta) / rho
          return m
docs: Transport matrix of fringe field
  
      :param beta: angle of rotation of pole-face in [RAD]
      :param rho: bending radius in [m]
      :return: 6x6 numpy array