code: def vector_angle(pairs):
      
      pairs = np.asanyarray(pairs, dtype=np.float64)
      if len(pairs) == 0:
          return np.array([])
      elif util.is_shape(pairs, (2, 3)):
          pairs = pairs.reshape((-1, 2, 3))
      elif not util.is_shape(pairs, (-1, 2, (2, 3))):
          raise ValueError('pairs must be (n,2,(2|3))!')
  
      # do the dot product between vectors
      dots = util.diagonal_dot(pairs[:, 0], pairs[:, 1])
      # clip for floating point error
      dots = np.clip(dots, -1.0, 1.0)
      # do cos and remove arbitrary sign
      angles = np.abs(np.arccos(dots))
  
      return angles
docs: Find the angles between pairs of unit vectors.
  
      Parameters
      ----------
      pairs : (n, 2, 3) float
        Unit vector pairs
  
      Returns
      ----------
      angles : (n,) float
        Angles between vectors in radians