code: def abs_angle_diff(v_i, v_j):
      
      # compute angle distance
      dot_prod = min(max(v_i.dot(v_j), -1), 1)
      angle_diff = np.arccos(dot_prod)
      return np.abs(angle_diff)
docs: Returns the absolute value of the angle between two 3D vectors.
      
      Parameters
      ----------
      v_i : :obj:`numpy.ndarray`
          the first 3D array
      v_j : :obj:`numpy.ndarray`
          the second 3D array