code: def footrule_dist(params1, params2=None):
      r
      assert params2 is None or len(params1) == len(params2)
      ranks1 = rankdata(params1, method="average")
      if params2 is None:
          ranks2 = np.arange(1, len(params1) + 1, dtype=float)
      else:
          ranks2 = rankdata(params2, method="average")
      return np.sum(np.abs(ranks1 - ranks2))