docs: def validate_basic_smoother_resid():
      """Compare residuals."""
      x, y = sort_data(*smoother_friedman82.build_sample_smoother_problem_friedman82())
      plt.figure()
      for span in smoother.DEFAULT_SPANS:
          my_smoother = smoother.perform_smooth(x, y, span)
          _friedman_smooth, resids = run_friedman_smooth(x, y, span)  # pylint: disable=unused-variable
          plt.plot(x, my_smoother.cross_validated_residual, '.-',
                   label='pyace span = {0}'.format(span))
          plt.plot(x, resids, '.-', label='Friedman span = {0}'.format(span))
      finish_plot()