docs: def validate_known_curve():
      """Validate on a sin function."""
      plt.figure()
      N = 100
      x = numpy.linspace(-1, 1, N)
      y = numpy.sin(4 * x)
      smoother.DEFAULT_BASIC_SMOOTHER = smoother.BasicFixedSpanSmootherSlowUpdate
      smooth = smoother.perform_smooth(x, y, smoother_cls=supersmoother.SuperSmoother)
      plt.plot(x, smooth.smooth_result, label='Slow')
      smoother.DEFAULT_BASIC_SMOOTHER = smoother.BasicFixedSpanSmoother
      smooth = smoother.perform_smooth(x, y, smoother_cls=supersmoother.SuperSmoother)
      plt.plot(x, smooth.smooth_result, label='Fast')
      plt.plot(x, y, '.', label='data')
      plt.legend()
      plt.show()