code: def optimal_test():
      def fx(x):
          return 0.1 * x**2 + 3 * x - 4
  
      g, h, k = optimal_noise_smoothing(0.2)
      f = GHKFilter(-4, 0, 0, 1, g, h, k)
  
      ys = []
      zs = []
      for i in range(100):
          z = fx(i) + randn() * 10
          f.update(z)
          ys.append(f.x)
          zs.append(z)
  
      plt.plot(ys)
      plt.plot(zs)
  
file_path: filterpy/filterpy/gh/tests/test_gh.py
imports: from __future__ import absolute_import, division, print_function, unicode_literals
  from filterpy.common import Saver
  from filterpy.gh import GHFilter, GHKFilter, least_squares_parameters, optimal_noise_smoothing, GHFilterOrder
  from numpy import array
  from numpy.random import randn
  import matplotlib.pyplot
label_desc: Use image node_id 4 for calling a global function with example usage: optimal_test() and returns: unknown