code: def test_first_order():
      """data and example from Zarchan, page 105-6"""
  
      lsf = LeastSquaresFilter(dt=1, order=1)
  
      xs = [1.2, 0.2, 2.9, 2.1]
      ys = []
      for x in xs:
          ys.append(lsf.update(x)[0])
  
      plt.plot(xs, c="b")
      plt.plot(ys, c="g")
      plt.plot([0, len(xs) - 1], [ys[0], ys[-1]])
  
imports: from __future__ import absolute_import, division, print_function, unicode_literals
  from math import sqrt
  import matplotlib.pyplot
  import numpy
  from numpy import dot
  import numpy.random
  from scipy.linalg import inv
  from filterpy.gh import GHFilter
  from filterpy.leastsq import LeastSquaresFilter
label_desc: Use image node_id 3 for calling a global function with example usage: test_first_order() without return types