text: # draw pdf of headway distribution model according to johnsonsb
  
  import numpy as np
  from scipy.stats import johnsonsu
  from scipy.stats import johnsonsb
  import matplotlib.pyplot as plt
  fig, ax = plt.subplots(1, 1)
  
  a, b, loc, scale = -2.49, 1.49, 0.55, 0.49
  
  johnsonsu.stats(a, b,loc=loc, scale=scale, moments='mvsk')
  x = np.linspace(johnsonsu.ppf(0.01, a, b, loc=loc, scale=scale), johnsonsu.ppf(0.99, a, b,loc=loc, scale=scale), 100)
  ax.plot(x, johnsonsu.pdf(x, a, b,loc=loc, scale=scale), 'r-', lw=5, alpha=0.6, label='johnsonsu pdf')
  '''
  johnsonsb.stats(a, b,loc=loc, scale=scale, moments='mvsk')
  x = np.linspace(johnsonsb.ppf(0.01, a, b, loc=loc, scale=scale), johnsonsb.ppf(0.99, a, b,loc=loc, scale=scale), 100)
  ax.plot(x, johnsonsb.pdf(x, a, b,loc=loc, scale=scale), 'r-', lw=5, alpha=0.6, label='johnsonsb pdf')
  '''
  
  plt.show()
  