#! /usr/bin/env python3
#
def humps_derivative ( ):
  from humps import humps_fun, humps_deriv
  import matplotlib.pyplot as plt
  import numpy as np

  print ( '' )
  print ( 'humps_derivative():' )
  print ( '  Estimate the derivative of the humps function' )
  print ( '  Use user-written "derivative()" estimator.' )

  x = np.linspace ( 0.0, 2.0, 11 )
  dx = 1.0E-05
  y = derivative ( humps_fun, x, dx )
  x2 = np.linspace ( 0.0, 2.0, 201 )
  y2 = humps_deriv ( x2 )
  plt.plot ( x, y, 'ro' )
  plt.plot ( x2, y2, 'b-' )
  plt.legend ( [ 'Estimate', 'Exact' ] )
  filename = 'humps_derivative.png'
  plt.savefig ( filename )
  print ( '  Graphics saved as "' + filename + '"' )
  plt.show ( )
  return

def derivative ( f, x, dx ):
  dfdx = ( f(x+dx) - f(x-dx) ) / 2.0 / dx
  return dfdx

if ( __name__ == "__main__" ):
  humps_derivative ( )