import numpy as np
import matplotlib.pyplot as plt

f= lambda x: 0.1*x**5-0.2*x**3+0.1*x-0.2
df= lambda x: 0.5*x**4-0.6*x**2+0.1

h=0.1
x=np.linspace(-0.3,0.3)
plt.plot(x,df(x),'-k')

#forward differences
diff1= (f(x+h)-f(x))/h
plt.plot(x,diff1,'-b')

#backward differences
diff1= (f(x)-f(x-h))/h
plt.plot(x,diff1,'-r')

#central differences
diff1= (f(x+h)-f(x-h))/(2*h)
plt.plot(x,diff1,'-g')


plt.xlabel('x')
plt.ylabel('y')
plt.legend(["Equat.","FFD","BFD","CFD"])
plt.grid()
plt.show