import matplotlib.pyplot as plt
import numpy as np
x=np.linspace(-5,5)
plt.figure(figsize=(4,3))
plt.step([-5,0,0,5],[0,0,1,1],label=r"$s(u)$")
plt.plot(x,(np.tanh(x)+1)/2,"--",label=r"$g(u)$")
plt.ylim([-0.5,1.5])
plt.xlim([-5,5])
plt.xlabel('$u$')
plt.ylabel('$y$')
plt.legend(loc="lower right")
plt.grid()
plt.show()