import numpy as np
import matplotlib.pylab as plt

def step_function(x):
    return np.array(x > 0, dtype=np.int)

def sigmoid(x):
    return 1 / (1 + np.exp(-x))

def relu(x):
    return np.maximum(0, x)

x = np.arange(-6, 6, 1)
y = relu(x)
plt.plot(x, y)
plt.ylim(-1, 5)
plt.show()
