nn_activation_function.py

import numpy as np
import matplotlib.pyplot 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(-5.0, 5.0, 0.1)
y1 = step_function(x)
y2 = sigmoid(x)
y3 = relu(x)

plt.plot(x, y1, x, y2, x, y3)
plt.legend(('step function', 'sigmoid', 'ReLU'))
#plt.plot(x, y1, label='step function')
#plt.plot(x, y2)
#plt.plot(x, y3)
plt.ylim(-0.1, 5.1) # define the range of y
plt.show()