Lambda를 활용한 Activate Function

import matplotlib.pyplot as plt
import numpy as np
%matplotlib inline


x = list(range(-100,100))

step_y = list(map(lambda a : 1 if a>0 else 0, x))
sign_y = list(map(lambda a : 1 if a>0 else -1, x))
sign_y[100] = 0 #lambda는 elif가 없음.
sigmoid_y = list(map(lambda a : 1 / (1 + np.exp(-a)), (x)))
relu_y = list(map(lambda a : a if a>0 else 0, x))

fig, (ax1, ax2, ax3, ax4) = plt.subplots(figsize = (18, 4), ncols = 4)
ax1.plot(x, step_y)
ax1.set_title('step function')
ax2.plot(x, sign_y)
ax2.set_title('sign function')
ax3.plot(x, sigmoid_y)
ax3.set_title('sigmoid function')
ax4.plot(x, relu_y)
ax4.set_title('relu function')