激活函數sigmoid和tanh

1.sigmoid函數也稱爲S型函數，該函數將變量全部映射到(0,1)區間。函數表達式如下所示：

import numpy as np
import matplotlib.pyplot as plt

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

x = np.arange(-10,10,0.01)
y = sigmoid(x)
plt.plot(x,y,linewidth = 3,label = "Sigmoid")
plt.grid()
plt.legend()
plt.show()

2.tanh函數稱爲雙曲正切函數，由雙曲正弦和雙曲餘弦這兩種基本雙曲函數推導而來，該函數將變量全部映射到(-1,1)區間。函數公式如下所示：

import numpy as np
import matplotlib.pyplot as plt

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

x = np.arange(-10,10,0.01)
y = sigmoid(x)
plt.plot(x,y,linewidth = 3,label = "tanh",color="r")
plt.grid()
plt.legend()
plt.show()