激活函数sigmoid和tanh

1.sigmoid函数也称为S型函数，该函数将变量全部映射到(0,1)区间。函数表达式如下所示：

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函数称为双曲正切函数，由双曲正弦和双曲余弦这两种基本双曲函数推导而来，该函数将变量全部映射到(-1,1)区间。函数公式如下所示：

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()