python中sigmoid函数是什么

import matplotlib.pyplot as plt

import numpy as np

def sigmoid(x):

    # 直接返回sigmoid函数

    return 1. / (1. + np.exp(-x))

def plot_sigmoid():

    # param:起点，终点，间距

    x = np.arange(-8, 8, 0.2)

    y = sigmoid(x)

    plt.plot(x, y)

    plt.show()

if __name__ == '__main__':

    plot_sigmoid()