# -*- coding:utf-8 -*-
from matplotlib import pyplot as plt
import numpy as np
import mpl_toolkits.axisartist as axisartist


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


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


def relu(x):
    return np.where(x<0,0,x)


def prelu(x):
    return np.where(x<0,0.5*x,x)

def plot_sigmoid():
    x = np.arange(-10, 10, 0.1)
    y = sigmoid(x)
    fig = plt.figure()
    # ax = fig.add_subplot(111)
    ax = axisartist.Subplot(fig,111)
    ax.spines['top'].set_color('none')
    ax.spines['right'].set_color('none')
    # ax.spines['bottom'].set_color('none')
    # ax.spines['left'].set_color('none')
    ax.axis['bottom'].set_axisline_style("-|>",size=1.5)
    ax.spines['left'].set_position(('data', 0))
    ax.plot(x, y)
    plt.xlim([-10.05, 10.05])
    plt.ylim([-0.02, 1.02])
    plt.tight_layout()
    plt.savefig("sigmoid.png")
    plt.show()


def plot_tanh():
    x = np.arange(-10, 10, 0.1)
    y = tanh(x)
    fig = plt.figure()
    ax = fig.add_subplot(111)
    ax.spines['top'].set_color('none')
    ax.spines['right'].set_color('none')
    # ax.spines['bottom'].set_color('none')
    # ax.spines['left'].set_color('none')
    ax.spines['left'].set_position(('data', 0))
    ax.spines['bottom'].set_position(('data', 0))
    ax.plot(x, y)
    plt.xlim([-10.05, 10.05])
    plt.ylim([-1.02, 1.02])
    ax.set_yticks([-1.0, -0.5, 0.5, 1.0])
    ax.set_xticks([-10, -5, 5, 10])
    plt.tight_layout()
    plt.savefig("tanh.png")
    plt.show()


def plot_relu():
    x = np.arange(-10, 10, 0.1)
    y = relu(x)
    fig = plt.figure()
    ax = fig.add_subplot(111)
    ax.spines['top'].set_color('none')
    ax.spines['right'].set_color('none')
    # ax.spines['bottom'].set_color('none')
    # ax.spines['left'].set_color('none')
    ax.spines['left'].set_position(('data', 0))
    ax.plot(x, y)
    plt.xlim([-10.05, 10.05])
    plt.ylim([0, 10.02])
    ax.set_yticks([2, 4, 6, 8, 10])
    plt.tight_layout()
    plt.savefig("relu.png")
    plt.show()


def plot_prelu():
    x = np.arange(-10, 10, 0.1)
    y = prelu(x)
    fig = plt.figure()
    ax = fig.add_subplot(111)
    ax.spines['top'].set_color('none')
    ax.spines['right'].set_color('none')
    # ax.spines['bottom'].set_color('none')
    # ax.spines['left'].set_color('none')
    ax.spines['left'].set_position(('data', 0))
    ax.spines['bottom'].set_position(('data', 0))
    ax.plot(x, y)
    plt.xticks([])
    plt.yticks([])
    plt.tight_layout()
    plt.savefig("prelu.png")
    plt.show()


if __name__ == "__main__":
    plot_sigmoid()
    plot_tanh()
    plot_relu()
    plot_prelu()
 

效果：

                                                                            sigmoid函式

                                                                              tanh函式

                                                                               RELU函式

                                                                                  PRELU函式