# -*- coding: utf-8 -*-
"""
Created on Wed Mar 16 23:46:31 2022
@author: liaoy
"""
import numpy as np
import matplotlib.pyplot as plt
import pandas as pd
def sigmoid(x):
"""
隐含层和输出层对应的函数法则
"""
return 1/(1+np.exp(-x))
def BP(data_tr, data_te, maxiter=3000):
# --pandas是基于numpy设计的,效率略低
# 为提高处理效率,转换为数组
data_tr, data_te = np.array(data_tr), np.array(data_te)
# --隐层输入
# -1: 代表的是隐层的阈值
net_in = np.array([0.0, 0, -1])
w_mid = np.random.rand(3, 4) # 隐层权值阈值(-1x其中一个值:阈值)
# 输出层输入
# -1:代表输出层阈值
out_in = np.array([0.0, 0, 0, 0, -1])
w_out = np.random.rand(5) # 输出层权值阈值(-1x其中一个值:阈值)
delta_w_out = np.zeros([5]) # 存放输出层权值阈值的逆向计算误差
delta_w_mid = np.zeros([3, 4]) # 存放因此能权值阈值的逆向计算误差
yita = 1.75 # η: 学习速率
Err = np.zeros([maxiter]) # 记录总体样本每迭代一次的错误率
# 1.样本总体训练的次数
for it in range(maxiter):
# 衡量每一个样本的误差
err = np.zeros([len(data_tr)])
# 2.训练集训练一遍
for j in range(len(data_tr)):
net_in[:2] = data_tr[j, :2] # 存储当前对象前两个属性值
real = data_tr[j, 2]
# 3.当前对象进行训练
for i in range(4):
out_in[i] = sigmoid(sum(net_in*w_mid[:, i])) # 计算输出层输入
res = sigmoid(sum(out_in * w_out)) # 获得训练结果
err[j] = abs(real - res)
# --先调节输出层的权值与阈值
delta_w_out = yita*res*(1-res)*(real-res)*out_in # 权值调整
delta_w_out[4] = -yita*res*(1-res)*(real-res) # 阈值调整
w_out = w_out + delta_w_out
# --隐层权值和阈值的调节
for i in range(4):
# 权值调整
delta_w_mid[:, i] = yita * out_in[i] * (1 - out_in[i]) * w_out[i] * res * (1 - res) * (real - res) * net_in
# 阈值调整
delta_w_mid[2, i] = -yita * out_in[i] * (1 - out_in[i]) * w_out[i] * res * (1 - res) * (real - res)
w_mid = w_mid + delta_w_mid
Err[it] = err.mean()
plt.plot(Err)
plt.show()
# 存储预测误差
err_te = np.zeros([100])
# 预测样本100个
for j in range(100):
net_in[:2] = data_te[j, :2] # 存储数据
real = data_te[j, 2] # 真实结果
# net_in和w_mid的相乘过程
for i in range(4):
# 输入层到隐层的传输过程
out_in[i] = sigmoid(sum(net_in*w_mid[:, i]))
res = sigmoid(sum(out_in*w_out)) # 网络预测结果输出
err_te[j] = abs(real-res) # 预测误差
print('rest:', rest, ' real:', real)
plt.plot(err_te)
plt.show()
if "__main__" == __name__:
# 1.读取样本
data_tr = pd.read_csv("D:\\spyder\\12.CUI\\3.3 data_te(1).txt")
data_te = pd.read_csv("D:\\spyder\\12.CUI\\3.3 data_tr(1).txt")
BP(data_tr, data_te, maxiter=3000)
如上为BP神经网络代码,先定义sigmoid和他的导数。后代码如上图所示,我设置的代码运行次数为3000次,运算的过程如下图,但只有运行到100的图像
该数据和代码还有优化空间。