matlab bp神经网络的实现

%% I. 清空环境变量
clear all
clc

%% II. 训练集/测试集产生
%%
% 1. 导入数据
load spectra_data.mat

%%
% 2. 随机产生训练集和测试集
temp = randperm(size(NIR,1));
% 训练集——50个样本
P_train = NIR(temp(1:50),:)';
T_train = octane(temp(1:50),:)';
% 测试集——10个样本
P_test = NIR(temp(51:end),:)';
T_test = octane(temp(51:end),:)';
N = size(P_test,2);

%% III. 数据归一化
[p_train, ps_input] = mapminmax(P_train,0,1);
p_test = mapminmax('apply',P_test,ps_input);

[t_train, ps_output] = mapminmax(T_train,0,1);

%% IV. BP神经网络创建、训练及仿真测试
%%
% 1. 创建网络
net = newff(p_train,t_train,9);

%%
% 2. 设置训练参数
net.trainParam.epochs = 1000;
net.trainParam.goal = 1e-3;
net.trainParam.lr = 0.01;

%%
% 3. 训练网络
net = train(net,p_train,t_train);

%%
% 4. 仿真测试
t_sim = sim(net,p_test);

%%
% 5. 数据反归一化
T_sim = mapminmax('reverse',t_sim,ps_output);

%% V. 性能评价
%%
% 1. 相对误差error
error = abs(T_sim - T_test)./T_test;

%%
% 2. 决定系数R^2
R2 = (N * sum(T_sim .* T_test) - sum(T_sim) * sum(T_test))^2 / ((N * sum((T_sim).^2) - (sum(T_sim))^2) * (N * sum((T_test).^2) - (sum(T_test))^2)); 

%%
% 3. 结果对比
result = [T_test' T_sim' error']

%% VI. 绘图
figure
plot(1:N,T_test,'b:*',1:N,T_sim,'r-o')
legend('真实值','预测值')
xlabel('预测样本')
ylabel('辛烷值')
string = {'测试集辛烷值含量预测结果对比';['R^2=' num2str(R2)]};
title(string)