clc
clear
%定義要逼近的非線性函數(shù)
u=[-0.5:0.01:0.5];
t=exp(-1.9*(u+0.5))*sin(10*u);
figure;
plot(u,t,'r')
title('要逼近的非線性函數(shù)');
xlabel('時(shí)間');
ylabel('非線性函數(shù)');
%建立相應(yīng)的前饋BP網(wǎng)絡(luò)
net=newff([-0.5 0.5],[20,1],{'logsig' 'purelin'},'trainelm');
%對(duì)沒有訓(xùn)練的網(wǎng)絡(luò)進(jìn)行仿真
y1=sim(net,u); 
figure;
plot(u,t,'r',u,y1,'k')
title('沒有訓(xùn)練的網(wǎng)絡(luò)仿真結(jié)果');
xlabel('時(shí)間');
ylabel('仿真輸出（黑）  原函數(shù)（紅）');
%訓(xùn)練網(wǎng)絡(luò)
net.trainParam.epochs=50;
net.trainParam.goal=0.005;
[net,tr]=train(net,u,t);
plotperf(tr,net.trainParam.goal)   %BP網(wǎng)絡(luò)訓(xùn)練軌跡
y2=sim(net,u);
%繪出訓(xùn)練后的仿真結(jié)果
figure;
plot(u,t,'r',u,y1,'k',u,y2,'b')
title('訓(xùn)練后的網(wǎng)絡(luò)仿真結(jié)果');
xlabel('時(shí)間');
ylabel('仿真輸出');