%?基于BP神經網絡對非線性函數進行逼近
tic
clear?all
close?all
%初始化部分

%初始化學習參數
eta=0.3;
%?初始化權值矩陣
wij=2*rand（25）-1;
wjk=2*rand（51）-1;
%?初始化閾值
thetaj=2*rand（51）-1;
thetak=2*rand（1）-1;
%設定誤差標準
errstd=0.05;
errall=10;

xteach1=0:0.2*pi:2*pi;
xteach2=0:0.2*pi:2*pi;
for?p=1:11
????for?q=1:11
??????????%yteach（pq）=0.2*（sin（xteach1（q））+cos（xteach2（p）））+0.5;
??????????yteach（pq）=?sin（xteach1（p））*cos（xteach2（q））;
????end
end


while?errall>=errstd??
????for?p=1:11
????????for?q=1:11
????????%取樣本
????????xt=[xteach1（p）;xteach2（q）];
????????yt=yteach（pq）;
????????
????????%計算各層的輸出，前向傳播
????????oi=xt;
????????netj=wij‘*xt;
????????oj=1./（1+exp（-（netj-thetaj）））;
????????netk=wjk‘*oj;
????????ok=1./（1+exp（-（netk-thetak）））;
????????y=ok;
????????
????????%計算各層誤差?后向傳播
????????deltak=（yt-y）.*ok.*（1-ok）;
????????deltaj=wj