学步园

自创建神经网络， 使用传递函数（激活函数）为logsig（S型对数函数）。具体实现如下：

%自创建神经网络<br /> P=[-3,2];<br /> T=[0.4,0.8];<br /> Wrange=-4:0.4:4;<br /> Brange=-4:0.4:4; %W值的行向量、B值的行向量<br /> ES=errsurf(P,T,Wrange,Brange,'logsig'); %求单神经元的误差平面（只用在单神经元中）<br /> %Error surface of single input neuron<br /> % errsurf(P,T,WV,BV,F) takes these arguments,<br /> % P -- 1 x Q matrix of input vectors<br /> % T -- 1 x Q matrix of target vectors<br /> % WV -- Row vector of values of W<br /> % BV -- Row vector of values of B<br /> % F -- Transfer function (string)<br /> % and returns a matrix of error values over WV and BV.<br /> mesh(ES,[60,30]); %作三维网状面，视角【60，30】<br /> title('Error Surface Graph') %标题<br /> xlabel('W')<br /> ylabel('B')<br /> zlabel('Sum Squared Error')<br /> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%华丽分割线<br /> max_epoch=1500; %赋最大训练次数<br /> err=[];<br /> xx=[];<br /> yy=[]; %定义矩阵<br /> lr=0.5;<br /> W1=-4*rand(1); %赋权值和偏差的初值<br /> b1=-4*rand(1);<br /> x1=W1;<br /> y1=b1;<br /> for i=1:max_epoch<br /> A1 = logsig(W1*P+b1*ones(1,2)); %计算输出<br /> % Log sigmoid transfer function<br /> %<br /> % logsig is a transfer function. Transfer functions calculate a layer's output from its net input.<br /> % logsig(N) takes one input,<br /> % N -- S x Q matrix of net input (column) vectors<br /> % and returns each element of N squashed between 0 and 1.<br /> % logsig(code) returns useful information for each code string:<br /> % 'deriv' -- Name of derivative function<br /> % 'name' -- Full name<br /> % 'output' -- Output range<br /> % 'active' -- Active input range<br /> E = T-A1; %求误差<br /> D1 = A1.*(1-A1).*E; %矩阵对应元素相乘<br /> dW1 = D1*P'*lr; %求权值增量<br /> db1 = D1*ones(2,1)*lr; %求偏差增量<br /> newx = W1(1,1) + dW1(1,1); %新的权值<br /> W1(1,1) = newx;<br /> xx =[xx newx];<br /> newy = b1(1) + db1(1); %新的偏差<br /> b1(1) = newy;<br /> yy =[yy newy];<br /> SSE = sumsqr(E); %求误差平方和<br /> err=[err SSE];<br /> if (SSE<1e-8)<br /> break;<br /> end<br /> end </p> <p>figure(2)<br /> [C,h] =contour(Wrange,Brange,ES); %作等高线图，ES为高<br /> %返回等高线矩阵C，列向量h是线或对象的句柄，一条线一个句柄，这些被用作CLABEL的输入，<br /> %每个对象包含每个等高线的高度<br /> %A contour graph displays isolines of matrix Z. Label the contour lines using clabel<br /> % contour(X,Y,Z,n), and contour(X,Y,Z,v) draw contour plots of Z.<br /> % X and Y specify the x- and y-axis limits. When X and Y are matrices,<br /> %they must be the same size as Z, in which case they specify a surface,<br /> %as defined by the surf function.<br /> % If X or Y is irregularly spaced,<br /> % contour calculates contours using a regularly spaced contour grid,<br /> % then transforms the data to X or Y.<br /> clabel(C,h) %标上高度值<br /> colormap cool %背景的颜色cool<br /> axis('equal')<br /> hold on<br /> plot(x1,y1,'r+')<br /> plot(xx,yy,'b*') %作矩阵变化曲线<br /> hold off </p> <p>figure(3)<br /> plot(err) %作误差曲线<br /> err<br />