例6-13.m

这是一个MATLAB7.0基础与提高例题的所有源码

clf,a=-2;b=4;
xmin=a;xmax=b;ymin=a;ymax=b;  %设置变量范围和坐标轴显示范围
x1=linspace(xmin,xmax,100);x2=linspace(ymin,ymax,100);
[X1,X2]=meshgrid(x1,x2);
[Z,DZ1,DZ2]=jt(X1,X2);
axis([xmin xmax ymin ymax]),hold on,
axis equal,
plot([1.46808510638298],[1.148936170212776],'o'),
axis([xmin xmax ymin ymax]),hold on,
x=[ ];y=[ ];
disp('Select a point by put on mouse left_key')
disp('Stop selecting point by put on mouse right_key')
button=1;
x=[ ];y=[ ];
while button==1
    [xi,yi,button]=ginput(1);
    plot([xi],[yi],'r.','MarkerSize',10),hold on,
    [zi,dz1,dz2]=jt(xi,yi);
    v=zi;
    contour(X1,X2,Z,[v v],'-'),
    axis([xmin xmax ymin ymax]),
    x=[x,xi];y=[y,yi];
    H_line2=plot(x,y);
    set(H_line2,'color','red','linewidth',2);
    xt=xi-dz1;yt=yi-dz2;
    H_line=plot([xi xt],[yi yt],'k:','linewidth',1);
End

其中使用的函数 的代码如下：
function [f,df1,df2]=jt(x,x2)
f=8*x.*x+9*x2.*x2-10*x.*x2-12*x-6*x2;
if nargout>1
    df1=2*8*x-10*x2-12*ones(size(x));
    df2=2*8*x2-10*x-12*ones(size(x2));
end