clf,clear
a=0;b=4;c=0;d=4;n=15;
[X,Y]=meshgrid(linspace(a,b,n),linspace(c,d,n));
z=X.*Y;
Fx=cos(atan(X.*Y));Fy=sqrt(1-Fx.^2);
quiver(X,Y,Fx,Fy,0.5),hold on,axis([a,b,c,d])
%在每一網格點繪制相應的二維斜率矢量;0.5是控制矢量大小的控制參數,可以調整
[x,y]=ade45('zxy2_5f',[0,4],0.4);
plot(x,y,'r.-')