function diamond()
%實現點沿圓周運動的動畫
t=0:pi/2000:pi*2;
x=sin(t);
y=cos(t);
plot(y,x,'b');
axis equal
n=length(t);
h=line('color','g','linestyle','.',...
    'marker','.','markersize',50,'erasemode','xor');
i=1;
while i
    set(h,'xdata',y(i),'ydata',x(i));
    drawnow;
    i=i+1;
    if i>n 
        i=1;
    end
end