% 彈簧振子 
close all 
T=0:40; 
y=mod(T,2)*2-1; 
y(1:3)=0;y(end-3:end)=0; 
hold on; 
set(gcf,'doublebuffer','on'); 
H1=plot(T,y); 
axis([0,70,-1,10]) 
tx=1.4*cos(2*pi*(0:.01:1)); 
ty=0.3*sin(2*pi*(0:.01:1)); 
plot([T(end),T(end)],[-1,3],'r:') 
X=T(end)+tx;Y=y(end)+ty; 
H2=fill(X,Y,'r');% ,'EraseMode','xor' 
k=1; 
t=0; 
xlabel('Please press "space" key and stop this program!',... 
   'fontsize',14,'color','r'); 
text(15,7,'Spring pendunlum','fontsize',18,'color','b') 
while k 
   s=get(gcf,'currentkey'); 
   if strcmp(s,'space'); 
       clc;k=0; 
   end 
   pause(0.04); 
   dt=1+0.5*cos(2*pi*t); 
   t=t+0.02; 
   Tk=T;Tk(4:end)=T(4:end)*dt; 
   set(H1,'xdata',Tk); 
   X=T(end)*dt+tx; 
   set(H2,'xdata',X); 
   set(H2,'facecolor',rand(1,3)); 
end 
figure(gcf);