% Added pauses to inforce uniform frame rate.  27 Oct 09 JMH.
 duration = 10;
 samp_per_sec = 20;
 x = pendulum(duration,samp_per_sec);

 t = 0:1/samp_per_sec:duration;
 l = .25;
 n = 3;

 figure(1), clf                
 set(gcf,'doublebuffer','on')  % keep figure from flashing in older MATLABs
 for k=1:n
    fill([-.5 .5 .5 -.5],[0 0 -.5*l -.5*l],.5*[1 1 1]); hold on
    plot([0 0], l*[0 4],'-','color',.7*[1 1 1])
    set(gca,'YDir','Reverse')
    axis equal, axis([-.5 .5 -.099 1]) 
 end
 xlabel(sprintf('t = %f',0))
 for j=1:length(t)
    tic;
    q = x(j,:)';                                               % horizontal displacements
        if j>1, delete(plt1(k)), delete(plt2(k)), end              % delete old chain
        plt1(k) = plot([q;0],(n:-1:0)*l,'k-','linewidth',1); hold on  % draw new one (black line)
        plt2(k) = plot(q, (n:-1:1)*l,'b.','markersize',40);         % draw new one (blue masses)
    xlabel(sprintf('t = %f',t(j)))
    set(gca,'YDir','Reverse')
    axis equal, axis([-.5 .5 -.099 1]) 
    drawnow
    if j==1, input('hit return to start'), end
    drawtime = toc;
    if (drawtime) < 1/samp_per_sec	% kill time 
	    pause(1/samp_per_sec - drawtime)
    end
 end