function [sys,x0]=crtanim2(t,x,u,flag,ts);
%CRTANIM2 S-function for animating the motion of a mass-spring system.

%   Ned Gulley, 6-21-93
%   Copyright 1990-2002 The MathWorks, Inc.
%   $Revision: 5.9 $

global xSpr2 xBx12 xBx22 dblcart1

offset=4;

if flag==2,

  if any(get(0,'Children')==dblcart1),
    if strcmp(get(dblcart1,'Name'),'dblcart1 Animation'),
      set(0,'currentfigure',dblcart1)
      u(2)=u(2)+offset;
      distance=u(2)-u(1);
      hndl=get(gca,'UserData');
      x=[xBx12+u(1); xSpr2/4*distance+u(1); xBx22+distance+u(1)];
      set(hndl,'XData',x);
      drawnow;
    end
  end
  sys=[];

elseif flag == 4 % Return next sample hit
  
  % ns stores the number of samples
  ns = t/ts;

  % This is the time of the next sample hit.
  sys = (1 + floor(ns + 1e-13*(1+ns)))*ts;

elseif flag==0,

  % Initialize the figure for use with this simulation
  animinit('dblcart1 Animation');
  dblcart1 = findobj('Type','figure','Name','dblcart1 Animation');
  axis([-10 20 -7 7]);
  hold on;

  xySpr2=[ ...
        0.0       0.0
        0.4       0.0
        0.8       0.65
        1.6      -0.65
        2.4       0.65
        3.2      -0.65
        3.6       0.0
        4.0       0.0];
  xyBx12=[ ...
        0.0       1.1
        0.0      -1.1
       -2.0      -1.1
       -2.0       1.1
        0.0       1.1];
  xyBx22=[ ...
        0.0       1.1
        2.0       1.1
        2.0      -1.1
        0.0      -1.1
        0.0       1.1];
  xBx12=xyBx12(:,1);
  yBx12=xyBx12(:,2);
  xBx22=xyBx22(:,1);
  yBx22=xyBx22(:,2);
  xSpr2=xySpr2(:,1);
  ySpr2=xySpr2(:,2);

  x=[xBx12; xSpr2; xBx22(:,1)+offset];
  y=[yBx12; ySpr2; yBx22];

  % Draw the floor under the sliding masses
  plot([-10 20],[-1.3 -1.3],'yellow', ...
       [-10:19;-9:20],[-2 -1.3],'yellow','LineWidth',2);
  hndl=plot(x,y,'y','EraseMode','background','LineWidth',3);
  set(gca,'UserData',hndl);

  sys=[0 0 0 2 0 0];
  x0=[];

end;