switch flag error

I am trying to find out why is this an error if it came out from a book. The m-file should be saved as a function or script please see code:

function [sys,x0,str,ts] = s_anm81s(t,x,u,flag)
switch flag,
    case 0,
        [sys,x0,str,ts]=md1InitializeSizes;
    case 2,
        sys=md1Update(t,x,u);
    case 3,
        sys=md1Outputs(t,x,u);
    case 9,
        sys=md1Terminate(t,x,u);
    otherwise
        error(['Unhandled flag = ',num2str(flag)]);
end

function [sys,x0,str,ts]=md1InitializeSizes()
sizes = simsizes;
sizes.NumContStates=0;
sizes.NumDiscStates=0;
sizes.NumOutputs=0;
sizes.NumInputs=1;
sizes.DirFeedthrough=0;
sizes.NumSampleTimes=1;
sys=simsizes(sizes);
x0=[];
str=[];
ts=[0.25 0];
if(isempty(findobj('UserData',gcb)))
    h_fig=figure('Position', [200 200 400 300],...
    'MenuBar','none','NumberTitle','off',...
    'Resize', 'off',...
    'Name', ([gcs,'RollingDisk']));
    set(h_fig,'UserData',gcb);
    set(h_fig,'DoubleBuffer','on');
r=2;
R=12;
q=r;
thp=0:0.2:pi;
xp=R*cos(thp);
yp=-R*sin(thp);
xp=[xp,-R,-(R+q),-(R+q),(R+q),(R+q),R];
yp=[yp,0,0,-(R+q),-(R+q),0,0];
cl_x=[0,0];
cl_y=[0,-R];
thp=0:0.3:2.3*pi;
xd=r*cos(thp);
yd=r*sin(thp);
hd=fill(xp,yp,[0.85,0.85,0.85]);
hold on;
set(hd,'EraseMode','none');
axis('equal');axis('off');
hd0=plot(cl_x,cl_y,'k--');
set(hd0,'EraseMode','none');
theta=0;
xc=(R-r)*sin(theta);
yc=-(R-r)*cos(theta);
psi=theta*(R-r)/r;
xm_c=r*sin(psi);
ym_c=r*cos(psi);
xm=xc+xm_c;
ym=yc+ym_c;
hd2=fill(xd+xc,yd+yc,[0.85,0.85,0.85]);
hd3=plot([xc,xm],[yc,ym],'k');
set_param(gcb,'UserData',[hd2,hd3]);
end

function sys=md1Update(t,x,u)
sys=[];
r=2;
R=12;
q=r;
userdat=get_param(gcb,'UserData');
hd2=userdat(1);
hd3=userdat(2);
theta=u(1);
xc=(R-r)*sin(theta);
yc=-(R-r)*cos(theta);
psi=theta*(R-r)/r;
    xm_c=r*sin(psi);
    ym_c=r*cos(psi);
    xm=xc+xm_c;
    ym=yc+ym_c;
    thp=0:0.3:2*pi;
    xd=r*cos(thp);
    yd=r*sin(thp);
    set(hd2,'XData',xd+xc);
    set(hd2,'YData',yd+yc);
    set(hd3,'XData',[xc, xm]);
    set(hd3,'YData',[yc,ym]);

function sys=md1Outputs(t,x,u)
    sys=[];

function sys=md1Terminate(t,x,u)
      sys=[];

[EDITED, 12-Dec-2011 14:01 UTC, Jan Simon]: Code formatted

[the cyclist]

This would be astronomically easier to read if you used the "Code" button to format your post.

[Walter Roberson]

http://www.mathworks.com/matlabcentral/answers/13205-tutorial-how-to-format-your-question-with-markup

[Jan]

Dear Gabriel: I've formatted the code for you this time. If you do not care about a proper formatting and the comments, the readers get the impression, that you do not really care about the question and do not really need an answer.

[Jan]

Which error do you get - please copy the complete message? How do you call this funtion?

[muhammad ghufran]

@Jan I am facing same issue like error come "Switch flag" how can I solve this error please guide me