%  MATLAB commands used to generate square wave movie

tmax=45;
nt=200;
nx=200;

% initialize vector and axes used for plotting
dt=tmax/(nt-1);
x=linspace(-10,10,nx);
y=zeros(1,nx);
for ix=1:nx
    y(ix)=f(x(ix));
end;
plot(x,y)
axis([-10 10 -1.5 1.5]);
lim=axis;
set(gca,'Position',[0.13    0.11    0.5    0.6]);
M=moviein(nt);

% loop to produce frames of the movie (nt frames total)
for it=1:nt
   t=dt*(it-1);
   for ix=1:nx
       s=x(ix)-t;
       r=x(ix)+t;
       F=f(s)-f(s+20)+f(s+40);
       G=f(r)-f(r-20)+f(r-40);
       y(ix)=0.5*(F+G);
   end;
   plot(x,y)
   axis(lim)
   drawnow;
   M(:,it)=getframe;
end;

% create Quicktime file containing movie
map=colormap;
qtwrite(M,map,'square wave movie',[12,3,3]);


%  m-file used to define IC function
function z=f(s)
if s>1
   z=0;
elseif s<-1
   z=0;
else
   z=1;
end;