clear all;

walk=zeros(100,100);
for j=1:100,
 finished=0;
 x0=50;
 y0=50;
 count=1;
 while (finished==0),
   walk(x0,y0)=walk(x0,y0)+1;
   a=rand(1.0);
   if (a<0.75),
      if (a<0.5),
         if (a<0.25),
            x0=x0+1;
         else
            x0=x0-1;
         end;
      else
         y0=y0+1;
      end;
   else
      y0=y0-1;
   end;
   if (walk(x0,y0)==0),
      walk(x0,y0)=1;
      x0=50;
      y0=50;
      count=count+1;
      if count>200,
         finished=1;
      end;   
   end;
 end;   
 x1=[1:1:100];
 y1=[1:1:100];
 v=[1:walk(50,50)/20.0:walk(50,50)];
 contour (x1,y1,walk,v);
 axis equal;
 disp('paused');
 pause;
end;