size=201;
ar=zeros(size,size);
ar((size+1)/2,(size+1)/2)=100;
figure('Position',[100,100,200,200])
ct=0;
for i=1:10000
 [i,ct]
 cth=1-2*rand;
 sth=sqrt(1-cth*cth);
 sth=sth*(1-2*(rand < .5));
 x=round((1+0.5*cth)*(size+1)/2);
 y=round((1+0.5*sth)*(size+1)/2);
 for j=1:10000
  xlast=x;
  ylast=y; 
  ch=rand;
  x=x+1*(ch < .25);
  x=x-1*((ch >= .25) & (ch < .5));
  y=y+1*((ch >= .5) & (ch < .75));
  y=y-1*(ch >= .75);
  if (x < 1 | y < 1 | x > size | y > size)
   break
  end
  if (ar(x,y) == 100)
   ar(xlast,ylast)=100;
   ct=ct+1;
   image(ar)
   shading flat
   colormap(waves)
   axis('square')
   drawnow
   break
  end
 end
end