x1=0.5;
y1=0.9;
x2=0.1;
y2=0.1;
x3=0.9;
y3=0.1;
x=rand(1);
y=rand(1);
d=floor(1+3*rand(1));
if (d==1) 
   xp=(x+x1)/2;
   yp=(y+y1)/2;
elseif (d==2) 
   xp=(x+x2)/2;
   yp=(y+y2)/2;
else
   xp=(x+x3)/2;
   yp=(y+y3)/2;
end
axis([0 1 0 1])
hold on
p=plot(xp,yp,'EraseMode','none','Color','red')
while 1
x=xp;
y=yp;
d=floor(1+3*rand(1));
if (d==1) 
   xp=(x+x1)/2;
   yp=(y+y1)/2;
elseif (d==2) 
   xp=(x+x2)/2;
   yp=(y+y2)/2;
else
   xp=(x+x3)/2;
   yp=(y+y3)/2;
end
set(p,'XData',xp,'YData',yp)
drawnow
end