% BROWNIAN   Two-dimensional random walk.%   What is the expansion rate of the cloud of particles?shgclfset(gcf,'doublebuffer','on')delta = .002;x = zeros(100,2);h = plot(x(:,1),x(:,2),'.');axis([-1 1 -1 1])axis squarestop = uicontrol('style','toggle','string','stop');while get(stop,'value') == 0   x = x + delta*randn(size(x));   set(h,'xdata',x(:,1),'ydata',x(:,2))   drawnowendset(stop,'string','close','value',0,'callback','close(gcf)')