brownian

Brownian motion simulation:
USAGE: brownian(3) Simulate 3 particles.
 Using the EraseMode property is appropriate for long sequences 
 of simple plots where the change from frame to frame is minimal. 
 Here is an example showing simulated Brownian motion. 
 Specify a number of particles 
 and a temperature or velocity, such as

function brownian(NParticles )
%Brownian motion simulation:
%USAGE: brownian(3) Simulate 3 particles.
% Using the EraseMode property is appropriate for long sequences
% of simple plots where the change from frame to frame is minimal.
% Here is an example showing simulated Brownian motion.
% Specify a number of particles
% and a temperature or velocity, such as
s = .02
% The best values for these two parameters depend upon the speed
% of your particular computer.
% Generate particles random points with (x,y) coordinates
% between -1/2 and +1/2:
x = rand(NParticles,1)-0.5;
y = rand(NParticles,1)-0.5;

% Plot the points in a square with sides at -1 and +1.
% Save the handle for the vector of points and
% set its EraseMode to xor.
% This tells the MATLAB graphics system not to redraw
% the entire plot when the coordinates of one point are changed,
% but to restore the background color in the vicinity
% of the point using an exclusive or operation:
h = plot(x,y,'.');
axis([-1 1 -1 1])
axis square
grid off
set(h,'EraseMode','xor','MarkerSize',18)
% Now begin the animation. Here is an infinite while loop,
% which you can eventually exit by typing Ctrl+c.
% Each time through the loop, add a small amount of normally
% distributed random noise to the coordinates of the points.
% Then, instead of creating an entirely new plot,
% change the XData and YData properties of the original plot:
while 1
   drawnow
   pause(0.05)
   x = x + s*randn(NParticles,1);
   y = y + s*randn(NParticles,1);
   set(h,'XData',x,'YData',y)
end