% random walk with error  bars
% A. Sun 2/2005

clear; 
clf;

pts = 1000;
traj = 10;

% overlay error bars of width 3 sigma
i=0:100:pts;
xaxis=zeros(size(i));
e=(3/2)*sqrt(i);
errorbar(i,xaxis,e);
hold on;



% make ensemble of random walks

for t = 1:traj,
    
rwalk = [];
rw = 0;

if t == 1
    seed=1;
else 
    seed = rand_vec(pts);
end
rand_cust;  % make vector of random numbers


for i = 1:pts,
  if rand_vec(i) < 0.5
      rw=rw+1;
  else
      rw=rw-1;
  end
  rwalk = [rwalk rw];
end

plot(rwalk, 'r'); 

end