function A = CRR(N, d,u,p,a)
% CRR gives a sample path of a CRR stock price model 
if nargin < 5
    a=1;
end
if nargin < 4 
   p=0.5;
end
if nargin ==1
    d = 0.9;
    u = 1.15;
end 
Y(1) = a;
for i = 2:N
    x = rand; 
    if x < p
        r = d;
    else
        r=u;
    end
    Y(i) = r * Y(i-1);
    end
A=Y;