function Xprime = SI(t,X)
mu = .001;
beta = 2;
lambda = 0.001;
gamma = 1/5;
% mu = 0.003;
% beta = 0.02;
% lambda = 0.25;
% gamma = 0.1;
% mu = 0.003;
% beta = 0.07;
% lambda = 0.25;
% gamma = 0.2;

Xprime = zeros (3,1);
N=10001;
Xprime(1)=lambda - beta*X(1)*X(2)/N-mu*X(1);
Xprime(2)=beta*X(1)*X(2)/N-(gamma + mu)*X(2);
Xprime(3)=gamma*X(2)-mu*X(3);
% Sprime=lambda - beta*S*I-mu*S;
% Iprime=beta*S*I-(gamma + mu)*I;