function sir = sir(t,x)
N = 1000;
beta = 0.25;
gamma = 0.1;
sir = zeros(2,1);
sir(1) = - beta * (x(1) / N) * x(2); %dS/dt
sir(2) = beta * (x(1) / N) * x(2) - gamma * x(2); %dI/dt


