clear all; close all;

alpha = 0.0011;
beta = 0.03;
gamma = 0.0013;

s(1) = 999
i(1) = 1
r(1) = 0
d(1) = 0

for t = 1:100
    s(t+1) = s(t) + (-alpha * i(t) * s(t))
    i(t+1) = i(t) + alpha*i(t)*s(t) - beta*i(t) - gamma * i(t)
    r(t+1) = r(t) + beta * i(t)
    d(t+1) = d(t) + gamma * i(t)
end

t = 1:101;
plot(t, s, t, i, t, r, t, d)
legend('Susceptible', 'Infected', 'Recovered', 'Dead')
grid on;
axis tight
xlabel('aika')
ylabel('ihmisten määrä')