global alpha beta0 beta1 gamma mu

mu = 0.02;
alpha = 35.84;
gamma = 100;
beta0 = 1800;
beta1 = 0.2;

options = odeset('MaxStep',0.01);
[T,Y] = ode45('func_SEIR',[0 50],[0.0658 0.0007 0.0002 0],options);  

figure(1)
plot(T,-log(Y(:,3)));
xlabel('t');
ylabel('-ln(I)');

figure(2);
plot(-log(Y(:,1)),-log(Y(:,3)));
xlabel('-ln(S)');
ylabel('-ln(I)');
