Input and output of transfer function in matlab

A transfer function of a system, sub-system, or component is a mathematical function that models the system's output for each possible input

M=2;
b=14;
q=20;
num=[1];
G=tf(num,[M b q]);
syms t
F = 2*(heaviside(t)-heaviside(t-2));
T = linspace(0, 3);
sympref('HeavisideAtOrigin', 0);
u = double(subs(F, t, T));
y1 = lsim(G, u, T);
sympref('HeavisideAtOrigin', 1);
u = double(subs(F, t, T));
y2 = lsim(G, u, T);

syms s
y3 = ilaplace(1/(M*s^2 + b*s + q)*(2/s - 2*exp(-2*s)/s),s,t);
y3 = double(subs(y3,t,T)).';
plot(T,y1,T,y2,T,y3,'o')
legend('HeavisdeOrigin = 0','HeavisdeOrigin = 1','exact','Location','South')