For a SISO system, ‘t’ needs to be a vector:
t = linspace(0,10);
the full code being:
A = [0 1 0 0; 0 0 1 0; 0 0 0 1; -2 -5 -7 -2];
B = [0; 0; 0; 1];
C = [1 3 0 0];
D = 0;
t = linspace(0,10);
sys = ss(A,B,C,D);
x0 = [1 1 1 1];
u = exp(-0.3*t).*sin(2*pi*t);
lsim(sys, u, t)
grid
Create ‘t’ to be whatever you want.