If you assign outputs to lsim, you don't get the specialized plot and simply get the output variables. So, if you add an extra line to your code as follows, you're good to go:
H = [tf([2 5 1],[1 2 3])];
[u,t] = gensig('square',4,10,0.1);
[yout,tout]= lsim(H,u,t);
plot(tout,yout)
- Sebastian
