n = (-20:20);
u_n = n>=0;
u_n_2 = n>=2;
u_n_5 = n>=5;
u_diff = u_n_2 - u_n_5;
subplot(3,1,1); stem(n,u_n_2);xlim([-15 15]); ylim([-2 2])
subplot(3,1,2); stem(n,u_n_5);xlim([-15 15]); ylim([-2 2])
subplot(3,1,3); stem(n,u_diff);xlim([-15 15]); ylim([-2 2])
