K=1;
tau1=1;
tau2=4;
xi=-1;
sis1=tf(K*[xi 1],conv([tau1 1],[tau2 1]));
sis2=tf(K*[4*xi 1],conv([tau1 1],[tau2 1]));
sis3=tf(K*[8*xi 1],conv([tau1 1],[tau2 1]));
step(sis1,sis2,sis3,30);
legend('\xi','4 \xi','8 \xi');

K=-1;
sis1=tf(K*[xi 1],conv([tau1 1],[tau2 1]));
sis2=tf(K*[4*xi 1],conv([tau1 1],[tau2 1]));
sis3=tf(K*[8*xi 1],conv([tau1 1],[tau2 1]));
figure; step(sis1,sis2,sis3,30);
legend('\xi','4 \xi','8 \xi');
