K=1;
tau=1;
sis1=tf(K,[tau 1]);
sis2=tf(K,[2*tau 1]);
sis3=tf(K,[4*tau 1]);
sis4=tf(K,[8*tau 1]);
step(sis1,sis2,sis3,sis4);
legend('\tau','2 \tau','4 \tau','8 \tau');

sis5=tf(2*K,[tau 1]);
figure; step(sis1,sis5);
legend('K','2 K');
