Z=[]; K=10; P=[-1;-2;-3;-4]; G=zpk(Z,P,K); 
G1=tf(G); [R,PP,X]=residue(G1.num{1},[G1.den{1},0])

[y,t]=step(G); 
for i=1:5, y=[y, R(i)*exp(PP(i)*t)]; end
plot(t,y)

plot(t,y(:,1),'-',t,sum(y(:,4:6)')',':');

Z=[]; K=10; P=[-1;-2;-9;-10]; G=zpk(Z,P,K); 
G1=tf(G); [R,PP,X]=residue(G1.num{1},[G1.den{1},0]);
[y,t]=step(G); 
for i=1:5, y=[y, R(i)*exp(PP(i)*t)]; end
plot(t,y), figure
plot(t,y(:,1),'-',t,sum(y(:,4:6)')',':');