b = [1 2];
a = [1 4 3 0];
[z,p,k]=tf2zp(b,a)
plot(real(z),imag(z),'o',real(p),imag(p),'x');
grid
axis([-4 4 -4 4])
xlabel('Real Part');
ylabel('Imaginary Part');
print -depsc2 zp_plot.eps

[r,p,k] = residue(b,a)