z domain root locus

z = tf('z');
sys = (0.0173*z)/((z - 0.9048)*(z - 0.8187));
rlocus(sys)
axis([-1 1 -1 1])
zeta = 0.5;
Wn = 0.2;
zgrid(zeta,Wn)

 http://ctms.engin.umich.edu/CTMS/index.php?aux=Extras_Dsserror