User`s guide

Hard-Disk Read/Write Head Controller
9-23
To analyze the discrete system, plot its step response, type
step(Hd)
The system oscillates quite a bit. This is probably due to very light damping.
You can check this by computing the open-loop poles. Type
% Open–loop poles of discrete model
damp(Hd)
Eigenvalue Magnitude Equiv. Damping Equiv. Freq.
9.87e–01 + 1.57e–01i 9.99e–01 6.32e–03 3.16e+01
9.87e–01 – 1.57e–01i 9.99e–01 6.32e–03 3.16e+01
The poles have very light e quivalent damping and are near the unit circle. You
need to design a compensator that increases the damping of these poles.