s domain transfer function to z domain

functions that are frequently used:
1.tf
2.poly & roots
3.c2d
4.zpk

Example:
>> sys=tf(0.1, poly([0 -0.1]))

Transfer function:
0.1
-----------
s^2 + 0.1 s

>> zsys=c2d(sys,1,'zoh')

Transfer function:
0.04837 z + 0.04679
----------------------
z^2 - 1.905 z + 0.9048

Sampling time: 1
>> zsys_zpk=zpk(zsys)

Zero/pole/gain:
0.048374 (z+0.9672)
-------------------
(z-1) (z-0.9048)

Sampling time: 1