User`s guide

Creating LTI Models
2-21
produces
Transfer function:
z – 0.2
-------
z + 0.3
Sampling time: unspecified
Note: Do no t simply omit Ts in this case . This would make h a
continuous-time transfer function.
Ifyouforgettospecifythesampletimewhencreatingyourmodel,youcanstill
set it to the correct value by reassigning the LTI property
Ts. See “Sample
Time” on page 2-34 for more information on setting this property.
Discrete-Time TF and ZPK Models
Youcanspecifydiscrete-timeTFandZPKmodelsusingtf andzpk as indicated
above. Alternatively, it is often convenient to specify such models by:
1 Defining the variable z as a particular discrete-time TF or ZPK model with
theappropriatesampletime
2 Entering your TF or ZPK model directly as a rational e xpression in z.
This approach parallels the procedure for specifying continuous-time TF or
ZPK models using rational expressions. This procedure is described in “SISO
Transfer Function Models” on page 2-8 and “SISO Zero-Pole-Gain Models” on
page 2-12.
For example,
z = tf('z', 0.1);
H = (z+2)/(z^2 + 0.6*z + 0.9);
creates the same TF model as
H = tf([1 2], [1 0.6 0.9], 0.1);