Specifications

2 LTI Models
2-8
Creating LTI Models
The functions tf, zpk, ss,andfrd create transfer function models,
zero-pole-gain models, state-space models, and frequency response data
models,respectively.Thesefunctionstake themodeldataasinputandproduce
TF, ZPK, SS, or FRD objects that store this data in a single MATLAB variable.
This section shows how to create continuous or discrete, SISO or MIMO LTI
models with
tf, zpk, ss,andfrd.
Note You can only specify TF, ZPK, and SS models for systems whose
transfer matrices have real-valued coefficients.
Transfer Function Models
This section explains how to specify continuous-time SISO and MIMO transfer
function models. The specification of discrete-time transfer function models is
asimpleextensionofthecontinuous-timecase(see“Discrete-TimeModels”on
page 2-19). In this section you can also read about how to specify transfer
functions consisting of pure gains.
SISO Transfer Function Models
A continuous-time SISO transfer function
is characterized by its numerator and denominator , both
polynomials of the Laplace variable s.
There are two ways to specify SISO transfer functions:
•Using the
tf command
•As rational expressions in the Laplace variable s
To specify a SISO transfer function model using the
tf
command, type
h = tf(num,den)
hs
()
ns
()
ds
()
-----------
=
ns
()
ds
()
hs() ns()ds()⁄=