User`s guide

2 LTI Models
2-8
Creating LTI Models
The functions tf, zpk, ss,andfrd creat e transfer function models,
zero-pole-gain models, state-space models, and frequency response dat a
models,respectively.Thesefunctionst ake themodeldataas inputandproduce
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 re al -val ued coefficients.
Transfer Function Models
This sectio n explains ho w to spec if y continuous-time SISO and MIMO trans fer
function models. T he specification of discrete-time transfer function models i s
asimpleextensionofthecontinuous-timecase(see“Discrete-TimeModels”on
page 2-2 0) . In this s ect io n you can also read about how t o specify transfer
functions consisting of pure gains.
SISO Transfer Function Models
A continuous-time SISO transfer function
is cha racterized by its numerator and denominator , both
polynom ials of the Laplace variable s.
There are two ways to specify SISO transfer functions:
• Using the
tf command
• As rational expressio ns in t he Laplace variable s
To spe c ify a S I SO transfe r function model usin g the
tf
command, type
h = tf(num,den)
hs()
ns
()
ds()
-----------=
ns
()
ds
()
hs
()
ns
()
ds
()⁄=