User`s guide

LTI Properties
2-29
Most of these properties are dedicated to storing the model data. Note that the
matrix is set to
[] (the empty matrix) for standard state-space models, a
storage-efficie nt shorthand for the true value .
The
Variable property is only an attrib ute of TF and ZPK objects. This
property defines the frequency variable of transfer functions. The default
values are
's' (Laplace variable ) in continuous time and 'z' (Z-transform
variable ) in d iscrete time. Alternative choices include
'p' ( eq uiv al e n t to )
and
'q' or 'z^–1' for the reciprocal ofthe variable. The influence of
the variable choice is mostly limited to the display of TF or ZPK models. One
exception isthe specification ofdiscrete-time transferfunctionswith
tf (seetf
on page 11-224 for details).
Note that
tf producesthesameresultasfilt when the Variable property is
set to
'z^–1' or 'q'.
Finally, the
StateName propertyis analogoustotheInputName andOutputName
properties and keeps track of the state names in state-space models.
e
Descriptor matrix 2-D real matrix
StateName
State names Cell vector of strings
Table 2-8: FRD-Specific Properties
Property Name Description Property Value
Frequency
Frequency data points Real-valued vector
ResponseData
Frequency response Complex-valued
multidimensional array
Units
Units for frequency String 'rad/s' or 'Hz'
Table 2-7: SS-Specific Properties (Continued)
Property Name Description Property Value
E
E
EI
=
s
z
s
qz
1
–
=
z