Specifications

2 LTI Models
2-22
clashes with the “descending powers of ”conventionassumedbytf (see
“Transfer Function Models” on page 2-8, or
tf). For example,
h = tf([1 0.5],[1 2 3])
produces the transfer function
which differs from by a factor .
Toavoidsuchconventionclashes, theControlSystem Toolboxoffersaseparate
function
filt dedicated to the DSP-like specification of transfer functions. Its
syntax is
h = filt(num,den)
for discrete transfer functions with unspecified sample time, and
h = filt(num,den,Ts)
to further specify the sample time Ts. This function creates TF objects just like
tf,butexpectsnum and den to list the numerator and denominator coefficients
in ascending powers of . For example, typing
h = filt([1 0.5],[1 2 3])
produces
Transfer function:
1 + 0.5 z^–1
-------------------
1 + 2 z^–1 + 3 z^–2
Sampling time: unspecified
You can also use filt tospecifyMIMO transfer functionsin . Just as for tf,
the input arguments
num and den are then cell arrays of row vectors of
appropriate dimensions (see “Transfer Function Models” on page 2-8 for
details). Note that each row vector should comply with the “ascending powers
of ” convention.
z
z 0.5+
z
2
2z 3++
----------------------------
Hz
1–
()
z
z
1–
z
1–
z
1–