User`s guide

3 Operations on LTI Models
3-8
I/O channel or g roup names) as a keyword. There are two ways you can specify
FRD models using frequencies:
• Using integers to index into the frequency vector of the FRD model
• Usinga Boolean(logical)expressiontospecifydesired frequencypoints inan
FRD model
For example, if
sys is an FRD model with five frequencies, (e.g.,
sys.Frequency=[1 1.1 1.2 1.3 1.4]), then you can create a new FRD model
sys2 by indexing into the frequencies of sys as follows.
sys2 = sys('frequency', 2:3);
sys2.Frequency
ans =
1.1000
1.2000
displays the second and third entries in the frequency v ector.
Similarly, you can use logical indexing into the frequencies.
sys2 = sys('frequency',sys.Frequency >1.0 & sys.Frequency <1.15);
sys2.freq
ans =
1.1000
You can also combine model extraction through frequencies with indexing into
the I/O dimensions. For example, if
sys is an FRD model with two inputs, two
outputs, and frequency vector
[2.1 4.2 5.3],withsys.Units specif ied in
rad / s, the n
sys2 = sys(1,2,'freq',1)
specifies sys2 as a SISO FRD model, with one frequency data point, 2.1 rad/s.
Referencing Channels by Name
You can also extract subsystems using I/O group or channel names. For
example, if
sys has an input group named noise, consisting of channels two,
four, and five, then
sys(1,'noise')