Specifications

3 Operations on LTI Models
3-8
sys2.Frequency
ans =
1.1000
1.2000
displays the second and third entries in the frequency vector.
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 specified in rad/
s, then
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')
is equivalent to
sys(1,[2 4 5])
Similarly, if pressure is the name assigned to an output channel of the LTI
model
sys,then
sys('pressure',1) = tf(1, [1 1])
reassigns the subsystem from the first input of sys to the output labeled
pressure.