Specifications

Extracting and Modifying Subsystems
3-9
You can reference a set of channels by input or output name by using a cell
array of strings for the names. For example, if
sys has one output channel
named
pressure and one named temperature,then thesetwooutputchannels
can be referenced using
sys({'pressure','temperature'})
Resizing LTI Systems
Resizing a system consists of adding or deleting inputs and/or outputs. To
delete the first two inputs, simply type
sys(:,1:2) = []
In deletions, at least one of the row/column indexes should be the colon (:)
selector.
To perform input/output augmentation, you can proceed by concatenation or
subassignment. Given a system
sys with a single input, you can add a second
input using
sys = [sys,h];
or, equivalently, using
sys(:,2) = h;
where h is any LTI model with one input, and the same number of outputs as
sys. There is an important difference between these two options: while
concatenationobeystheprecedencerules(seepage2-5),subsystemassignment
does not alter the model type. So, if
sys and h are TF and SS objects,
respectively, the first statement produces a state-space model, and the second
statement produces a transfer function.
For state-space models, both concatenation and subsystem assignment
increase the model order because they assume that
sys and h have
independent states. If you intend to keep the same state matrix and merely
update the input-to-state or state-to-output relations, use
set instead and
modify the corresponding state-space data directly. For example,
sys = ss(a,b1,c,d1)
set(sys,'b',[b1 b2],'d',[d1 d2])