lft
Generalized feedback interconnection of two models (Redheffer star product)
Syntax
lft
sys = lft(sys1,sys2,nu,ny)
Description
lft
forms the star product or linear fractional transformation (LFT) of
two model objects or model arrays. Such interconnections are widely
used in robust control techniques.
sys = lft(sys1,sys2,nu,ny)
forms the star product sys of the two models (or
arrays) sys1 and sys2. The star
product amounts to the following feedback connection for single models
(or for each model in an array).
This feedback loop connects the first nu outputs
of sys2 to the last nu inputs
of sys1 (signals u), and the
last ny outputs of sys1 to the
first ny inputs of sys2 (signals y).
The resulting system sys maps the input vector
[w1 ; w2]
to the output vector [z1 ; z2].
The abbreviated syntax
sys = lft(sys1,sys2)
produces:
The lower LFT of
sys1andsys2ifsys2has fewer inputs and outputs thansys1. This amounts to deleting w2 and z2 in the above diagram.The upper LFT of
sys1andsys2ifsys1has fewer inputs and outputs thansys2. This amounts to deleting w1 and z1 in the above diagram.
Limitations
There should be no algebraic loop in the feedback connection.
Algorithms
The closed-loop model is derived by elementary state-space manipulations.
Version History
Introduced before R2006a
