How can I use 'name' to specify input/output pairs between two systems connected in an LFT arrangement?

Hi all,

I have two systems (state-space form) that I wish to connect together in a Redheffer star product arrangement (generalisation of the LFT), and wish to name the inputs/outputs somehow such that I can specify which inputs are connected to which outputs etc.

This is due to the fact that I have one system with 30 outputs and inputs, and another with 31 outputs and inputs. I wish to connect in an LFT configuration the 30 inputs/outputs of the first system with a particular 30 of the 31 inputs/outputs of the second system - i.e. reducing the overall combination of systems to a 1-input-1-output system.

The input & output of the second system that I wish to 'leave out' of the LFT connection is a specific one, but I don't know how to use the LFT command in such a way that I can specify it to NOT be connected - I need to somehow be able to label the inputs and outputs as such that I can use these names to specify connections. Does anyone know how to do this?

Kind regards, Olie

Answer 1

[Carla]

If I understand what you want to do, you can assign values to the InputName and OutputName properties of your state-space models. Then instead of LFT (which just connects up the first n inputs), you can use the CONNECT command. CONNECT automatically looks for signals with matching InputName and OutputName values and joins them up, leaving other signals unconnected.

So, for example,

G1 = rss(3,3,3); % arbitrary 3-state, 3-input, 3-output system
G1.InputName = {'a','b','c'};
G1.OutputName = {'y'}; % Optionally, you can use a vector valued assignment 
% These are automatically expanded into {'y(1)','y(2)','y(3)'}

G2 = rss(3,4,4); % 3-state, 4-input, 4-output system
G2.InputName = {'y(1)','y(2)','unconnectedinput','y(3)'};
G2.OutputName = {'a','unconnectedoutput','b','c'};
% Give the inputs of G2 names that match the G1 outputs that will connect to them 
%(change the order if necessary, such as {'y(2)','y(3)','unconnectedinput','y(3)'})
% Likewise give the outputs of G2 names that match the corresponding G1 inputs

T = connect(G1,G2,'unconnectedinput','unconnectedoutput')
size(T) % 1-input, 1-output 6-state system 
        % T has input 'unconnectedinput' and output 'unconnectedoutput'

Have a look at

 doc connect

And at this example: http://www.mathworks.com/help/control/ug/build-a-model-of-a-multi-input-multi-output-mimo-control-system.html

Hope this helps.

[Oliver]

Thanks Carla, this looks promising.

Olie