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Compare tf function with x-y data

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Jason Baxter
Jason Baxter on 8 Aug 2013
I have an ss function object and I want to plot the magnitude against frequency of the object (which I can view using ltiview) along side experimental data. The experimental data is in the form of frequency points in column 1 and magnitude points in column 2, is there some way I can get the ss object data in the same form so I can plot them on the same graph?

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dpb
dpb on 9 Aug 2013
What is an ss function object and a tf function?
Jason Baxter
Jason Baxter on 12 Aug 2013
an ss function object is a state space object, I think it comes in the Digital System processing toolbox toolbox (DSP). A tf function is a transfer function object that also comes with the DSP toolbox
dpb
dpb on 12 Aug 2013
Don't have the toolbox so all I can do is read the doc's. I'd presume like most other toolboxes they must be structures and you should be able to use normal Matlab structure addressing to return the data into arrays but that's guessing.
I'd suggest changing you tags to DSP Toolbox and perhaps 'toolbox objects' or somesuch; the rest you have are meaningless and unrelated to the problem space. As can be seen by my confusion, not everyone else will have the same background and be able to infer what abbreviations are...help the prospective responder from the git-go.

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Answers (1)

Arkadiy Turevskiy
Arkadiy Turevskiy on 12 Aug 2013
Edited: Arkadiy Turevskiy on 13 Aug 2013
You get magnitude and phase of an LTI object (ss,tf,etc) by using bode command.
If you have your frequency vector, w, and your ss object sys, then:
[mag,ph]=bode(sys,w);
so now you have your two columns, w and mag

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Jason Baxter
Jason Baxter on 13 Aug 2013
ah, knew it would be something simple. It was an either know it or you don't case.
Thank you Arkadiy Turevskiy

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