how to get the parameters of step response?

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UPT
UPT 2012-11-27
hi everybody.. how can get 'num' and 'den' when i have the step response? i'm using matlab 2010. please help me.thank you.

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回答（2 个）

Ryan G
Ryan G 2012-11-27
You can use the system identification GUI to analyze data and estimate a transfer function from that data. In this case you are using step response data so the input would be the step and the output would be the response.
See the system identification GUI
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UPT
UPT 2012-11-27
Ryan G,thanks for answering. i did a mistake in my question. i have transfer function and not step response...:/
Ryan G
Ryan G 2012-11-27
If you have a transfer function, say sys, you can obtain the num and den like this:
sys = tf(1,[1 1]); %demo transfer function
num = sys.num;
den = sys.den;

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Rajiv Singh
Rajiv Singh 2012-11-27
To elaborate on what Ryan wrote, suppose y is the vector of step response data and Ts is the sampling time.
N = length(y);
u = [zeros(10,1); ones(N,1)];
y2 = [zeros(10,1); y];
stepdata = iddata(y,u,Ts);
model = tfest(stepdata, numpoles, numzeros); % available >=R2012a
where numpoles and numzeros are the desired number of poles and zeros for the transfer function.
[num,den] = tfdata(model); % or, simply do model.num and model.den
The zero-padding of the data was done to ensure that the step transition (0 to 1) is evident in the data.
Rajiv
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UPT
UPT 2012-11-27
rajiv thank you for your opinion. i have transfer fuction and not step response. could you help me?thanks
Rajiv Singh
Rajiv Singh 2012-11-27
[num,den] = tfdata(model), or, simply do model.num and model.den where model is the transfer function

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