Grey-box estimation in frequency domain using greyest

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Thor on 25 Jul 2013

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https://se.mathworks.com/matlabcentral/answers/83127-grey-box-estimation-in-frequency-domain-using-greyest

Commented: Perry on 23 Jan 2017

I'm trying to do grey-box estimation in the frequency domain with matlab function greyest.

sys = greyest(data,idgrey_object)

Based on the documentation of greyest, 'data' should be either time-or frequency domain data.

I have some measured data that I'm using 'tfestimate' and further 'frd' to represent the data in the frequency domain. I have made a 'idgrey' model based on what I known about the system, just simplified.

When I know do the greyest-call it produces:

Undefined function 'greyest' for input arguments of type 'frd'.

Here an example for simplicity, based on the Example: Estimate Grey-Box Model:

 N =256;
 [tfdata,f] = tfestimate(u(2:end,1),y(2:end,1),hann(N),[],[],1000);
 tf1 = frd(tfdata(2:end-1),f(2:end-1),'units','Hz');
 [tfdata,f] = tfestimate(u(2:end,1),y(2:end,2),hann(N),[],[],1000);
 tf2 = frd(tfdata(2:end-1),f(2:end-1),'units','Hz');
 Hresp = zeros(2,1,length(tf1.Frequency));
 Hresp(1,1,:) = reshape(tf1.ResponseData,1,length(tf1.Frequency));
 Hresp(2,1,:) = reshape(tf2.ResponseData,1,length(tf2.Frequency));
 frddata = frd(Hresp,tf1.Frequency,'FrequencyUnit','Hz');
 G = 0.25; 
 tau = 1; 
 init_sys = idgrey('motor',tau,'cd',G,0);
 sys = greyest(frddata,init_sys);