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    <p>You already got the right idea, I don't know where you got stucked. Here is the code which solves your problem, I tested it, its works fine. Be aware that a simpler input probably gets you better results, that means for example a single step instead of a square wave.</p> <pre><code>% load your data (text file with your two columns) load data.txt; % sample index, reducing of input to get single step instead of square wave x = 1:1:length(data); data(x &gt; 2900,:)=[]; x(x &gt; 2900)=[]; % plot data figure(1) plot(x,data(:,1)); hold on plot(x,data(:,2)); hold off % prepare data for tftest, 100 is a random chosen sampling time tfdata = iddata(data(:,1),data(:,2),100); % estimate system, factor 5 -&gt; number of poles (variable as desired) sys = tfest(tfdata,5); % plot step response (factor 5 comes from input) figure(2) step(5*sys) </code></pre> <p>Edit: the output for number of poles np=5:</p> <pre><code>sys = From input "u1" to output "y1": -3.337e-05 s^4 + 1.326e-07 s^3 + 1.639e-11 s^2 + 1.221e-14 s + 1.064e-19 ---------------------------------------------------------------------------- s^5 + 0.005287 s^4 + 1.516e-06 s^3 + 4.517e-10 s^2 + 2.896e-14 s + 2.037e-19 </code></pre> <p>Edit#2: in your previous question you were asking whether it would be better to use <code>idfrd</code> or <code>iddata</code> - but do you actually have the frequency response data? I actually don't think it should make a big difference, if you choose the number of poles high enough. Just try out what it's working better for you. The workaround is the same.</p>
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    1. POEstimate transfer function from input output data
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    1. USTry Hard
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    1. CO+1 for the pain in the … to download data and help the someone else
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    2. COthanks ;) I expected to have the same problem quite soon, so I could try it also now.
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    3. COI was expecting (np=1): sys = 19.71 / ( s + 7.8125 ). Why are the coefficients so small when using MATLAB tfest?
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      1. USMatt1993
 

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