Fitting an Amplitude-Response Curve
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Chinwe Orie
le 23 Fév 2019
Commenté : Chinwe Orie
le 6 Mar 2019
Hi,
I'm trying to fit an amplitude-frequency response curve to a particular equation (in picture below).
![example.jpg](https://www.mathworks.com/matlabcentral/answers/uploaded_files/205466/image.jpeg)
![equation pic.png](https://www.mathworks.com/matlabcentral/answers/uploaded_files/205467/image.png)
I've tried using code to do it but I keep getting the following:
f1 = fittype( @(F, w0, g, m, w) F.*(cos(m.*(w0.^2-w.^2)./sqrt(m.^2*(w.^2-w0.^2).^2 + g.^2*w.^2)))....
./sqrt(m.^2*(w.^2-w0.^2).^2 + g.^2*w.^2), 'independent', {'w'},...
'dependent', {'y'} );
![failedattempt.jpg](https://www.mathworks.com/matlabcentral/answers/uploaded_files/205468/image.jpeg)
Also, I get a warning which says, "Warning: Start point not provided, choosing random start point." What does this mean?
Thanks!
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Réponse acceptée
Rishabh Gupta
le 4 Mar 2019
Hi Chinwe,
Generally Curve Fitting and Optimizations algorithms require you to give a starting point satisfying all your contraints(if any) from where the algorithms starts its logic and tries to find the best fit/best solution. In this case, you did not specify the starting point, hence the warning. But the algorithm needs a starting point, therefore it chooses a random starting point. Howecver this is not an error and may not affect your algorithm/results much. Please note in some case choice of starting point affects the solution.
I hope it was helpful.
Thanks
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