Fitting an Amplitude-Response Curve

Hi,

I'm trying to fit an amplitude-frequency response curve to a particular equation (in picture below).

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'} );

Also, I get a warning which says, "Warning: Start point not provided, choosing random start point." What does this mean?

Thanks!

Answer 1

[Rishabh Gupta]

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

[Chinwe Orie]

In this case, the starting point did matter! I adjusted it and works fine now. Thanks!