Is the 8th term maximum in the curve fitting toolbox and command line?

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재열 김
재열 김 2022-5-23
编辑： Matt J 2022-5-23
It seems to apply up to 9th term with a simple command line input.
From 'sin10', it is recognized as 3D. is there any other way?
I hope for your answer. thank you.
F = fix(x,y,'sin9')
plot(F,x,y)

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回答（2 个）

Matt J
Matt J 2022-5-23
You will probably have to use a custom model, or else resort to lsqcurvefit().
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재열 김
재열 김 2022-5-23
@Jongil Lee
Thank you for answer. I'd like to get a startpoint that is optimized equal to the sum of sine model.
However, the startpoint for a custom nonlinear model is arbitrary.
Of course I can input the coefficients directly, but I can't find the appropriate coefficient values.
So I want to know how to get an optimized startpoint.
thanks!
Matt J
Matt J 2022-5-23
编辑：Matt J 2022-5-23
For a startpoint, perhaps do a non-custom 'sin8' fit to estimate the first 24 parameters. Subtract the sin8 fit from the measured curve samples to obtain a a modified set of curve samples to which you would do a non-custom 'sin2' fit to estimate the remaining parameters.
F=fit(x,y,'sin8');
dy=y-F(x);
dF=fit(x,dy,'sin2');
startpoint=[coeffvalues(F),coeffvalues(dF)]; %startpoint for custom sin10 fit

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Matt J
Matt J 2022-5-23
Perhaps just do an FFT decomposition and select the 10 strongest frequencies.

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