Curve fitter app with custom function

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HYZ 2022-9-2

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https://ww2.mathworks.cn/matlabcentral/answers/1793800-curve-fitter-app-with-custom-function

评论： Walter Roberson 2022-9-6

采纳的回答： Walter Roberson

Hi, I have a gaussian function y=A*exp(-(x-mu).^2/(2*sigma^2)).

I want to use custom equation in curve fitter. The default setting in the custom equation is a*exp(-b*x)+c.

How should I key in mu and sigma in custom equation? I put "a*exp(-(x-b).^2/(2*c^2))" but the curve doesn't look correct.

I used Gaussian option with 'gauss2' and the curve looks fine but the equation for gauss2 is not exactly same as my custom function. that's why I want to use custom function. Please advise.

thanks.

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Walter Roberson 2022-9-2

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在 MATLAB Online 中打开

If you are using cftool, then when you get to the place to enter the custom equation, you can just enter

A*exp(-(x-mu).^2/(2*sigma^2))

and it will estimate all of the parameters.

Note: you might want to consider adding a constant term to the equation.

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HYZ 2022-9-3

Hi Walter, thanks a lot for explanation. I changed the Lower bound for a1 to 0. I got a better fitted graph with these coefficients.

though a2 is reduced to around 180 as you said, a1 is pretty higher than the raw data.

a1 = 1.583e+06 (-5.126e+08, 5.158e+08)

b1 = 706.8 (-1.249e+04, 1.391e+04)

c1 = 129.7 (-1933, 2192)

a2 = 179.6 (-466.8, 826.1)

b2 = 121.9 (77.94, 165.9)

c2 = 23.27 (-31, 77.53)

Actually, I am following the below bold method for fitting. I don't think I can find equal width sigma using cftool. could you please suggest? I first time use Gaussian fitting so I am quite lost. thanks again for your help.

Walter Roberson 2022-9-6

I would suggest constraining b1 as well to positive... keep constraining more variables to positive until you stop getting coefficients that cross 0 in the confidence bounds.

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