Fitting the curve problem

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Yumeng Yin 2022-3-10

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1668144-fitting-the-curve-problem

评论： Sam Chak 2022-3-10

Ch4.mat

I try to fit an s-shape curve with the function that I define. Actually I get a not-so-bad fitting by setting a more appropriate boundary and starting point. One remaining question is that although the fit is better, the parameters' range is still big. Anyone has any advice for this? Attached file is the data file for Ch4.

Final_time=10;
recordLength=size(Ch4);
recordLength=recordLength(1);
Time=[linspace(0,Final_time*1000,recordLength)]';
Ch4_mV=Ch4.*1000;
[pks,locs]=findpeaks(Ch4_mV,'MinPeakProminence',30);
for j=3
   duration_fit=Time(locs(j)-6:locs(j)+10);
   y_duration_fit=Ch4_mV(locs(j)-6:locs(j)+10);
   FitFunction=@(a,b,A,B,F,e,x)F.*(b.*A-(x-a).*B)./((x-a).^2+b^2)+e;
   options=fitoptions('Method','NonlinearLeastSquares','Upper',[Time(locs(j)+50) Time(8)-Time(1) 1 1 pks(j)+10 0],'Lower',[Time(locs(j)-50) 0 -1 -1 pks(j)-10 -15],'StartPoint',[Time(locs(j)),1,1,Time(locs(j)+5)-Time(locs(j)-2),pks(j),1]); 
   [fitcurve,gof]=fit(duration_fit,y_duration_fit,FitFunction,options)
   plot(fitcurve,duration_fit,y_duration_fit);
end