Problem: fit function change the size of my "x" data-array.

I've written the following fitting code to fit a sin curve function for different regions with different phase offset, while keeping a constan period frequency. My problem is that the fitting function changes the size of my x array to size (7), whereas I know that it has length(x)=4000;

Note: I put it all in a seperate function to clear up my main code.

function output=envelope_theory_fitting_Regionalized(x, signal)
% define anonymous function
interferometer_off_regionalfit=@(period,phase1,phase2,phase3,x) interferometer_off_regional(period,phase1,phase2,phase3,x);

% use the fitting function 
output_region=fit(x,signal,interferometer_off_regionalfit,'Robust','Bisquare')%,'Lower',lb,'Upper',ub)

end


function output=interferometer_off_regional(period,phase1,phase2,phase3,x)

regions=[1,1901;1902,2307;2308,length(x)];

x1=x(regions(1,1):regions(1,2));
output1=(sin((period*x1+phase1)/2).^2);

x2=x(regions(2,1):regions(2,2));
output2=(sin((period*x2+phase2)/2).^2);

x3=x(regions(3,1):regions(3,2));
output3=(sin((period*x3+phase3)/2).^2);

output=[output1;output2;output3];

end

While stopping in debbuging mode within my fitting function I notice that length(x)=7

x=
0.1250
0.2500
0.3750
0.5000
0.6250
0.7500
0.8750

which is also the error that I retrieve in the console.

Error:Index exceeds the number of array elements (7).

Hope that anyone knows! or have encountered this problem.

Answer 1

[Cris LaPierre]

It appears the fit first performs a 'sanity check' of the input function using 7 values. If that passes, it then actually runs the fit on the actual input. Basically, fit was not designed to work with piecewise functions, which is essentially what you are trying to do.

I'm not sure if the results are meaningful, but one workaround is to write your code in a way that works for the sanity check as well as the actual data. Since we con't have your data, just be aware that this is untested.

output_region=fit(x,signal,@(period,phase1,phase2,phase3,x) interferometer_off_regional(period,phase1,phase2,phase3,x))%,'Lower',lb,'Upper',ub)


function output=interferometer_off_regional(period,phase1,phase2,phase3,x)
if length(x)==7
    output = x;
else
    regions=[1,1901;1902,2307;2308,length(x)];

    x1=x(regions(1,1):regions(1,2));
    output1=(sin((period*x1+phase1)/2).^2);

    x2=x(regions(2,1):regions(2,2));
    output2=(sin((period*x2+phase2)/2).^2);

    x3=x(regions(3,1):regions(3,2));
    output3=(sin((period*x3+phase3)/2).^2);

    output=[output1;output2;output3];

end
end

[Mathias Staunstrup]

Thanks Cris it seems to work for me!