For fminsearch: ??? Attempted to access params(3); index out of bounds because numel(params)=2.

Hi, the objective of the code below is to use fminsearch function for curve fitting purposes so that I will be able to get unknown parameters T1,T2 and C by plotting xdata against ydata which I already have in my database.

I have previously managed to find the value of parameters T1 and T2. However, when I introduced another third parameter C, I could got this error which I could not resolve:

??? Attempted to access params(3); index out of bounds because numel(params)=2.

Below is the code:

--------------------------------------------------------------------------------------------------------------------------------------- FUNCTION CODE:

function [estimates, model] = fmmintest(xdata, ydata) % A random starting point for fminsearch. start_point = rand(1, 2, 2); model = @expfun; estimates = fminsearch(model, start_point);

    function [sse, FittedCurve] = expfun(params)
        T1 = params(1);
        T2 = params(2);
        C = params(3);

        FittedCurve =C{(T2^2)*(sin(xdata)).^4 +(T1^2)*(cos(xdata).^4)};  
        FittedCurve = cell2mat(FittedCurve);
        ErrorVector = FittedCurve - ydata;
        sse = sum(ErrorVector .^ 2);
    end
end

Any help will be much appreciated ! Thanks !!

Regards

Answer 1

[Matt J]

If you have only 3 parameters, why do you have 4 elements in your start_point array?

    >> start_point=rand(1,2,2);  numel(start_point)

    ans =

         4

That wouldn't account for the error you're seeing, however.

I'm a bit skeptical that we're seeing your exact code. It sounds like you're initializing somehow using the previous code with numel(start_point)=2

Answer 2

[Sean de Wolski]

rand(1,2,2) will create a 1x2x2 array. Perhaps you meant rand(1,3)?

Answer 3

[Shing]

Yes, I made a terrible mistake. I should put rand(1,3) instead. Thank you Sean and Matt!

And Matt, could you please elaborate on what you are skeptical about, I don't quite get what you mean about the initializing part. I previously did the code for two parameters only, and now I'm including the third parameter C.Thank you !

[Matt J]

In the error message that you showed us, numel(params)=2 implies that fminsearch thought that you were are solving a 2-parameter problem. fminsearch deduces this from numel(start_point). But in the code you showed, numel(start_point) was equal to 4. I therefore cannot see how it would have assumed you were working in R^2 if the code you showed us was actually the code being run.