MATLAB: Function returning matrix instead of vector

functionleast squares curve fitting

Hello,

I have made a function for use in least squares curve fitting of the form:

f=@(xf,xdata)xf(1)*(xf(4)+((xf(2)-xdata)/(xf(3)/2))).^2/(1+((xf(2)-xdata)/(xf(3)/2)).^2)

xf should have 4 parameters

When I test the function with

f(x0f,xdata)

with x0f = [1.0000, 462.7580, 1.8007, 0], and xdata a 15×1 column vector I get a 15×15 matrix as output, when I expect a 15×1 column vector. I believe the issue is that the f function has xdata squared (.^2) both in the numerator and denominator, but I don't know how to circumvent this as there is no way to isolate xdata. Any help is appreciated.

Best Answer

Read about element by element operations.

Repalce * with .*, / with ./

f=@(xf,xdata)xf(1)*(xf(4)+((xf(2)-xdata)./(xf(3)/2))).^2./(1+((xf(2)-xdata)./(xf(3)/2)).^2) ;

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MATLAB: How to take two inputs simultaneously from the user

x=input('Enter range of x :');
xf1 = x(1) ;
xf2 = x(2) ;

Also have a look on deal.

MATLAB: Simultaneously fit multiple data sets — with one of the fit parameters common between all data sets.

I don't think you're far off. If you have m fits of n parameters each, with one parameter the same across all m fits, then you have a total of 1 + m*(n-1) parameters. So in the example you posted, x0 should have 1 + 2*(8-1) = 15 elements. You should modify fitfun slightly, too

x2 = x([9 2 10 11 12 13 14 15]);

otherwise the 10th element is left out of the fit entirely.

To keep yourself sane as you extend to 5 fits, it might help to reorder/renumber the parameters. I'd even be tempted to change voigt1 to be a function of two inputs v (scalar) and x (7-element vector). Then fitfun would look something like

    function error = fitfun(x)
        v  = x(1);
        x1 = x(2:8);
        x2 = x(9:15);
        y1 = voigt1(v,x1);
        y2 = voigt1(v,x2);
        error = sum((ydata1-y1).^2 + (ydata2-y2).^2);
    end

This would be more easily adapted to 5 (or whatever) fits.

It looks like there might be an issue with passing xdata and ydata into the functions. You can use anonymous function handles to help with that, by making the function file accept an extra input, then making an anonymous function handle with the extra input fixed:

   function error = fitfun(x,ydata1,ydata2)
     ...
   end
   x0 = ...
   ydata1 = ...
   ydata2 = ...
   f = @(x) fitfun(x,ydata1,ydata2)  % ydata1 and ydata2 are defined in the local workspace
   fminsearch(f,x0)

Best Answer

Related Solutions

MATLAB: How to take two inputs simultaneously from the user

MATLAB: Simultaneously fit multiple data sets — with one of the fit parameters common between all data sets.

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