I have fitted my data using the matlab build in fitting function, such as 'exp2'. Since those build in functions did not work perfectly for all of my data, I tried using anonymous functions to fit my data. I could not get good results, so i tried to add the 'exp2' function as an anonymous function and compare it to the original build in 'exp2' function:
xdata = [5 10 20 40 80 100 150 200 250];
ydata = [2 6 12 20 30 40 50 70 100];
fitfun = @(a,b,c,d,x) a*exp(b*x) + c*exp(d*x);
[f,goodness] = fit( xdata, ydata, fitfun, fitoptions('exp2'))
coeffs = coeffvalues(f)
In combination with:
[f2,goodness] = fit( xdata, ydata, 'exp2')
coeffs = coeffvalues(f2)
The results were almost always very different and the fit of the anonymous function was almost always very crappy. The fit with the build in 'exp2' function was fine.
So I want to know:
- 1) What is the essential different between my anonymous 'exp2' function and the build in 'exp2' function
- 2) What do I have to do to get good fitting values with my anonymous functions? Not only this one, but also other functions I want to try.