non linear fitting of two parameter, one parameter is never changing ...

Hello, I am doing a non linear fit, my model is like this:

a = K * quad(@(x)(besselj(1.5,x)).^2 .* x./(x.^4 + t.^2) )

fitting parameters are "K" and "t". it is working fine, but it seems to fit only "t" and gives back "K" the same as I entered as the initial value. When I change K's initial value, the same value is given back but with different "t". Why this discrimination is happening?

Answer 1

[Daniel Armyr]

Assuming you use fminsearch, it will only optimize on the variable x. If you want to optimize on more than one variable, you have to make x a vector, and then replace x with x(1) and t with x(2).

If you read the lower part of the documentation for fminsearch, it will tell you this, but I myself allways mess up when doing this because I forget you can only have one variable to optimize on.