How to fit with non-function

Can you please help.
I want to fit (x,y) data points (with errors bars of delta_x and delta_y) with:
f(x) = par(0) + par(1) * F1 + par(2) * F2
where F1 and F2 are functions, but they are complex itnegral functions, so I don’t write them in root. But I do have the values of F1 and F2 for all experimental data points x. So my functions F1 and F2 are in fact a list of values.
Can you suggest how to fit in order to extract the parameters p(0), p(1) , p(2) and their error bars?


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@couet can you please help here?


You will need you make you own fitting function and access the data for F1 and F2 in it.

Do you maybe know a link to such an example? I am still unsure how to make the function and the fit.

May be @moneta has one.