Problem with fit-convergence


I’m trying to fit a resonance-curve and know the approximate magnitude of my parameters, but my function just does’nt want to fit. I had another set of data, which I got fitted after some trial & error, but with this, it just does not work. i tried fixing some, adjusting the range, and setting different initial values. any other suggestions or fundamental advice?

p1 sould be around 1e10, p2 around 1e3, the code is attached

ps: i run root 5.17 with ubuntu 7.10
nicht-lin_neu.txt (479 Bytes)
nicht-lin_neu.cpp (1.7 KB)


are you sure the definition of your function is correct ?
It looks to me a bit bizzarre. If I try to fit with a simple breit-wigner the fit works fine.
I would re-define your function and put for example as a parameter the location of the maximum.

Best Regards


we derived this function from general assumptions and it did fit for the first data set, so it should be the real one. anyway, i will check this, thanks for your hint