Please help fitting

Hello Rooters.

I drew the following picture.


I want to fit like a blue line and I want to know the function to get as a result of the fitting.

please help…

Through 3 points many functions can be used. It is up to you to decide which one is the most
appropriate for you particular problem.

This seems more a question you should ask to your supervisor.
If I should guess, I would say it’s how the resolution of a calorimeter vary with the energy.
In that case the correct function is

TF1 *f= new TF1("f","TMath::Sqrt(  TMath::Pow([0] ,2) + TMath::Pow([1]/TMath::Sqrt(x) ,2) +   TMath::Pow([2]/x ,2)     )")

Look here EM Calorimeter