The definition of Breit-Wigner function in the evaluate method of ROOT: roofit/roofit/src/RooBreitWigner.cxx Source File is incorrect, as can be double checked with ROOT: math/mathcore/src/TMath.cxx Source File . Is there any possible issue that it might cause?
Hi,
Thanks for this observation.
The definition is not wrong. One of the most powerful features of RooFit is the normalisation of the pdfs, which happens elsewhere. No need to add more constants in the evaluate method, it would just be a performance hit.
Speaking of which, the division by 4 in the TMath implementation is a performance hit (CPUs are not very efficient with divisions). Since you highlighted this function, would you be willing to take credit with a PR optimising the division by 4 into a multiplication by 0.25?
Cheers,
Danilo
The correct equation has one of the parameters gamma in the numerator, which the RooBreitWigner doesn’t.
I would also like to add that using RooBreitWigner and TMath Breit-Wigner gives the same fit results.