The ranking on input variables (method unspecific) is derived using the separation formula, defined as in equation 1 of TMVA Users Guide page 25. I have a simple question. Why there is a factor 1/2 in that formula. Could you please explain to me.
Thanks a lot for your help in advance!
I guess you are referring to the formula defining the separation of a classifier.
In this case you need a factor of 1/2 if you want S to be defined witting 0 and 1. In case the signal and background classifier PDF y are completely separated it is easy to show that the integral will be just the sum of the integral of the two pdf’s, which by definition is 1 + 1 = 2.
So you need a factor 1/2 before.
Ok, I understand. Thank you.