Out of curiosity, I wanted to find more about the separation <S^2>, corresponding to equation (1) in section 3.1.10 in the TMVA User’s Guide. The reference  that the Guide links to appears to now be a dead link, so I haven’t been able to reference the thesis it appears to come from. So far I also haven’t been able to find elaboration about it in “The BABAR Physics Book”.
I would like to know if “separation” goes by a statistical distance name. A cursory look at Wikipedia leaves me wondering if it relates to “Energy distance”, and why it is used over “Hellinger distance”. The separation appears to return values closer to 1 than the Hellinger distance would.