When you use TTree::Draw function, TTreeFormula objects are created.
As you say these objects know which variables are referenced.
If you look (in the pretty complex!) logic of TTree::EventLoop,
you will see how only referenced branches are read.
I understand that you would like a new function setting automatically
the branch status active for only the branches referenced in all
the expressions.
> BTW, Rene, what is the email address of CERNLIB team ? I want to send
> suggestion on creating CERNLIB with PIC option at HP-UX. Thanks.
I was surprised to see that it took me many clicks on the Web
to find this info. At the end, I believe that I found the right info.
Try heplib.support@cern.ch
Rene Brun