I am not sure to understand what you want to do.
If you simply want to histogram Q2 multiplied by a coeeficient or
any other transformation, do
mytree.Draw(“Q2”); //to draw the original Q2
mytree.Draw(“1.234*Q2+5.678”);
Please read the Users Guide and the tutorials relates to Trees.
[quote]But, as I have read somewhere else in the forum, it is impossible (or “not recommended at all”) to do something like Q2 = Q2*A [/quote]It is possible but not recommended since the step to do so are not trivial.
[quote]So, I need to find another way to do this, with as few steps as possible. [/quote]Simply create a new tree, with just the branch Q2 and make this new tree a friend of the first tree (oldtree->AddFriend(…) ).
Alternatively, Clone the old tree and add a new branch (See $ROOTSYS/tutorials/copytree3.C)