Update Entry in TTree branch

[couet]

This question was already asked on this forum, for instance here:

Multiplying a Branch with a coefficient

[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 $ROOT…