Using Parameters in TTreeFormula's?

Hi,

Are there plans to permit normal TFormula parameters in an expression using a TTreeFormula? For instance, I'd like to write something like:

TTreeFormula totEdiff("totEdiff",

                      "electronP-([0]*preshowerE+[1]*showerE)",tree);

where 'electronP', 'preshowerE' and 'showerE' are simple leafs in tree. This can be done in TFormula's, but does not appear to work in TTreeFormula's. In TTreeFormula::DefinedVariable fNpar is set to 0 and the class never looks back.

I'm trying to write a general routine to minimize expressions in terms of tree variables by varying the set of parameters, but the TTreeFormula's are completely unaware of the normal '[0]'-like parameters. I know it can by minimized by writing a macro using TFitter and TMinuit directly, but I'd like to have a more general implementation since this is common task. It could even evolve into a TTree::Minimize kind of method.

Thank you,
Rob Feuerbach

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