Hi, You can not call any overloaded C++ operators from TTreeFormula. Hence (p4_pi1_eta_rec_fit + p4_pi2_eta_rec_fit) is not a valid TTreeFormula expression. In addition, TTreeFormula can currenlty only call function that takes and returns numerical values. Cheers, Philippe. -----Original Message----- From: owner-roottalk@pcroot.cern.ch [mailto:owner-roottalk@pcroot.cern.ch]On Behalf Of Francesco Perfetto Sent: Tuesday, June 15, 2004 10:45 AM To: roottalk@pcroot.cern.ch Cc: rene.brun@cern.ch Subject: [ROOT] how draw the .M() of the sum of TLorentzVector Hi all, I would like add 2 or more TLorentzVector for then take the .M(). After I open my root file with TBrowser in which there are the TLorentzVector I do at command line: root [1] .L $ROOTSYS/lib/libPhysics.so root [2] res->Draw("(p4_pi1_eta_rec_fit + p4_pi2_eta_rec_fit).M()") (WHERE p4_pi1_eta_rec_fit. and p4_pi2_eta_rec_fit. are 2 my TLorentzVector) but I have the following error: *ERROR 30 : Bad numerical expression :"(p4_pi1_eta_rec_fit+p4_pi2_eta_rec_fit).M()" root [3] There is anyone that can help me? Thanks in advance. Francesco.
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