TChain->AddFriend(TTree,File)

ROOT
1

Good day,

The idea is to build TChain and then AddFriend to it (with a Tree of different structure than TChain trees) and then to plot one branch of TChain vs. One branch of TTree. Below is a piece of code used:

//--> building the TChain;
   TChain *fullNtps = new TChain("RootNtp");

   while(!files_in.eof()) { //-- Add files to TChain from the list of files;
         files_in.getline(fName,fNLength);
         fullNtps->Add(fName);
   };
   files_in.close();
   fullNtps->SetName("fullNtps");  //-- to avoid that TChain and TTree from calibntps_xxx file have the same name;
//<-- TChain is constucted;

   TChain *cloneNtps = (TChain*)fullNtps->Clone();   //-- clone TChain;
   TFile *calibF = new TFile(fileName);              //-- open Tree file;
   TTree *calibNtps = (TTree*)calibF->Get("RootNtp");

   Double_t Y1max = calibNtps->GetMaximum("WienerAmpl_chaleur")); //-- to find maximum;
   cloneNtps->AddFriend("RootNtp",fileName);
   Double_t Y2max = cloneNtps->GetMaximum("RootNtp.WienerAmpl_chaleur"));

The problem is that variables Y1max and Y2max are different, while expected to be exactly the same!
TChain though has itself branch “WienerAmpl_chaleur” but it also shows (in TreeViewer) “RootNtp.WienerAmpl_chaleur” after AddFriend() is exectued. However, both of them contain exactly the same data and different one from calibNtps->WienerAmpl_chaleur.

Did I miss something/did wrong in AddFriend() action?

ROOT 5.18, Linux SuSE 10.3, gcc (GCC) 4.2.1 (SUSE Linux)

2

Hi,

The TChain still get confused about which ‘Tree’ you are referring to in the AddFriend. So just make it explicit by passing the pointer:cloneNtps->AddFriend(calibNtps); // Or is it AddFriend(fullNtps) ? And since the main tree and the friend have the same name, set a Tree Friend Alias name to be able to disambiguate which one you are referring to in the formulas.cloneNtps->AddFriend(calibNtps,"aliasToFriend"); .... Double_t Y2max = cloneNtps->GetMaximum("aliasToFriend.WienerAmpl_chaleur"));

Cheers,
Philippe.

PS. Why do you need to introduce the ‘clone’ of the TChain?

3

Thank you! It gets better, at least now after

if I compare:

calibNtps->Draw("WienerAmpl_chaleur"); cloneNtps->Draw("calib.WienerAmpl_chaleur");

I get the same plots but still

cloneNtps->GetMaximum("calib.WienerAmpl_chaleur"); calibNtps->GetMaximum("WienerAmpl_chaleur");
give different output and even now different from

cloneNtps->GetMaximum("WienerAmpl_chaleur")…

P.S. I use clone because there are several files of same structure which needs to be added as AddFriend(). To not confuse between ‘friends’ I take original TChain and at each iteration add only one friend…

4

Hi,

Is any of the GetMaximum values ‘correct’ (i.e. same as what the Draw claims)? Can you send an example reproducing the problem?

Cheers,
Philippe.

5

The value of

calibNtps->GetMaximum("WienerAmpl_chaleur");

correspond to what I see from the plots. For the code, please, see the attachment.
tchain_ttree.C (2.58 KB)

6

Hi,

What is the output of running this scripts? Can you send me also the data file and header files so that I can reproduce the problem?

Thanks,
Philippe.