Re: [ROOT] trouble using TSelector class

From: Rene Brun (Rene.Brun@cern.ch)
Date: Fri Mar 22 2002 - 15:49:00 MET


Hi Mark,

Why do you do:
 b_had_mass->GetEntry(23);

it should be:
 b_had_mass->GetEntry(entry);

Rene Brun

Mark Hodgkinson wrote:
> 
> I am using  the skeleton produced by TTree::MakeSelector to analyse some
>  MC from the kk generator. When I look at a certain branch from a tree
> using both this (with no cuts added) and also by looking at it directly
> using TBrowser (also with no cuts) I get totally different histograms. The Selector
> method shows one sharp spike, whereas the TBRowser shows the correct broad
> distribution (I have seen many examples of the plot being a broad
> distribution rather than one spike). Here is the code I used in the
> skeleton:
>  #define mark2_cxx
>  #include "mark2.h"
>  #include "TH2.h"
>  #include "TStyle.h"
>  #include "TCanvas.h"
>  void mark2::Begin(TTree *tree)
>  {
> 
>  Init(tree);
>  TString option = GetOption();
> 
>  gDirectory->Delete("qsquared");
>  qsquared = new TH1F("qsquared", "q squared, tau", 120, 0, 6);
>  }
> 
>  Bool_t mark2::ProcessCut(Int_t entry)
>  {
>  return kTRUE;
>  }
> 
>  void mark2::ProcessFill(Int_t entry)
>  {
>  b_had_mass->GetEntry(23);
>  qsquared->Fill(had_mass);
>  }
> 
>  void mark2::Terminate()
>  {
>  gStyle->SetOptStat(11111);
>  TCanvas *c1 = new TCanvas("c1", "kk2 comparison with koralb", 10, 10,
> 800, 600);
>  c1->SetBottomMargin(0.15);
>  qsquared->GetXaxis()->SetTitle("Invariant Mass of tau");
>  qsquared->GetXaxis()->SetTitleOffset(1.4);
>  qsquared->Draw();
>  }
> 
>  The above code is called mark2.C. In root I then do:
>  .x chain.C
> 
> where chain.C contains:
> 
>   {
> 
>       TChain chain("h5");
>       chain.Add("kk.root");
> 
>     }
> 
>  Finally I run the mark2.C with chain.Process("mark2.C") and get the
> histogram drawn.
> 
>  I also thought I should be able to do:
>  TFile kk("kk.root")
>  h5.Process("mark2.C")
> 
>  where h5 is a TNuple, but this crashes. Is there a way to do this since
>  a chain seems unnecessary if you only have one root file you want to use.
> 
>  I hope someone can spot my mistake.
> 
>  Thanks,
> 
>  Mark.
> 
> --
> --------------------------------------------------------------------------------------------
> Mark Hodgkinson                         phone (+44)(0)161 2754150
> Office 7-11                             email markhod@hep.man.ac.uk
> HEP Group
> Schuster Laboratory
> University of Manchester
> Oxford Road
> Manchester
> England
> 
> http://www.hep.man.ac.uk/~markhod



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