How to compare histograms from two different ROOT files in which histograms are saved

• Example macro: displayTwofiles.C
• To use this macro, within ROOT do the following

      .L displayTwofiles.C
      displayTwofiles( .....) // depending on your file names, histogram names, etc.
    

How to compare histograms from two different ROOT files in which trees are saved

• Example macro: displayTwoTrees.C

How to use ROOT and plot distributions saved in the ROOT file

• Log on to grid03 either via ssh in Linux or putty + xming in Windows

      ssh 140.115.32.53 -l "your_user_id"
    

• If ROOT is not yet setup in your directory, follow the instruction below
  • Check which shell you are running

            echo $SHELL
           

  • If it is tcsh or csh, follow the instruction below.

     
             source /opt/exp_soft/cms/cmsset_default.csh
             cd
             cmsrel CMSSW_3_9_7
             cd CMSSW_3_9_7/src
             cmsenv
            

    * If it is bash, follow the instruction below.

             source /opt/exp_soft/cms/cmsset_default.sh
             cd
             cmsrel CMSSW_3_9_7
             cd CMSSW_3_9_7/src
             cmsenv
            

• Create a directory in your home area

       cd
       mkdir rootExercise
       cd rootExercise
     

• Copy the following files to this directory

     cp -p /data/syu/Plot_jiechen.* .
    

• Check if the files are there

     ls
    

• Enter ROOT and run the macro

      root -l
      .L Plot_jiechen.C++
      Plot_jiechen a;
      a.Loop();
     

• The test root file is big. Therefore, it will take about 5 mins to finish.
• Then, exit ROOT

      .q
     

• An output file "output_histo.root" will be created in the same directory. You could open the root file to see the content.

       root -l output_histo.root
       .ls
       h_phoet->Draw();
       h_phophi->Draw();
       

• Please modify Plot_jiechen.C to make histograms for other photon variables (pho*...).

How to write a macro for any ROOT file format

• Here is the macro:
• To use the example macro:

     .L loopEntries.C++
     loopEntries()
    

• Caveat!!! You need to declare the variables you want to use with the correct data type.
  For example, if I want to take the variable "phoEt" and the variable is saved as a Double_t. When assigning a local variable to phoEt, I can't use Float_t

How to create macro for any ROOT file format with MakeClass

• Supposedly if your ROOT file is /data/syu/31x_7TeV_PhotonJet_Pt15_pythia.root

       root -l /data/syu/31x_7TeV_PhotonJet_Pt15_pythia.root
    

• You need to know the name of the tree saved in this ROOT file, use TBrowser to find the name. In this example, the name of TTree is EventTree.

     EventTree->MakeClass("myMacro");
    

  You could change myMacro to any name you prefer.
• Now two files are created, myMacro.h and myMacro.C.
• You could modify these two files to do your analysis.

-- ShinShanYu - 24-Apr-2011