ROOT   6.21/01 Reference Guide
h1analysisProxy.C File Reference

## Detailed Description

Example of analysis class for the H1 data using code generated by MakeProxy.

This file uses 4 large data sets from the H1 collaboration at DESY Hamburg. One can access these data sets (277 MBytes) from the standard Root web site at: ftp:///root.cern.ch/root/h1analysis The Physics plots below generated by this example cannot be produced when using smaller data sets.

There are several ways to analyze data stored in a Root Tree

• Using TTree::Draw: This is very convenient and efficient for small tasks. A TTree::Draw call produces one histogram at the time. The histogram is automatically generated. The selection expression may be specified in the command line.
• Using the TTreeViewer: This is a graphical interface to TTree::Draw with the same functionality.
• Using the code generated by TTree::MakeClass: In this case, the user creates an instance of the analysis class. They have the control over the event loop and he can generate an unlimited number of histograms.
• Using the code generated by TTree::MakeSelector. Like for the code generated by TTree::MakeClass, the user can do complex analysis. However, they cannot control the event loop. The event loop is controlled by TTree::Process called by the user. This solution is illustrated by the current code. The advantage of this method is that it can be run in a parallel environment using PROOF (the Parallel Root Facility).

A chain of 4 files (originally converted from PAW ntuples) is used to illustrate the various ways to loop on Root data sets. Each data set contains a Root Tree named "h42"

h1analysProxy.C can be used either via TTree::Draw:

h42->Draw("h1analysisProxy.C");

or it can be used directly with TTree::MakeProxy, for example to generate a shared library. TTree::MakeProxy will generate a TSelector skeleton that include h1analysProxy.C:

h42->MakeProxy("h1sel","h1analysisProxy.C");

This produces one file: h1sel.h which does a #include "h1analysProxy.C" The h1sel class is derived from the Root class TSelector and can then be used as:

h42->Process("h1sel.h+");

The following members functions are called by the TTree::Process functions.

• h1analysProxy_Begin(): Called every time a loop on the tree starts. a convenient place to create your histograms.
• h1analysProxy_Notify(): This function is called at the first entry of a new Tree in a chain.
• h1analysProxy_Process(): called to analyze each entry.
• h1analysProxy_Terminate(): called at the end of a loop on a TTree. a convenient place to draw/fit your histograms.

To use this file, try the following session

Root > gROOT->Time(); ///will show RT & CPU time per command

### Case A: Create a TChain with the 4 H1 data files

The chain can be created by executed the short macro h1chain.C below:

{
TChain chain("h42");
chain.Add("$H1/dstarmb.root"); /// 21330730 bytes 21920 events chain.Add("$H1/dstarp1a.root"); /// 71464503 bytes 73243 events
chain.Add("$H1/dstarp1b.root"); /// 83827959 bytes 85597 events chain.Add("$H1/dstarp2.root"); /// 100675234 bytes 103053 events
///where \$H1 is a system symbol pointing to the H1 data directory.
}

### Case B: Loop on all events

Root > chain.Draw("h1analysisProxy.C")

### Case C: Same as B, but in addition fill the event list with selected entries.

The event list is saved to a file "elist.root" by the Terminate function. To see the list of selected events, you can do elist->Print("all"). The selection function has selected 7525 events out of the 283813 events in the chain of files. (2.65 per cent)

Root > chain.Draw("h1analysisProxy.C","","fillList")

### Case D: Process only entries in the event list

The event list is read from the file in elist.root generated by step C

Root > chain.Draw("h1analysisProxy.C","","useList")

The commands executed with the 3 different methods B,C and D produce two canvases shown below: begin_html the Dstar plot end_html begin_html the Tau D0 plot end_html

TEntryList *elist;
Bool_t useList, fillList;
TH1F *hdmd;
TH2F *h2;
void h1analysisProxy_Begin(TTree *tree)
{
// function called before starting the event loop
// -it performs some cleanup
// -it creates histograms
// -it sets some initialisation for the event list
//print the option specified in the Process function.
TString option = GetOption();
printf("Starting (begin) h1analysis with process option: %s\n",option.Data());
//process cases with event list
fillList = kFALSE;
useList = kFALSE;
if (fChain) fChain->SetEntryList(0);
delete gDirectory->GetList()->FindObject("elist");
// case when one creates/fills the event list
if (option.Contains("fillList")) {
fillList = kTRUE;
elist = new TEntryList("elist","H1 selection from Cut");
// Add to the input list for processing in PROOF, if needed
if (fInput) {
}
} else elist = 0;
// case when one uses the event list generated in a previous call
if (option.Contains("useList")) {
useList = kTRUE;
if (fInput) {
tree->SetEntryList(elist);
TFile f("elist.root");
elist = (TEntryList*)f.Get("elist");
if (elist) elist->SetDirectory(0); //otherwise the file destructor will delete elist
} else {
// Option "useList" not supported in PROOF directly
Warning("Begin", "option 'useList' not supported in PROOF - ignoring");
Warning("Begin", "the entry list must be set on the chain *before* calling Process");
}
}
}
void h1analysisProxy_SlaveBegin(TTree *tree)
{
// function called before starting the event loop
// -it performs some cleanup
// -it creates histograms
// -it sets some initialisation for the entry list
//print the option specified in the Process function.
TString option = GetOption();
printf("Starting (slave) h1analysis with process option: %s\n",option.Data());
//create histograms
hdmd = new TH1F("hdmd","dm_d",40,0.13,0.17);
h2 = new TH2F("h2","ptD0 vs dm_d",30,0.135,0.165,30,-3,6);
//process cases with entry list
fillList = kFALSE;
useList = kFALSE;
// case when one creates/fills the entry list
if (option.Contains("fillList")) {
fillList = kTRUE;
// Get the list
if (fInput) {
if ((elist = (TEntryList *) fInput->FindObject("elist")))
// Need to clone to avoid problems when destroying the selector
elist = (TEntryList *) elist->Clone();
}
if (elist)
else
fillList = kFALSE;
} else elist = 0;
// case when one uses the entry list generated in a previous call
if (option.Contains("useList")) {
useList = kTRUE;
TFile f("elist.root");
elist = (TEntryList*)f.Get("elist");
if (elist) elist->SetDirectory(0); //otherwise the file destructor will delete elist
if (tree) tree->SetEntryList(elist);
else {
// Option "useList" not supported in PROOF directly
Warning("Begin", "option 'useList' not supported in PROOF - ignoring");
Warning("Begin", "the entry list must be set on the chain *before* calling Process");
}
}
}
Double_t h1analysisProxy() {
return 0;
}
Bool_t h1analysisProxy_Process(Long64_t entry)
{
// entry is the entry number in the current Tree
// Selection function to select D* and D0.
//in case one entry list is given in input, the selection has already been done.
if (!useList) {
float f1 = md0_d;
float f2 = md0_d-1.8646;
bool test = TMath::Abs(md0_d-1.8646) >= 0.04;
if (gDebug>0) fprintf(stderr,"entry #%lld f1=%f f2=%f test=%d\n",
if (TMath::Abs(md0_d-1.8646) >= 0.04) return kFALSE;
if (ptds_d <= 2.5) return kFALSE;
if (TMath::Abs(etads_d) >= 1.5) return kFALSE;
int cik = ik-1; //original ik used f77 convention starting at 1
int cipi = ipi-1; //original ipi used f77 convention starting at 1
f1 = nhitrp[cik];
f2 = nhitrp[cipi];
test = nhitrp[cik]*nhitrp[cipi] <= 1;
if (gDebug>0) fprintf(stderr,"entry #%lld f1=%f f2=%f test=%d\n",
if (nhitrp[cik]*nhitrp[cipi] <= 1) return kFALSE;
if (rend[cik] -rstart[cik] <= 22) return kFALSE;
if (rend[cipi]-rstart[cipi] <= 22) return kFALSE;
if (nlhk[cik] <= 0.1) return kFALSE;
if (nlhpi[cipi] <= 0.1) return kFALSE;
if (nlhpi[ipis-1] <= 0.1) return kFALSE;
if (njets < 1) return kFALSE;
}
// if option fillList, fill the event list
if (fillList) elist->Enter(entry);
//fill some histograms
hdmd->Fill(dm_d);
h2->Fill(dm_d,rpd0_t/0.029979*1.8646/ptd0_d);
return kTRUE;
}
void h1analysisProxy_SlaveTerminate()
{
// nothing to be done
printf("Terminate (slave) h1analysis\n");
}
void h1analysisProxy_Terminate()
{
printf("Terminate (final) h1analysis\n");
// function called at the end of the event loop
hdmd = dynamic_cast<TH1F*>(fOutput->FindObject("hdmd"));
h2 = dynamic_cast<TH2F*>(fOutput->FindObject("h2"));
if (hdmd == 0 || h2 == 0) {
Error("Terminate", "hdmd = %p , h2 = %p", hdmd, h2);
return;
}
//create the canvas for the h1analysis fit
TCanvas *c1 = new TCanvas("c1","h1analysis analysis",10,10,800,600);
c1->SetBottomMargin(0.15);
hdmd->GetXaxis()->SetTitle("m_{K#pi#pi} - m_{K#pi}[GeV/c^{2}]");
hdmd->GetXaxis()->SetTitleOffset(1.4);
//fit histogram hdmd with function f5 using the log-likelihood option
TF1 *f5 = new TF1("f5",fdm5,0.139,0.17,5);
f5->SetParameters(1000000, .25, 2000, .1454, .001);
hdmd->Fit("f5","lr");
//create the canvas for tau d0
TCanvas *c2 = new TCanvas("c2","tauD0",100,100,800,600);
c2->SetGrid();
c2->SetBottomMargin(0.15);
// Project slices of 2-d histogram h2 along X , then fit each slice
// with function f2 and make a histogram for each fit parameter
// Note that the generated histograms are added to the list of objects
// in the current directory.
TF1 *f2 = new TF1("f2",fdm2,0.139,0.17,2);
f2->SetParameters(10000, 10);
h2->FitSlicesX(f2,0,-1,1,"qln");
TH1D *h2_1 = (TH1D*)gDirectory->Get("h2_1");
h2_1->GetXaxis()->SetTitle("#tau[ps]");
h2_1->SetMarkerStyle(21);
h2_1->Draw();
c2->Update();
TLine *line = new TLine(0,0,0,c2->GetUymax());
line->Draw();
// Have the number of entries on the first histogram (to cross check when running
// with entry lists)
TPaveStats *psdmd = (TPaveStats *)hdmd->GetListOfFunctions()->FindObject("stats");
psdmd->SetOptStat(1110);
c1->Modified();
//save the entry list to a Root file if one was produced
if (fillList) {
elist = dynamic_cast<TEntryList*>(fOutput->FindObject("elist"));
if (elist) {
TFile efile("elist.root","recreate");
elist->Write();
} else {