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Counts in the number of tracks

Dear All,
Trying to use this command:

[] Double_t integ = dcalphaboard ->Integral();

to find count in the number tracks from a TH2D histogram.
Then I would like to plot a TGraph using this result.

Can someone kindly assist me, please?

Thank you

Do you have a minimum working example (MWE)? It is difficult to understand what your issue is from your description.


Thank you for your respond. Here is one of the .png file, there are many of these histograms that I would like to get Integral then plot a TGraph vs run-number.

Thank you.

Maybe something like this:

  TGraph *g = new TGraph();
  g->SetTitle("number of tracks;run number;dcalphaboard integral");
  Int_t ifirst = 1; // the first run
  Int_t ilast = 79; // the last run
  for (Int_t i = ifirst; i <= ilast; i++) {
    // open the "i"-th ROOT file, retrieve the "dcalphaboard" and then ...
    Double_t integ = dcalphaboard->Integral();
    Double_t runno = i;
    g->SetPoint(g->GetN(), runno, integ); // add the "next" point to the graph
    // ... close the "i"-th ROOT file (deletes "dcalphaboard")

Thank to so much for your response.

I am reading in these histogram from a file of several other different histograms. Then I am trying to calculate all the normalized integrals of these histograms. Then plotting these normalized integral against run number using TGraph and save new histograms to a new file.

From the code below, I have messed up the code some where but not sure where, need some help, please.

i_ntracks = new TGraph();
TCanvas *ac = new TCanvas(“ac”,“ac”,800,600);
while ( runflist >> rootfile )
run = getrun(rootfile);
Double_t n_maxbins;

t_file[n_runs] = new TFile(rootfile,“READ”);
htrig[n_runs] = (TH1*)t_file[n_runs]->Get(“htrig”)
Double_t nevents = htrig[n_runs]->GetBinContent(1);
//trying to go over all the run number
for(int inbins = 1; inbins <= n_maxbins;inbins ++)
for (int iarm=0; iarm<2; iarm++)
for (int iside=0; iside<2; iside++)
name = “h_dcalphaboard”; name += iarm; name += iside;
h_dcalphaboard[n_runs][iarm][iside] = (TH2*)t_file[n_runs]->Get(name);
Double_t intgel = h_dcalphaboard[n_runs][iarm][iside] ->Integral()/htrig[nruns]->GetBinContent(1);//finding the normalized number of tracks
h_dcalphaboard[n_runs][iarm][iside]->Fill( intgel, n_runs );//fill histogram with intgel and run number
//print intgel and Tgraph
TGraph * f = new TGraph;

TFile *savefile = new TFile(“dcalpha.root”,“RECREATE”);//save to file