Draw a rebinned histogramm from ascii2root2TTree

ROOT
1

Hello co-rooters!

I would like to divide to histograms that don’t have the same binning(an experimental and an evaluated one)
To do that, I take the evaluated one, which in principle has a finer binning, in ascii format, convert it to a root file and then rebin it in a coarser binning.

My code that converts the ascii file to root file is the following

[code]{
gROOT->Reset();
TFile *f = new TFile(“refXS_tot.root”,“NEW”);

//~~~~~~~~~~~~~~~~~~~~~ 235U ~~~~~~~~~~~~~~~~~~~~~~// 
TTree *TU = new TTree("U235_ENDFtot","data from ascii file");
Long64_t nlines = TU->ReadFile("U5_cross_section_eV.txt","E:XS");
printf("Found %lld points\n",nlines);
TU->Write();

int n = TU->Draw("E:XS");
TGraph *g = new TGraph(nlines,TU->GetV1(),TU->GetV2());
g->Draw("apl");

f->Close();

}[/code]

The code that reads the previously created root file and “tries” to plot a rebinned version of it is the following

[code]{

TFile *MyFile = new TFile("refXS_tot.root","READ");//Open the root file
if ( MyFile->IsOpen() ) printf("File opened successfully\n");//Check if file is opened
TTree *XSTree  = (TTree*)MyFile.Get("U235_ENDFtot");//Get the XS tree
//Define the branches
Float_t E;
Float_t XS;
XSTree->SetBranchAddress("E",&E);
XSTree->SetBranchAddress("XS",&XS);
// Get number of entries
Int_t entries = XSTree->GetEntries();
printf(" Number of entries: %d\n",entries);

// Create neutron energy binning - same as the experimental yield
Int_t     N_BPDEC = 2000;// bins per decade
Int_t     E_MIN = -3;// lower energy limit (log10)
Int_t     E_MAX = 8;// upper energy limit (log10)
Int_t     ndec = E_MAX - E_MIN;//total energy range (log 10)
Int_t     nbins = (Int_t) ndec*N_BPDEC;//total numer of bins
Double_t  ebins[nbins+1];
Double_t  step = (Double_t) ndec / nbins;

for(Int_t i=0; i <= nbins; i++) {
  ebins[i] = (float) pow(10., step * (Double_t) i + E_MIN);
}

//X-Section Histogram
TH1F *hXSU5 = new TH1F("hXSU5","^{235}U Evaluated Cross Section - Rebinned; Neutron energy (eV); Cross Section (barns)",nbins,ebins);
hXSU5->Sumw2();
for (int i=0; i<=entries; i++){//Fill the histogram
  hXSU5->Fill(E,XS);
}
hXSU5->Draw();

}[/code]

The problem is that although both codes run without any error whatsoever, the printed histogram that I get is empty, despite having the correct number of entries.

1280×800

Any idea on why I can’t draw the histogram?
Thank you very much in advance!

2

for (int i=0; i<=entries; i++){ XSTree->GetEntry(i); // read E and XS hXSU5->Fill(E,XS); // fill the histogram }

3

Thank you very much for your help!

My output is the following

1280×800

Any idea on why does it have discontinuity?
Does it have to do with the binning?

4

The “correct” unbinned looks like that

1280×800

5

Your “unbinned” is a TGraph, while the “rebinned” is a TH1F (and apparently your x-bins do not correspond 1:1 to your data points, so some bins are not filled at all and some another are filled multiple times).

6

You are absolutely right, but that was the plan : To change the binning of the “unbinned” in order to fit with the experimental binning.

To draw a graph instead of a histogram, I used the following code

double *x=new double[hXSU5->GetNbinsX()]; double *y=new double[hXSU5->GetNbinsX()]; int N=0; for (int i=0; i<hXSU5->GetNbinsX(); i++){ x[N] = hXSU5-> GetBinCenter(i+1); y[N] = hXSU5-> GetBinContent(i+1); N++; } TGraph *XSection = new TGraph(N,x,y); XSection->Draw("al");

but again there are those discontinuities…