// Plot one or more histograms in a single histogram as a single canvas.

void write_hist()
{
  TH1F *his = new TH1F("his", "", 10000, 0., 1.0E9);
  his->GetXaxis()->SetTitle("Energy (GeV)");
  his->GetYaxis()->SetTitle("Counts");
  
  TFile *f1 = TFile::Open("muon_energy.root", "READ");
  TH1F *h1 = (TH1F*)f1->Get("hs");
  h1->SetLineColor(kRed);
  his->Add(h1);
  
  TFile *f2 = TFile::Open("meson_energy.root", "READ");
  TH1F *h2 = (TH1F*)f2->Get("hs");
  h2->SetLineColor(kBlue);
  his->Add(h2);
  
  TFile *fout = new TFile("energy_hist.root", "RECREATE");
  his->Write();
  fout->Close();
  
  
 }