// Written by Paul Mullen in July 2010
// Produces a histo for the mock online analysis example

void mass_spectrum() {

  TCanvas *canv = new TCanvas("canv", "A Canvas", 800, 600);

  // We generate a random peak position
  gRandom = new TRandom3(0);
  gRandom->SetSeed(0);
  Double_t x = 0.888 + gRandom->Uniform(0.1); // mass of proton
  cout << "Peak position: " << x << endl;

  // Gaussian distribution
  TF1 *myfunc = new TF1("myfunc", "gaus", 0, 3);
  myfunc->SetParameters(1, x, 0.1);
  //myfunc->Draw();

  // Fill distribution
  TH1F *Mp = new TH1F("Mp", "Mass distribution", 100, 0.5, 1.4);
  Mp->SetLineColor(2);
  Mp->FillRandom("myfunc", 100000); // number of counts
  Mp->SetXTitle("m [GeV/c^{2}]");
  Mp->SetYTitle("counts");
  Mp->Draw();

  // We save to a file
  Char_t filename[14];
  Int_t rnum = gRandom->Uniform(999999);
  sprintf(filename, "run%06d.root", rnum);
  TFile *output = new TFile(filename, "RECREATE");
  Mp->Write();
  output->Close();

  cout << "Output saved in " << filename << endl;
}