gendata.C

#ifndef __CINT__
#include "RooGlobalFunc.h"
#endif
#include "RooAddPdf.h"
#include "RooChebychev.h"
#include "RooDataSet.h"
#include "RooExtendPdf.h"
#include "RooGaussian.h"
#include "RooPlot.h"
#include "RooRealVar.h"
#include "TAxis.h"
#include "TCanvas.h"

using namespace RooFit;

void gendata(int numevents, const char *outfilename) {
  // Declare observable x
  RooRealVar x("x", "x", 0, 10);

  // Create two Gaussian PDFs g1(x,mean1,sigma) anf g2(x,mean2,sigma) and their
  // parameters
  RooRealVar mean("mean", "mean of gaussians", 5);
  RooRealVar sigma1("sigma1", "width of gaussians", 0.5);
  // RooRealVar sigma2("sigma2","width of gaussians",1) ;

  RooGaussian sig1("sig1", "Signal component 1", x, mean, sigma1);
  // RooGaussian sig2("sig2","Signal component 2",x,mean,sigma2) ;

  // Build Chebychev polynomial p.d.f.
  RooRealVar a0("a0", "a0", 0.5, 0., 1.);
  RooRealVar a1("a1", "a1", -0.2, 0., 1.);
  RooChebychev bkg("bkg", "Background", x, RooArgSet(a0, a1));

  // Sum the signal components into a composite signal p.d.f.
  RooRealVar sig1frac("sig1frac", "fraction of component 1 in signal", 0.8, 0.,
                      1.);
  // RooAddPdf sig("sig","Signal",RooArgList(sig1,sig2),sig1frac) ;
  RooAddPdf sig("sig", "Signal", RooArgList(sig1), sig1frac);

  // Sum the composite signal and background into an extended pdf
  // nsig*sig+nbkg*bkg
  RooRealVar nsig("nsig", "number of signal events", 500, 0., 10000);
  RooRealVar nbkg("nbkg", "number of background events", 500, 0, 10000);
  RooAddPdf model("model", "(g1+g2)+a", RooArgList(bkg, sig),
                  RooArgList(nbkg, nsig));

  RooDataSet *data = model.generate(x, numevents);

  // Create a new workspace
  RooWorkspace *w = new RooWorkspace("w", "workspace");
  w->import(model);
  w->import(*data);

  // Print workspace contents
  w->Print();
  // Save the workspace into a ROOT file
  w->writeToFile(outfilename);
  // Workspace will remain in memory after macro finishes
  gDirectory->Add(w);
}