using namespace RooFit ;

void ex6()
{
  // Make model

  // A workspace is a container class for RooFit data modeling objects
  // (variables, functions, probability density functions etc...)
  // Here we make an empty workspace

  RooWorkspace w("w") ;

  // Now we use the 'factory' to fill the workspace with the definition
  // of three variables (x,mean and sigma) and the definition of a Gaussian
  // probability density function 'g' in terms of (x,mean,sigma)s

  w.factory("Exponential::decay(t[0,20],expr::alpha('-1/tau',tau[1.54,0.1,20]))") ;


  RooDataSet* data = w.pdf("decay")->generate(*w.var("t"),100) ;


  RooFitResult* r = w.pdf("decay")->fitTo(*data,Save()) ;
  
  
  RooPlot* frame = w.var("t")->frame() ;
  data->plotOn(frame) ;
  w.pdf("decay")->plotOn(frame) ;
  frame->Draw() ;  
  
  // BLOCK 1
  for (Int_t i=0 ; i<data->numEntries() ; i++){
    Double_t t = data->get(i)->getRealValue("t") ;
    cout << "t[" << i << "] = " << t << endl ;
  }

  
}