rf314_paramfitrange.C

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/// \file
/// \ingroup tutorial_roofit
/// \notebook -js
/// Multidimensional models: working with parametrized ranges in a fit.
///
/// This an example of a fit with an acceptance that changes per-event
///
///   pdf = exp(-t/tau) with t[tmin,5]
///
/// where t and tmin are both observables in the dataset
///
/// \macro_image
/// \macro_output
/// \macro_code
/// \author 07/2008 - Wouter Verkerke

#include "RooRealVar.h"
#include "RooDataSet.h"
#include "RooGaussian.h"
#include "RooConstVar.h"
#include "RooExponential.h"
#include "TCanvas.h"
#include "TAxis.h"
#include "RooPlot.h"
#include "RooFitResult.h"

using namespace RooFit;

void rf314_paramfitrange()
{

   // D e f i n e   o b s e r v a b l e s   a n d   d e c a y   p d f
   // ---------------------------------------------------------------

   // Declare observables
   RooRealVar t("t", "t", 0, 5);
   RooRealVar tmin("tmin", "tmin", 0, 0, 5);

   // Make parametrized range in t : [tmin,5]
   t.setRange(tmin, RooConst(t.getMax()));

   // Make pdf
   RooRealVar tau("tau", "tau", -1.54, -10, -0.1);
   RooExponential model("model", "model", t, tau);

   // C r e a t e   i n p u t   d a t a
   // ------------------------------------

   // Generate complete dataset without acceptance cuts (for reference)
   RooDataSet *dall = model.generate(t, 10000);

   // Generate a (fake) prototype dataset for acceptance limit values
   RooDataSet *tmp = RooGaussian("gmin", "gmin", tmin, RooConst(0), RooConst(0.5)).generate(tmin, 5000);

   // Generate dataset with t values that observe (t>tmin)
   RooDataSet *dacc = model.generate(t, ProtoData(*tmp));

   // F i t   p d f   t o   d a t a   i n   a c c e p t a n c e   r e g i o n
   // -----------------------------------------------------------------------

   RooFitResult *r = model.fitTo(*dacc, Save());

   // P l o t   f i t t e d   p d f   o n   f u l l   a n d   a c c e p t e d   d a t a
   // ---------------------------------------------------------------------------------

   // Make plot frame, add datasets and overlay model
   RooPlot *frame = t.frame(Title("Fit to data with per-event acceptance"));
   dall->plotOn(frame, MarkerColor(kRed), LineColor(kRed));
   model.plotOn(frame);
   dacc->plotOn(frame);

   // Print fit results to demonstrate absence of bias
   r->Print("v");

   new TCanvas("rf314_paramranges", "rf314_paramranges", 600, 600);
   gPad->SetLeftMargin(0.15);
   frame->GetYaxis()->SetTitleOffset(1.6);
   frame->Draw();

   return;
}