rf706_histpdf.C

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/// \file
/// \ingroup tutorial_roofit
/// \notebook -js
/// Special p.d.f.'s: histogram-based p.d.f.s and functions
///
/// \macro_image
/// \macro_output
/// \macro_code
/// \author 07/2008 - Wouter Verkerke

#include "RooRealVar.h"
#include "RooDataSet.h"
#include "RooGaussian.h"
#include "RooConstVar.h"
#include "RooPolynomial.h"
#include "RooHistPdf.h"
#include "TCanvas.h"
#include "TAxis.h"
#include "RooPlot.h"
using namespace RooFit;

void rf706_histpdf()
{
   // C r e a t e   p d f   f o r   s a m p l i n g
   // ---------------------------------------------

   RooRealVar x("x", "x", 0, 20);
   RooPolynomial p("p", "p", x, RooArgList(RooConst(0.01), RooConst(-0.01), RooConst(0.0004)));

   // C r e a t e   l o w   s t a t s   h i s t o g r a m
   // ---------------------------------------------------

   // Sample 500 events from p
   x.setBins(20);
   RooDataSet *data1 = p.generate(x, 500);

   // Create a binned dataset with 20 bins and 500 events
   RooDataHist *hist1 = data1->binnedClone();

   // Represent data in dh as pdf in x
   RooHistPdf histpdf1("histpdf1", "histpdf1", x, *hist1, 0);

   // Plot unbinned data and histogram pdf overlaid
   RooPlot *frame1 = x.frame(Title("Low statistics histogram pdf"), Bins(100));
   data1->plotOn(frame1);
   histpdf1.plotOn(frame1);

   // C r e a t e   h i g h   s t a t s   h i s t o g r a m
   // -----------------------------------------------------

   // Sample 100000 events from p
   x.setBins(10);
   RooDataSet *data2 = p.generate(x, 100000);

   // Create a binned dataset with 10 bins and 100K events
   RooDataHist *hist2 = data2->binnedClone();

   // Represent data in dh as pdf in x, apply 2nd order interpolation
   RooHistPdf histpdf2("histpdf2", "histpdf2", x, *hist2, 2);

   // Plot unbinned data and histogram pdf overlaid
   RooPlot *frame2 = x.frame(Title("High stats histogram pdf with interpolation"), Bins(100));
   data2->plotOn(frame2);
   histpdf2.plotOn(frame2);

   TCanvas *c = new TCanvas("rf706_histpdf", "rf706_histpdf", 800, 400);
   c->Divide(2);
   c->cd(1);
   gPad->SetLeftMargin(0.15);
   frame1->GetYaxis()->SetTitleOffset(1.4);
   frame1->Draw();
   c->cd(2);
   gPad->SetLeftMargin(0.15);
   frame2->GetYaxis()->SetTitleOffset(1.8);
   frame2->Draw();
}