rf706_histpdf.C

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/// \file
/// \ingroup tutorial_roofit
/// \notebook -js
///  'SPECIAL PDFS' RooFit tutorial macro #706
///
///  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() ;


}