rf804_mcstudy_constr.C File Reference

Detailed Description

'VALIDATION AND MC STUDIES' RooFit tutorial macro #804

Using RooMCStudy on models with constrains

Processing /mnt/build/workspace/root-makedoc-v608/rootspi/rdoc/src/v6-08-00-patches/tutorials/roofit/rf804_mcstudy_constr.C...

#include "RooRealVar.h"
#include "RooDataSet.h"
#include "RooGaussian.h"
#include "RooConstVar.h"
#include "RooPolynomial.h"
#include "RooAddPdf.h"
#include "RooProdPdf.h"
#include "RooMCStudy.h"
#include "RooPlot.h"
#include "TCanvas.h"
#include "TAxis.h"
#include "TH1.h"
using namespace RooFit ;


void rf804_mcstudy_constr()
{
   // C r e a t e   m o d e l   w i t h   p a r a m e t e r   c o n s t r a i n t
   // ---------------------------------------------------------------------------

   // Observable
   RooRealVar x("x","x",-10,10) ;

   // Signal component
   RooRealVar m("m","m",0,-10,10) ;
   RooRealVar s("s","s",2,0.1,10) ;
   RooGaussian g("g","g",x,m,s) ;

   // Background component
   RooPolynomial p("p","p",x) ;

   // Composite model
   RooRealVar f("f","f",0.4,0.,1.) ;
   RooAddPdf sum("sum","sum",RooArgSet(g,p),f) ;

   // Construct constraint on parameter f
   RooGaussian fconstraint("fconstraint","fconstraint",f,RooConst(0.7),RooConst(0.1)) ;

   // Multiply constraint with p.d.f
   RooProdPdf sumc("sumc","sum with constraint",RooArgSet(sum,fconstraint)) ;



   // S e t u p   t o y   s t u d y   w i t h   m o d e l
   // ---------------------------------------------------

   // Perform toy study with internal constraint on f
   RooMCStudy mcs(sumc,x,Constrain(f),Silence(),Binned(),FitOptions(PrintLevel(-1))) ;

   // Run 500 toys of 2000 events.  
   // Before each toy is generated, a value for the f is sampled from the constraint pdf and 
   // that value is used for the generation of that toy.
   mcs.generateAndFit(500,2000) ;

   // Make plot of distribution of generated value of f parameter
   TH1* h_f_gen = mcs.fitParDataSet().createHistogram("f_gen",-40) ;

   // Make plot of distribution of fitted value of f parameter
   RooPlot* frame1  = mcs.plotParam(f,Bins(40)) ;
   frame1->SetTitle("Distribution of fitted f values") ;

   // Make plot of pull distribution on f
   RooPlot* frame2 = mcs.plotPull(f,Bins(40),FitGauss()) ;
   frame1->SetTitle("Distribution of f pull values") ;



   TCanvas* c = new TCanvas("rf804_mcstudy_constr","rf804_mcstudy_constr",1200,400) ;
   c->Divide(3) ;
   c->cd(1) ; gPad->SetLeftMargin(0.15) ; h_f_gen->GetYaxis()->SetTitleOffset(1.4) ; h_f_gen->Draw() ;
   c->cd(2) ; gPad->SetLeftMargin(0.15) ; frame1->GetYaxis()->SetTitleOffset(1.4) ; frame1->Draw() ;
   c->cd(3) ; gPad->SetLeftMargin(0.15) ; frame2->GetYaxis()->SetTitleOffset(1.4) ; frame2->Draw() ;

}

Author

07/2008 - Wouter Verkerke

Definition in file rf804_mcstudy_constr.C.