rf604_constraints.C

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/// \file
/// \ingroup tutorial_roofit
/// \notebook -nodraw
///  'LIKELIHOOD AND MINIMIZATION' RooFit tutorial macro #604
///
///  Fitting with constraints
///
/// \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 "RooAddPdf.h"
#include "RooProdPdf.h"
#include "RooFitResult.h"
#include "RooPlot.h"
#include "TCanvas.h"
#include "TAxis.h"
#include "TH1.h"
using namespace RooFit ;


void rf604_constraints()
{

   // C r e a t e   m o d e l  a n d   d a t a s e t 
   // ----------------------------------------------

   // Construct a Gaussian p.d.f
   RooRealVar x("x","x",-10,10) ;

   RooRealVar m("m","m",0,-10,10) ;
   RooRealVar s("s","s",2,0.1,10) ;
   RooGaussian gauss("gauss","gauss(x,m,s)",x,m,s) ;

   // Construct a flat p.d.f (polynomial of 0th order)
   RooPolynomial poly("poly","poly(x)",x) ;

   // Construct model = f*gauss + (1-f)*poly
   RooRealVar f("f","f",0.5,0.,1.) ;
   RooAddPdf model("model","model",RooArgSet(gauss,poly),f) ;

   // Generate small dataset for use in fitting below
   RooDataSet* d = model.generate(x,50) ;



   // C r e a t e   c o n s t r a i n t   p d f 
   // -----------------------------------------

   // Construct Gaussian constraint p.d.f on parameter f at 0.8 with resolution of 0.1
   RooGaussian fconstraint("fconstraint","fconstraint",f,RooConst(0.8),RooConst(0.1)) ;



   // M E T H O D   1   -   A d d   i n t e r n a l   c o n s t r a i n t   t o   m o d e l 
   // -------------------------------------------------------------------------------------

   // Multiply constraint term with regular p.d.f using RooProdPdf
   // Specify in fitTo() that internal constraints on parameter f should be used

   // Multiply constraint with p.d.f
   RooProdPdf modelc("modelc","model with constraint",RooArgSet(model,fconstraint)) ;
   
   // Fit model (without use of constraint term)
   RooFitResult* r1 = model.fitTo(*d,Save()) ;

   // Fit modelc with constraint term on parameter f
   RooFitResult* r2 = modelc.fitTo(*d,Constrain(f),Save()) ;



   // M E T H O D   2   -     S p e c i f y   e x t e r n a l   c o n s t r a i n t   w h e n   f i t t i n g
   // -------------------------------------------------------------------------------------------------------

   // Construct another Gaussian constraint p.d.f on parameter f at 0.8 with resolution of 0.1
   RooGaussian fconstext("fconstext","fconstext",f,RooConst(0.2),RooConst(0.1)) ;

   // Fit with external constraint
   RooFitResult* r3 = model.fitTo(*d,ExternalConstraints(fconstext),Save()) ;



   // Print the fit results
   cout << "fit result without constraint (data generated at f=0.5)" << endl ;
   r1->Print("v") ;
   cout << "fit result with internal constraint (data generated at f=0.5, constraint is f=0.8+/-0.2)" << endl ;
   r2->Print("v") ;
   cout << "fit result with (another) external constraint (data generated at f=0.5, constraint is f=0.2+/-0.1)" << endl ;
   r3->Print("v") ;
  
}