doc/v606/rf604__constraints_8C.html

#ifndef __CINT__

#include "RooGlobalFunc.h"

#endif

#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") ;


}