rf602_chi2fit.C: 'LIKELIHOOD AND MINIMIZATION' RooFit tutorial macro #602
//////////////////////////////////////////////////////////////////////////
//
// 'LIKELIHOOD AND MINIMIZATION' RooFit tutorial macro #602
//
// Setting up a binning chi^2 fit
//
//
//
// 07/2008 - Wouter Verkerke
//
/////////////////////////////////////////////////////////////////////////
#ifndef __CINT__
#include "RooGlobalFunc.h"
#endif
#include "RooRealVar.h"
#include "RooDataSet.h"
#include "RooGaussian.h"
#include "RooChebychev.h"
#include "RooAddPdf.h"
#include "RooChi2Var.h"
#include "RooMinuit.h"
#include "TCanvas.h"
#include "RooPlot.h"
using namespace RooFit ;
void rf602_chi2fit()
{
// S e t u p m o d e l
// ---------------------
// Declare observable x
RooRealVar x("x","x",0,10) ;
// Create two Gaussian PDFs g1(x,mean1,sigma) anf g2(x,mean2,sigma) and their paramaters
RooRealVar mean("mean","mean of gaussians",5) ;
RooRealVar sigma1("sigma1","width of gaussians",0.5) ;
RooRealVar sigma2("sigma2","width of gaussians",1) ;
RooGaussian sig1("sig1","Signal component 1",x,mean,sigma1) ;
RooGaussian sig2("sig2","Signal component 2",x,mean,sigma2) ;
// Build Chebychev polynomial p.d.f.
RooRealVar a0("a0","a0",0.5,0.,1.) ;
RooRealVar a1("a1","a1",-0.2,0.,1.) ;
RooChebychev bkg("bkg","Background",x,RooArgSet(a0,a1)) ;
// Sum the signal components into a composite signal p.d.f.
RooRealVar sig1frac("sig1frac","fraction of component 1 in signal",0.8,0.,1.) ;
RooAddPdf sig("sig","Signal",RooArgList(sig1,sig2),sig1frac) ;
// Sum the composite signal and background
RooRealVar bkgfrac("bkgfrac","fraction of background",0.5,0.,1.) ;
RooAddPdf model("model","g1+g2+a",RooArgList(bkg,sig),bkgfrac) ;
// C r e a t e b i n n e d d a t a s e t
// -----------------------------------------
RooDataSet* d = model.generate(x,10000) ;
RooDataHist* dh = d->binnedClone() ;
// Construct a chi^2 of the data and the model,
// which is the input probability density scaled
// by the number of events in the dataset
RooChi2Var chi2("chi2","chi2",model,*dh) ;
// Use RooMinuit interface to minimize chi^2
RooMinuit m(chi2) ;
m.migrad() ;
m.hesse() ;
// Note that entries with zero bins are _not_ allowed
// for a proper chi^2 calculation and will give error
// messages
RooDataSet* dsmall = (RooDataSet*) d->reduce(EventRange(1,100)) ;
RooDataHist* dhsmall = dsmall->binnedClone() ;
RooChi2Var chi2_lowstat("chi2_lowstat","chi2",model,*dhsmall) ;
cout << chi2_lowstat.getVal() << endl ;
}
Last change: Wed Dec 17 10:56:34 2008
Last generated: 2008-12-17 10:56
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