Re: different fit behaviour in ROOT and ROOFIT

Dear Lorenzo,

I still have some differences performing fits to an histogram using ROOT or ROOFIT (see the attached mail thread). The fit is based on a CrystalBall function for the signal and a double exponential to describe the background.
If you are back from holidays, can you please have a look to my code. I attach the .root file and the the two macros to perform the fit with ROOT or ROOFIT.

  Thanks in advance for your help!

    Roberta

Roberta Arnaldi wrote:
> Hi Lorenzo,
>
> thanks for your help and for looking into this problem when you'll be
> back!
> I checked, but the range of the function is the same in both cases.
> The root file with the histo was already attached to my first mail,
> but I'm resending it.
>
> Have nice holidays,
>
> Roberta
>
>
>
> Lorenzo Moneta wrote:
>> Hi Roberta,
>> This was a possible difference looking at your code, maybe check also
>> the range of the function in both cases. I can have a look at it, but
>> I am right now in vacation and I could look at it only when I am back
>> in the office in about 10 days. You should send me also the root file
>> with the histograms data so I can run your code,
>> Cheers, Lorenzo
>> On Jul 27, 2011, at 5:52 PM, Roberta Arnaldi wrote:
>>
>>
>>> Hi Lorenzo,
>>>
>>> thanks a lot for the very fast answer!
>>> However, even if I remove from ROOT the option "I", I get even
>>> higher values wrt ROOFIT.
>>>
>>> - ROOT without "I" : CB integral: 2226 +- 189, CB width: 78 MeV
>>> - ROOT with "I": CB integral: 2220 +- 183, CB width: 76 MeV
>>> - ROOFIT: CB integral: 2090 +- 158, CB width: 72 MeV
>>>
>>> So this does not seem to explain the difference...
>>>
>>> Thanks,
>>>
>>> Roberta
>>>
>>>
>>> Lorenzo Moneta wrote:
>>>
>>>> Hi Roberta, You are using in ROOT the option "I", integral of
>>>> function in the bin. I don't think this is supported in RooFit and
>>>> I guess this makes a difference in your case Best Regards
>>>>
>>>> Lorenzo
>>>> On Jul 27, 2011, at 5:28 PM, Roberta Arnaldi wrote:
>>>>
>>>>
>>>>
>>>>> Dear All,
>>>>>
>>>>> I'm fitting an invariant mass spectrum histogram with a sum of
>>>>> functions (Crystal Ball for the peak and two exponentials for the
>>>>> background), using ROOT or ROOTFIT.
>>>>> Initial parameters, fit limits...are the same in both cases.
>>>>>
>>>>> The value I want to extract is the number of signal events under
>>>>> the Crystal Ball (CB) and the width of the Crystal Ball itself.
>>>>> Even if the fit quality is good in both cases, the number of
>>>>> events under the Crystal Ball is systematically different (~6-10%
>>>>> depending on the fit), as well as the CB width. In particular,
>>>>> ROOFIT gives always lower values. As an example:
>>>>>
>>>>> - ROOFIT: CB integral: 2090 +- 158, CB width: 72 MeV
>>>>> - ROOT: CB integral: 2220 +- 183, CB width: 76 MeV
>>>>>
>>>>> Do you have any suggestion? I'm using root v5.28.00d and in ROOT I
>>>>> use the options "LI".
>>>>> I attach to the mail the root file and two macro I use to perform
>>>>> the fit with root or roofit.
>>>>>
>>>>> Best regards and thanks in advance for your help,
>>>>>
>>>>> Roberta
>>>>> #ifndef __CINT__
>>>>> #include "RooGlobalFunc.h"
>>>>> #endif
>>>>> #include "RooRealVar.h"
>>>>> #include "RooDataSet.h"
>>>>> #include "RooGaussian.h"
>>>>> #include "RooExponential.h"
>>>>> #include "RooCBShape.h"
>>>>> #include "RooConstVar.h"
>>>>> #include "RooDataHist.h"
>>>>> #include "RooAddPdf.h"
>>>>> #include "RooWorkspace.h"
>>>>> #include "RooFitResult.h"
>>>>> #include "RooExtendPdf.h"
>>>>> #include "RooPlot.h"
>>>>> #include "TCanvas.h"
>>>>> #include "TAxis.h"
>>>>> #include "TStyle.h"
>>>>> #include "TFile.h"
>>>>> #include "TH1.h"
>>>>> using namespace RooFit ;
>>>>>
>>>>> void TestROOFIT(){
>>>>> gStyle->SetOptTitle(0) ;
>>>>> gStyle->SetOptStat(0) ;
>>>>> gStyle->SetPalette(1) ;
>>>>> gStyle->SetCanvasColor(10) ;
>>>>> gStyle->SetFrameFillColor(10) ;
>>>>>
>>>>> TFile *f = new TFile("Histo.root");
>>>>> TH1D *histo = (TH1D*) f->Get("histo");
>>>>> //------------------------------------
>>>>> // define x range and frame
>>>>> //------------------------------------
>>>>>
>>>>> RooRealVar x("DimuonMass","Mass",1.5,5.,"GeV/c^{2}") ;
>>>>> RooPlot* frame = x.frame(Title("Test Roofit")) ;
>>>>> TCanvas *c1 = new TCanvas("c1","c1",20,20,600,600);
>>>>> gPad->SetLogy(1);
>>>>>
>>>>> //------------------------------------
>>>>> // import histo //------------------------------------
>>>>>
>>>>> RooDataSet *datat; RooDataHist *datah;
>>>>> datah = new RooDataHist("datah","datah",x,Import(*histo));
>>>>> datah->plotOn(frame,Name("datah"),DataError(RooAbsData::SumW2),MarkerColor(kRed),MarkerSize(0.8),XErrorSize(0.));
>>>>> datah->statOn(frame);
>>>>>
>>>>> //------------------------------------
>>>>> // define Crystal Ball
>>>>> //------------------------------------
>>>>> RooRealVar cbmean("cb mean","cb_mean",3.096,3.,3.13);
>>>>> RooRealVar cbsigma("cb sigma","cb_sigma",0.08,0.065,0.11);
>>>>> RooRealVar cbn("cb n","cb_n",3.6,0.1,100.);
>>>>> RooRealVar cbalpha("cb alpha","cb_alpha",1,0.1,10.);
>>>>> RooCBShape cb("cb","cb",x,cbmean,cbsigma,cbalpha,cbn) ;
>>>>>
>>>>> cbalpha.setVal(0.98); cbalpha.setConstant(kTRUE);
>>>>> cbn.setVal(5.2); cbn.setConstant(kTRUE);
>>>>> //----------------------------------------------------
>>>>> // fit expo1 //-----------------------------------------------------
>>>>>
>>>>> RooRealVar alpha1("bck1 alpha","bck1_alpha",-2.282635,-5.,0.) ;
>>>>> RooRealVar nbck1("nbck1","nbck1",500,0.,1e10);
>>>>> RooExponential exp1("exp1","exp1",x,alpha1) ;
>>>>> x.setRange("rangeBck1",1.5,2.7);
>>>>> RooExtendPdf ebck1_step1("ebck1_step1","ebck1_step1",exp1,nbck1);
>>>>> RooAddPdf bck1_step1("bck1_step1","exp
>>>>> bck1",RooArgList(ebck1_step1));
>>>>>
>>>>> //-----------------------------------------------------
>>>>> // fit expo2 //
>>>>> ----------------------------------------------------- RooRealVar
>>>>> alpha2("bck2 alpha","bck2_alpha",-0.559789,-10.,0.) ;
>>>>> RooRealVar nbck2("nbck2","nbck2",500,0.,1e10);
>>>>> RooExponential exp2("exp2","exp2",x,alpha2) ;
>>>>> RooExtendPdf ebck2_step1("ebck2_step1","ebck2_step1",exp2,nbck2);
>>>>> RooAddPdf bck2_step1("bck2_step1","exp
>>>>> bck2",RooArgList(ebck2_step1));
>>>>> x.setRange("rangeBck2",3.5,5.);
>>>>>
>>>>> //------------------------------------ ----------------
>>>>> // define expo1+expo2
>>>>> //----------------------------------------------------- RooAddPdf
>>>>> bck("bck","exp1+exp2",RooArgList(ebck1_step1,ebck2_step1));
>>>>> //------------------------------------
>>>>> // fit with signal+bck
>>>>> //------------------------------------
>>>>>
>>>>> RooRealVar nsig("N.JPsi","nsignal",500,0.,1000000);
>>>>> RooExtendPdf esig("esig","esig",cb,nsig);
>>>>> RooAddPdf
>>>>> sum("sum","bck1+bck2+cb",RooArgList(esig,ebck1_step1,ebck2_step1));
>>>>> RooFitResult* r;
>>>>> x.setRange("fitrange",2.,5.);
>>>>> r = sum.fitTo(*datah,Range("fitrange"),Extended(kTRUE),Save()) ;
>>>>>
>>>>> //------------------------------------
>>>>> // plot
>>>>> //------------------------------------
>>>>> sum.plotOn(frame,Components("cb"),LineColor(kGreen)) ;
>>>>> sum.plotOn(frame,Components("exp1,exp2"),LineColor(kOrange)) ;
>>>>> sum.plotOn(frame,Name("sum"),LineColor(kBlue)) ;
>>>>> sum.paramOn(frame,Parameters(RooArgSet(cbmean,cbsigma,nsig)),Layout(0.6),Format("NELU",AutoPrecision(2)));
>>>>>
>>>>> frame->Draw() ;
>>>>>
>>>>> }
>>>>> <Histo.root>void TestROOT(){
>>>>>
>>>>> gStyle->SetOptStat(0);
>>>>> gStyle->SetOptTitle(0);
>>>>> gStyle->SetCanvasColor(10);
>>>>> gStyle->SetFrameFillColor(10);
>>>>>
>>>>> //----------------------------------------------------
>>>>> // Open file
>>>>> //----------------------------------------------------
>>>>> TFile *f = new TFile("Histo.root");
>>>>> TH1D *histo = (TH1D*) f->Get("histo"); TCanvas *c = new
>>>>> TCanvas("c","c",20,20,600,600);
>>>>> //----------------------------------------------------
>>>>> // Fit the invariant mass spectrum // with a Crystal Ball function
>>>>> + double exponential
>>>>> //----------------------------------------------------
>>>>> Double_t FitMin=2., FitMax=5.; TF1 *functot = new
>>>>> TF1("functot",FuncTot,FitMin,FitMax,9);
>>>>> functot->SetParameter(0,14.425808); // background parameters
>>>>> functot->SetParameter(1,-2.282635); // background parameters
>>>>> functot->SetParameter(2,6.466449); // background parameters
>>>>> functot->SetParameter(3,-0.559789); // background parameters
>>>>> functot->SetParameter(4,2859.295924); // JPsi normalization
>>>>> functot->SetParameter(5,3.130); // JPsi mass position
>>>>> functot->SetParameter(6,0.08); // JPsi width
>>>>> functot->FixParameter(7,0.98); // Crystal Ball tails
>>>>> functot->FixParameter(8,5.2); // Crystal Ball tails
>>>>> functot->SetLineColor(kBlue);
>>>>> functot->SetLineWidth(2);
>>>>>
>>>>> TFitResultPtr r = histo->Fit(functot,"RIlS");
>>>>>
>>>>> TMatrixDSym cov = r->GetCovarianceMatrix();
>>>>> Double_t *fullmat;
>>>>> fullmat = cov.GetMatrixArray();
>>>>> Double_t psimat[25];
>>>>> for(Int_t i=0;i<5;i++){
>>>>> for(Int_t j=0;j<5;j++) psimat[5*i+j]=fullmat[40+j+9*i];
>>>>> }
>>>>>
>>>>> histo->GetXaxis()->SetRangeUser(2.,5.);
>>>>> histo->SetMinimum(1.);
>>>>> gPad->SetLogy(1);
>>>>> histo->Draw("e");
>>>>> histo->SetMarkerStyle(20);
>>>>> histo->SetMarkerColor(2);
>>>>> histo->SetMarkerSize(0.7);
>>>>>
>>>>> TF1 *psifix = new TF1("psifix",FuncJpsi,0.,5.,9); for(int
>>>>> i=0;i<9;i++) psifix->SetParameter(i,functot->GetParameter(i));
>>>>> psifix->SetLineColor(kGreen);
>>>>> psifix->Draw("same");
>>>>> Double_t binWidth= histo->GetBinWidth(1);
>>>>> Double_t NPsi=psifix->Integral(0.,5.)/binWidth;
>>>>>
>>>>> TF1 *psifix2 = new TF1("psifix2",FuncJpsi2,0.,5.,5); for(int
>>>>> i=0;i<5;i++) psifix2->SetParameter(i,functot->GetParameter(i+4));
>>>>> Double_t psipar[5];
>>>>> for(int i=0;i<5;i++) psipar[i]=functot->GetParameter(4+i);
>>>>> Double_t ErrPsiCorrParam =
>>>>> psifix2->IntegralError(0.,5.,psipar,psimat)/binWidth;
>>>>>
>>>>> char text3[100];
>>>>> sprintf(text3,"N_{J/#psi}= %3.0f #pm %2.0f",NPsi,ErrPsiCorrParam);
>>>>> TLatex *l1 = new
>>>>> TLatex(3.35,psifix2->Integral(0.,5.)/binWidth*8/5.,text3);
>>>>> l1->Draw();
>>>>>
>>>>> char text5[100];
>>>>> sprintf(text5,"#sigma_{J/#psi}= %5.3f #pm %5.3f
>>>>> GeV/c^{2}",functot->GetParameter(6),functot->GetParError(6));
>>>>> TLatex *l3 = new
>>>>> TLatex(3.35,psifix2->Integral(0.,5.)/binWidth*0.3*5./1.5,text5);
>>>>> l3->SetTextSize(0.035);
>>>>> l3->Draw();
>>>>> }
>>>>>
>>>>> Double_t FuncJpsi(Double_t *x, Double_t *par){ //Crystal Ball
>>>>> Double_t FitJPsi;
>>>>> Double_t t = (x[0]-par[5])/par[6];
>>>>> if (t > (-par[7])){
>>>>> FitJPsi = par[4]*TMath::Exp(-t*t/2.);
>>>>> } else if (t <= (-par[7])) {
>>>>> Double_t AA =
>>>>> TMath::Power(par[8]/TMath::Abs(par[7]),par[8])*TMath::Exp(-TMath::Abs(par[7])*TMath::Abs(par[7])/2.);
>>>>>
>>>>> Double_t BB = par[8]/TMath::Abs(par[7])-TMath::Abs(par[7]);
>>>>> if(TMath::Power((BB-t),par[8])!=0){
>>>>> FitJPsi = par[4]*AA/TMath::Power((BB-t),par[8]);
>>>>> } else FitJPsi = 0;
>>>>> } return FitJPsi;
>>>>> }
>>>>>
>>>>> Double_t FuncJpsi2(Double_t *x, Double_t *par){ //Crystal Ball
>>>>> Double_t FitJPsi;
>>>>> Double_t t = (x[0]-par[1])/par[2];
>>>>> if (t > (-par[3])){
>>>>> FitJPsi = par[0]*TMath::Exp(-t*t/2.);
>>>>> } else if (t <= (-par[3])) {
>>>>> Double_t AA =
>>>>> TMath::Power(par[4]/TMath::Abs(par[3]),par[4])*TMath::Exp(-TMath::Abs(par[3])*TMath::Abs(par[3])/2.);
>>>>>
>>>>> Double_t BB = par[4]/TMath::Abs(par[3])-TMath::Abs(par[3]);
>>>>> if(TMath::Power((BB-t),par[4])!=0){
>>>>> FitJPsi = par[0]*AA/TMath::Power((BB-t),par[4]);
>>>>> } else FitJPsi = 0;
>>>>> } return FitJPsi;
>>>>> }
>>>>>
>>>>> Double_t FuncBck1(Double_t *x, Double_t *par){ //exponential
>>>>> Double_t FitBck1 = exp(par[0]+par[1]*x[0]);
>>>>> return FitBck1;
>>>>> }
>>>>> Double_t FuncBck2(Double_t *x, Double_t *par){ //exponential
>>>>> Double_t FitBck2 = exp(par[2]+par[3]*x[0]);
>>>>> return FitBck2;
>>>>> }
>>>>>
>>>>> Double_t FuncBck(Double_t *x, Double_t *par){ //exponential
>>>>> return FuncBck1(x,par)+FuncBck2(x,par);
>>>>> }
>>>>>
>>>>> Double_t FuncTot(Double_t *x, Double_t *par){ // total fit
>>>>> return FuncBck(x,par)+FuncJpsi(x,par);
>>>>> }
>>>>>
>>>>
>>>>
>>
>>