Dear Rene,
I think "logL += TMath::Log(prob) * weight[i]/sum;" should be
"logL += TMath::Log(prob) * weight[i];".
Don't divide "weight[i]" by "sum". I'm sorry .
This makes difference in the error evaluation of the fit.
I think the fix below is right...
//////////////////////////////////////////////////////////
prob = fitfunc->EvalPar(x,par);
if(prob > 0) logL += TMath::Log(prob) * weight[i];
else logL += logEpsilon * weight[i];
//////////////////////////////////////////////////////////
Best Regards,
Hajime
> Hi Hajime,
>
> Thanks very much for your correction when using the weights.
> iIt clearly improves the fit.
>
> It is now in CVS.
>
> Rene Brun
>
> Hajime Nanjyo wrote:
> >
> > Dear ROOTers,
> >
> > I found a bug in the function TreeUnbinnedFitLikelihood in TTreePlayer.cxx,
> > which was related to a bug in TTree::UnbinnedFit.
> >
> > In the function TreeUnbinnedFitLikelihood, event weights were treated as
> > follows.
> > prob = fitfunc->EvalPar(x,par) * weight[i]/sum;
> >
> > I think it should be
> > prob = TMath::Power(fitfunc->EvalPar(x,par),weight[i]/sum).
> >
> > So I propose to change the original code,
> >
> > prob = fitfunc->EvalPar(x,par) * weight[i]/sum;
> > if(prob > 0) logL += TMath::Log(prob);
> > else logL += logEpsilon;
> >
> > to
> >
> > prob = fitfunc->EvalPar(x,par);
> > if(prob > 0) logL += TMath::Log(prob) * weight[i]/sum;
> > else logL += logEpsilon * weight[i]/sum;
> > .
> >
> > I show a small sample, "test.C" to indicate the problem below.
> >
> > It can be compiled and executed as follows.
> > g++ -o test `root-config --cflags` `root-config --libs` -lMinuit test.C
> > ./test
> >
> > In this code, 20000 events with weights are generated and fitted with two ways.
> > 1. Fill a histogram with the weights and fit it.
> > 2. TTree::UnbinnedFit with weights.
> >
> > The results should be same but not the same currently.
> > I already checked that the fix of the TreeUnbinnedFitLikelihood
> > remedy the problem.
> >
> > The ROOT under /afs/cern.ch/sw/root/v4.00.08/rh73_gcc32/root was used
> > with gcc version 3.2 in Red Hat Linux release 7.3 (Valhalla)
> >
> > Could you treat the problem please.
> >
> > Best Regards,
> > Hajime
> >
> > test.C
> > //////////////////////////////////////////////////////////////
> > #include <iostream>
> > #include <cstdio>
> > #include "TROOT.h"
> > #include "TApplication.h"
> > #include "TFile.h"
> > #include "TTree.h"
> > #include "TCanvas.h"
> > #include "TF1.h"
> > #include "TH1.h"
> >
> > int main(int argc,char** argv)
> > {
> > TApplication theApp("App", &argc, argv);
> > gApplication->Init();
> >
> > //---------------------------------
> > // 1.) generate n0 events following 1+x^2+8/3*a0*x with weight w0.
> > // 2.) generate n1 events following 1+x^2+8/3*a1*x with weight w1.
> > // 3.) fill (n0+n1) events in TTree tr0 in TFile test.root.
> > // 4.) Fill values to the TH1D his with weight.
> > // 5.) Fit the histogram with [0]*(1+x^2+8/3*[1]*x)
> > // 6.) Performe UnbinnedFit with p.d.f of 1+x^2+8/3*[0]*x
> > //---------------------------------
> >
> > int n0=10000;
> > int n1=10000;
> >
> > double a0=0.3;
> > double a1=0.6;
> > double w0=0.4;
> > double w1=0.8;
> > //---------------------------------
> >
> >
> > TFile tf("test.root","RECREATE");
> > TF1 f0("f0","1+x*x+8./3.*[0]*x",-1,1);
> > f0.SetParameter(0,a0);
> > f0.SetNpx(1000);
> > TF1 f1("f1","1+x*x+8./3.*[0]*x",-1,1);
> > f1.SetParameter(0,a1);
> > f1.SetNpx(1000);
> >
> > Double_t value, weight;
> >
> > TTree tr0("tr0","tr0");
> > tr0.Branch("value",&value,"value/D");
> > tr0.Branch("weight",&weight,"weight/D");
> >
> > for(int i=0;i<n0;i++) {
> > value=f0.GetRandom();
> > weight=w0;
> > tr0.Fill();
> > }
> > for(int i=0;i<n1;i++) {
> > value=f1.GetRandom();
> > weight=w1;
> > tr0.Fill();
> > }
> > tr0.Write();
> > tf.Close();
> >
> > //---------------------------------
> >
> > TFile tfi("test.root");
> > TTree* tr;
> > tr = (TTree*)tfi.Get("tr0");
> >
> > TF1 fun("fun","[0]*(1+x*x+8./3.*[1]*x)",-1,1);
> >
> > TH1D his("his","his",40,-1,1);
> > tr->Draw("value>>his","weight");
> > his.Fit("fun","","",-1,1);
> > Double_t A0= fun.GetParameter(1);
> > //his.Draw("E");
> > //gPad->Modified();
> > //gPad->Update();
> > //std::cout << "Hit Return" << std::endl;
> > //std::getchar();
> > //---------------------------------
> >
> > TF1 func("func","1+x*x+8./3.*[0]*x",-1,1);
> > tr->UnbinnedFit("func","value","weight","VEM");
> > Double_t A1= func.GetParameter(0);
> >
> > tfi.Close();
> >
> > std::cout << A0 << "\t" << A1 << std::endl;
> > return 0;
> > }
> > //////////////////////////////////////////////////////////////
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