On Wed, 15 Aug 2001, Rene Brun wrote: Thanks Rene. Ilia > Ilia, > You should call Sumw2 for the resulting histogram before making > the operation if you want to have the correct error bars computed. > See documentation of the TH1::Add functions. > If your operand histograms already have Sumw2, this is not necessary. > Example: > { > gROOT->Reset(); > TH1F *h1 = new TH1F("h1","h1",100,-3,3); > Int_t bin = h1->Fill(0,1911); > TH1F *h2 = new TH1F("h2","h2",100,-3,3); > h2->Fill(0,1537.57); > TH1F *h3 = h1->Clone("h3"); > h3->Sumw2(); > h3->Add(h1,h2,1,-1); > printf("Bin conte= %g\n",h3->GetBinContent(bin)); > printf("Bin error= %g\n",h3->GetBinError(bin)); > } > > Rene Brun > > On Wed, 15 Aug 2001, Ilia Ravinovich wrote: > > > Hi Rene, > > > > In my macro I'm doing: > > > > inv_reb_signal_n->Add(inv_reb_real_n,inv_reb_mixed_norm_n,1.,-1.); > > inv_reb_signal_n->Print("all"); > > > > I checked the output for example bin #10: > > > > fSumw[10]=373.426, x=1.145, error=43.7226 > > > > But the error is wrong because: > > > > fSumw[10]=1911, x=1.145 (this is from 'inv_reb_real_n') > > fSumw[10]=1537.57, x=1.145 (this is from 'inv_reb_mixed_norm') > > > > 1911-1537.57=373.43, error=sqrt(1911+1537.57)=58.72 > > > > Am I doing something wrong? > > > > Thanks, > > > > Ilia > > > > ************************************************************************ > > * * > > * Ilia Ravinovich * > > * Department of Particle Physics PPE Division * > > * Weizmann Institute of Science Bld 892, 1D-015 * > > * Rehovot 76100 CERN, 1211 Geneva * > > * ISRAEL Switzerland * > > * * > > * PHONE : 972 8 9343187 41 22 7676437 * > > * FAX : 972 8 9466253 41 22 7677910 * > > * E-mail: Ilia.Ravinovich@weizmann.ac.il Ilia.Ravinovich@cern.ch * > > * * > > ************************************************************************ > > > > ************************************************************************ * * * Ilia Ravinovich * * Department of Particle Physics PPE Division * * Weizmann Institute of Science Bld 892, 1D-015 * * Rehovot 76100 CERN, 1211 Geneva * * ISRAEL Switzerland * * * * PHONE : 972 8 9343187 41 22 7676437 * * FAX : 972 8 9466253 41 22 7677910 * * E-mail: Ilia.Ravinovich@weizmann.ac.il Ilia.Ravinovich@cern.ch * * * ************************************************************************
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