Hi, I finally simplified my script enought to post it here. It's still not that much clean, sorry, anyway, seems seems to arise on a TH1::Clone when a function is attached to it. Here the script: <<<< File bug104.C void bug104() { TH1 *tp; TF1 fa("fa","gaus",-1,1); fa.SetParameter(0,1); fa.SetParameter(1,0); for (int nb=0;nb<2;nb++) { TH1 *h1; fa.SetParameter(2,nb/10.); if (nb==0) {h1=new TH1F("h1","h1",100,-1.1,1.1);h1->FillRandom("fa");} if (nb==1) {h1=new TH1F("h2","h2",100,-1.1,1.1);h1->FillRandom("fa");} TF1 f1("f1","gaus"); h1->Fit("f1","Q"); if (nb==0)tp=(TH1*)h1->Clone(); TF1 *fb=tp->GetFunction("f1"); cout << fb->GetParameter(2)<<endl; } } >>>> The output from ROOT version 3.00.06 (i386-linux): * Version 3.00/06 12 March 2001 * .root [0] .x bug104.C <TCanvas::MakeDefCanvas>: created default TCanvas with name c1 7.88193e-09 7.88193e-09 The two values printed out are the same. This is expected. But on latest ROOT: * Version 3.01/05 7 June 2001 * root [0] .x bug104.C <TCanvas::MakeDefCanvas>: created default TCanvas with name c1 7.88193e-09 0.0995868 The second value is in fact the fit result for h2! Not h1! What do you think of it ? Yannick
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