Please send a complete macro. It looks like you are using a TGraphErrors but you do not set the errors errE, Err1 and Err2. Please always specify a mail subject title when you send mails to roottalk. see: http://root.cern.ch/root/roottalk/RoottalkRules.html Rene Brun Venkatesh Kaushik wrote: > > Hi ROOTers, > I have two sets of data points, which I am supposed to fit straights line > to. I try to fit both these with pol1, I observe two things > 1) the chi square / dof value is horrible. > 2) visually, i don't see the fit has done a good job. > > i am not sure what's happening. are there any default fit > strategies/parameters that is messing up my fit? > > here's my code snippet. i have also attached the output of this code. > > /********************************************************************/ > # define Constrain 1 > > // Data points are defined here. > Double_t E[n]={5,10,15,20,50,75,100}, par[3]; > Int_t N[n]={77497,45361,28876,49716,13794,12370}; > > Double_t E_Mean1[n]={125.68,214.17,356.12,496.4,1352.61,2067.54,3068.15}; > Double_t errE_Mean1[n]={1.95,1.7,2.53,2.93,12.08,52.08,52.08}; > > Double_t E_Mean2[n]={118.43,215.47,359.58,500.81,1349.5,2019.48,3052.16}; > Double_t errE_Mean2[n]={0.3,1.97,2.24,2.86,10.78,37.96,47.94}; > > // Define two graphs and error bars. > TGraph *gr=new TGraphErrors(7,E,E_Mean1,errE,Err1); > TGraph *gr1=new TGraphErrors(7,E,E_Mean2,errE,Err2); > > // put them in a multigraph. > TMultiGraph *mg = new TMultiGraph(); > mg->Add(gr); > mg->Add(gr1); > mg->Draw("AP"); > // fit pol1 to both graphs. > gr->Fit("pol1"); > TF1 *fline1=gr->GetFunction("pol1"); > if(Constrain)fline1->SetParameter(0,0); > par[0] = fline1->GetParameter(0); > par[1] = fline1->GetParameter(1); > cout << par[0] << " " << par[1] << endl; > fline1->SetLineColor(kRed); > > gr1->Fit("pol1"); > TF1 *fline2=gr1->GetFunction("pol1"); > if(Constrain)fline2->SetParameter(0,0); > par[0] = fline2->GetParameter(0); > par[1] = fline2->GetParameter(1); > cout << par[0] << " " << par[1] << endl; > fline2->SetLineColor(kBlue); > > /********************************************************************/ > > -------------------------------------------------------------------------------- > Name: Eliveonly_ecal.gif > Eliveonly_ecal.gif Type: GIF Image (IMAGE/gif) > Encoding: BASE64
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