Problem getting the Sumw2 on ratio from normalized plots

Alkass · July 17, 2013, 6:42pm

Hi

I am trying to get the ratio of two normalized plots

       pad1->cd();
        pad1->SetLogy();

        Full->Scale(1/Full->Integral());
        Fast->Scale(1/Fast->Integral());
        
        Full->SetLineColor(kRed);
        Fast->SetLineColor(kBlue);
        Full->SetTitle("Comparison");
        Full->Draw();
        Fast->Draw("same");     
///////now the ratio plot

         pad2->cd();
               
        ///this is for the ratio 
        TH1F *ratio = (TH1F*)Full->Clone();
        ratio->Sumw2();
        ratio->Divide(Fast);
        ratio->GetYaxis()->SetNdivisions(5);
        ratio->Draw("pE");

my problem is that I get large error bars on the ratio plot (this does not happen if I dont normalize the plots) - Looks like that I am doing something wrong with the Sumw2, but cannot find what…

thanks