[ROOT] Add or Substract histogram problem.

From: Kai Yi (yik@fnal.gov)
Date: Wed Jan 16 2002 - 02:48:23 MET 

Hi, All experts,
    I used yhe follwoing code to subtract 2 histograms (a sideband
subtraction):

    TH1F *htemp = (TH1F*)z0hist->Clone();
    htemp->Add((TH1 *)z0histsideband,-1/2.4);

    I think I got the right result except that Nent was reported to be the
sum not the difference of the 2 histograms. The integral from

htemp->Integral(0,htemp->GetNbinsX()+1

was the right number of entries I expected. Why is Nent incorrect?

Thanks,

Kai Yi

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