Re: definition of binomial error in histogram division?

From: Lorenzo Moneta <Lorenzo.Moneta_at_cern.ch>
Date: Wed, 18 Jul 2007 17:43:25 +0200


Hi Gero,
  for the factor c1 and c2 see

  https://savannah.cern.ch/bugs/?20722

Cheers

  Lorenzo
On Jul 4, 2007, at 7:52 AM, Gero Flucke wrote:

> On Tue, 3 Jul 2007, Rene Brun wrote:
>
>> Please read comments in the doc of TH1::Divide at
>> http://root.cern.ch/root/htmldoc/src/TH1.cxx.html#hh46dE
>>
>> When using the pro release 5.16 the error in bin1 is null.
>
> Hi Rene,
> while this makes sense (and simplifies the code) I wonder whether
> it was
> really intended to ignore the factors c1 and c2 in case of dividing
> histograms with binomial errors, which 'slipped in' now (not being
> mentioned in the commit log of TH1.cxx rev. 1.347!). I think that
> factors
> should be treated as if all histogram entries would have been weighted
> with this factor. A useful error for dividing weighted histograms with
> binomial errors has been introduced by Lorenzo in rev. 1.303.
>
> I did not check whether the old code after 1.303 and before 1.347
> treated
> the factors c1/2 correctly as weights, though.
>
> Cheers
>
> Gero
>
>>> Hi,
>>>
>>> In ROOT 5, the binomial error I expect to get with the "B" option in
>>> histogram
>>> division isn't the "standard" binomial error.
>>> What is its precise definition? If it's a bug it should be fixed,
>>> if it's not, the documentation should be updated.
>>>
>>> I attach an example where I expect to see an error of 0, but
>>> it's 0.0496 instead.
>>>
>>> Regards,
>>> Suyong
>>>
>>> --------------------------------------------------------------------
>>> ----
>>>
>>> {
>>> TH1F *h1 = new TH1F("h1", "Demonimator", 1, 0.0, 1.0);
>>> TH1F *h2 = new TH1F("h2", "Numerator", 1, 0.0, 1.0);
>>>
>>> h1->Sumw2();
>>> h2->Sumw2();
>>>
>>> h1->Fill(0.5,10.0);
>>> h2->Fill(0.5,10.0);
>>>
>>> h1->Divide(h1, h2, 1.0, 1.0, "B");
>>> }
>
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Received on Wed Jul 18 2007 - 17:44:24 CEST

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