Re: histogram subtraction and mean

From: Stefan Piperov <piperov_at_fnal.gov>
Date: Tue, 1 Mar 2011 16:50:34 +0200

Well, probably the more interesting question is why before operations the moments are not calculated using the bin contents? That's a default which has always puzlled me. Stefan.

On Tue, 1 Mar 2011, Rene Brun wrote:

> What you get is perfectly normal.
> Following an operation on your histogram (Add, Substract, Rebin, etc) the
> statitics for moments (mean, sigma, etc)
> are recomputed from the bin contents, assuming the center of the bin.
>
> Rene Brun
>
>
> On 01/03/2011 12:37, Margar Simonyan wrote:
>> Hello ROOTTalk
>>
>> I get strange results after histogram subtraction, the attached script
>> written in Python demonstrates the issue. My goal is to subtract
>> background from signal+background distribution and get meaningful
>> results for mean.
>> There are several unexpected (for me) results:
>> First, the mean changes after subtracting empty histogram, this is not
>> a big issue. Second, after subtracting background I don't get exactly
>> the signal value. Third, rebinning before subtracting changes the
>> results once more.
>> Can somebody explain this? I am using ROOT 5.26/00e complied on SLC5
>> with gcc43.
>>
>> Thanks,
>> Margar
>> -------------------------------------------------------------------------
>> Dr Margar Simonyan, post-doctoral researcher
>> Niels Bohr Institute, Copenhagen University
>> -------------------------------------------------------------------------
>
>
>

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  Stefan Piperov      Mail: FNAL P.O.Box 500, MS 205, Batavia, IL-60510
  Phone: (630) 840-5176                        E-Mail: piperov_at_fnal.gov
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"Give a skeptic an inch... and he'll measure it." Received on Tue Mar 01 2011 - 15:50:43 CET