Re: histogram subtraction and mean

No, I must disagree with you. ROOT computes the best possible value if the necessary information is available.
I am sure that we will get zillions of complaints if we were following your suggestion ::)

Rene

On 01/03/2011 15:59, Stefan Piperov wrote:
>
> I understand that mechanism, and the fact that computing moments from
> un-binned data is more precise, but it's also misleading. If I'm
> filling a histogram, then I want to know the charachteristics (e.g.
> moments) of the binned data, not the originals. I can always calculate
> the moments of the unbinned data if I wished.
>
> To me, at least, the default should be moments to be calculated from
> binned data. The other behaviour should be optional.
> But that might be quite a change on ROOT...
>
> Stefan.
>
>
>
> On Tue, 1 Mar 2011, Rene Brun wrote:
>
>> When you use TH1::Fill, ROOT can compute the moments precisely
>> because it has the original input values.
>> As soon as you make an operation (add, ssubtract, zoom, etc), the
>> only thing that we can do is to start from
>> the bin contents only with the approximation that all values in the
>> bin are at the center of the bin.
>>
>> Rene
>>
>>
>> On 01/03/2011 15:50, Stefan Piperov wrote:
>>>
>>> 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
>>> > >
>>> -------------------------------------------------------------------------
>>> > > >
>>> *---------------------------------------------------------------------*
>>>
>>> Stefan Piperov Mail: FNAL P.O.Box 500, MS 205, Batavia, IL-60510
>>> Phone: (630) 840-5176 E-Mail: piperov_at_fnal.gov
>>> *---------------------------------------------------------------------*
>>>
>>> "Give a skeptic an inch... and he'll measure it."
>>>
>>
>>
>
> *---------------------------------------------------------------------*
> Stefan Piperov Mail: FNAL P.O.Box 500, MS 205, Batavia, IL-60510
> Phone: (630) 840-5176 E-Mail: piperov_at_fnal.gov
> *---------------------------------------------------------------------*
> "Give a skeptic an inch... and he'll measure it."
>
Received on Tue Mar 01 2011 - 16:07:55 CET