Re: histogram subtraction and mean

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
> -------------------------------------------------------------------------
Received on Tue Mar 01 2011 - 12:57:25 CET