[Rivet] rivet: normalizing histograms to variable bin width

[Oldrich Kepka]

Hi Andy,


On 17 March 2014 13:20, Andy Buckley <andy.buckley at cern.ch> wrote:
> Hi Oldrich (and CC'ing the Rivet list -- please send to that rather than
> me directly!),
>
> In the API of YODA the bin width is taken into account when calling the
> HistoBin::height() method:
>
> https://yoda.hepforge.org/trac/browser/include/YODA/HistoBin1D.h#L97
>
> (and a corresponding divide by x-y bin area in HistoBin2D)
>
> By "normalize to bin width", I'm guessing that you mean "divide by
> integral = sum of bin & overflows weight sums". For bins, the sum of
> weights is the area rather than the height. Is that what you had in
> mind? If so (and I'm sure this is the physically correct approach) then
> this is already what YODA does:
>
> Histo1D::normalize:
>   https://yoda.hepforge.org/trac/browser/include/YODA/Histo1D.h#L146
> calls Histo1D::integral:
>   https://yoda.hepforge.org/trac/browser/include/YODA/Histo1D.h#L298
> calls Histo1D::sumW:
>   https://yoda.hepforge.org/trac/browser/src/Histo1D.cc#L43
>
> Does that answer your question?


In the mkScatter function that converts Histo1D etc. to
TGraphAsymmErrs-like Scatter2Ds.

This answers my question. I knew I must have been missing something
fundamental. Histograms are converted to scatter, where the height()
comes into play, so that the plotted result is a differential cross
section.

Thanks,
Oldrich



we use the
> Bin::height() function so that the plotting will look correct, but
> internally the area() == sumW() are much more important.
>
> Andy
>
>
> On 17/03/14 12:38, Oldrich Kepka wrote:
>> Hi Andy,
>>
>> sorry for this basic question. Is there already an implementation of a
>> method normalizing histograms to produce differential cross section,
>> i.e. normalizing to bin width.
>>
>> Presumably, there must be, because there are several differential
>> cross sections implemented. I am probably missing something, but I
>> cannot find the place where the bin widtf is taken into account
>> (looking through Histo1D, Bin1D, Dpn1D ... ). The usual Analysis
>> scale/normalize methods boil down to scaleW of Dbn1D; scaling
>> according to global desired factor.
>>
>> Otherwise, I would go for something like this.
>>
>>      _h_ZZ_ZpT.scale( norm);
>>       for(size_t i = 0; i< _h_ZZ_ZpT-> numBins(); i++) {
>>                 _h_ZZ_ZpT->bin(i). scaleW( 1/_h_ZZ_ZpT->bin(i). width() );
>>          }
>>        normalize(_h_ZZ_ZpT    , 1);
>>
>> http://hepdata.cedar.ac.uk/view/ins1203852
>>
>>
>> Thanks,
>> Oldrich
>>
>
>
> --
> Dr Andy Buckley, Royal Society University Research Fellow
> Particle Physics Expt Group, University of Glasgow / PH Dept, CERN