Poisson errors in histograms, EBinErrorOpt

Hi all,

The error, as computed for TH1 histograms, when one uses the Sumw2() function as well is the “the error per bin is computed as the sqrt(sum of squares of weights)”.

I have background histograms with very few counts. I want to change it to Poisson errors per bin. I have seen a Public Types EBinErrorOpt{…} and a function called SetBinErrorOption(EBinErrorOpt type). However, whatever input I put into SetBinErrorOption doesn’t produce the correct results.

How do I implement this change?


If the histogram is weighted, the error is not anymore Poisson and it is computed always as sqrt(sum of squares of weights)


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