Re: ROOT::Math::poisson_pdf(0,0)=NaN while TMath::PoissonI(0,0)=1

From: Axel Naumann <Axel.Naumann_at_cern.ch>
Date: Wed, 28 Jul 2010 18:09:33 +0200


Hi Corey,

thanks for your report! Lorenzo will reply to you when he is back from vacation.

Cheers, Axel.

Corey Reed wrote on 07/28/2010 01:55 PM:
> Hi,
>
> Just in case anyone (else) encounters this, I thought I would post it to
> this list.
>
> In Root 5.26.00/b,
>
> root [9] ROOT::Math::poisson_pdf(0,0)
> (double)nan
>
> root [11] TMath::PoissonI(0,0)
> (Double_t)1.00000000000000000e+00
>
> I personally would have expected the poisson_pdf to give 1 (the chance
> to get 0 events in the limit that the mean goes to 0).
>
> I don't know if this behavior is intended or not.
>
> - Corey
>
>
Received on Wed Jul 28 2010 - 18:09:45 CEST

This archive was generated by hypermail 2.2.0 : Wed Jul 28 2010 - 23:50:02 CEST