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

From: Corey Reed <cjreed_at_nikhef.nl>
Date: Wed, 28 Jul 2010 13:55:25 +0200


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.

Received on Wed Jul 28 2010 - 13:55:29 CEST

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