the function
Double_t TMath::Poisson(Double_t x, Double_t par)
{
// compute the Poisson distribution function for (x,par)
if (x<0) return 0;
if (x==0) return TMath::Exp(-par);
return TMath::Power(par,x)/TMath::Gamma(x+1)/TMath::Exp(par);
}
dosn't appear to work for x=0.... cannot imagine what the problem is!
root [28] TMath::Poisson(0.,2.)
(Double_t)0.00000000000000000e+00
root [29] TMath::Poisson(1.,2.)
(Double_t)2.70670566473225516e-01
root [30] TMath::Poisson(2.,2.)
(Double_t)2.70670566473225516e-01
root [31]
root [31]
root [31] TMath::Power(2,0)/TMath::Gamma(0+1)/TMath::Exp(2)
(double)1.35335283236612702e-01
root [32] TMath::Power(2,1)/TMath::Gamma(1+1)/TMath::Exp(2)
(double)2.70670566473225516e-01
root [33] TMath::Power(2,2)/TMath::Gamma(2+1)/TMath::Exp(2)
(double)2.70670566473225516e-01
--
Michael Gold
Department of Physics and Astronomy
University of New Mexico
Albuquerque, NM 87131
cell : 505-238-6155
phone: 505-277-2086, 505-277-3604
fax: 505-277-1520
email: gold@phys.unm.edu
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