Hi Dan,
both values for the integrals are accurate.
The integral of the Poisson function should not be
1 always. It is 1 (approximately) for x0 >> 1, but
goes to 0 when x0 --> 0.
Smbat
> Hi,
>
> i kind of asked this question a week and a half ago but i got no responce
> so i will try again..
>
> root vers: 3.05/07
>
> To what accuracy can i use the poisson function?
>
> I do:
> poiss1=new TF1("poiss1","TMath::Poisson(x,[1])",0,99);
>
> float x0=3;
> poiss1->SetParameter(1,x0);
> poiss1.Integral(0,99)
>
> >>9.82143583403792597e-01
>
> float x0=0.3;
> poiss1->SetParameter(1,x0);
> poiss1.Integral(0,99)
>
> >>5.85493726744197751e-01
>
> ..i guess the first case is accurate to at least a few percent? ..how
> about the second case? ..what is the lower limit to which i can set x0 and
> still get a reasonable answer?
>
> cheers,
>
> Dan.
>
>
>
>
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