OK, that makes sense. Thanks!
Personally, however, I do not see a reason why the first argument must
be unsigned int, as opposed to int. The reason why I say that is that
the Poisson distribution is a distribution that gives positive
probability to non negative integers and zero to the negative ones. So
for negative int the 2 functions should return zero. That is just my
opinion though.
Thanks again!
On 18/10/12 14:31, Rhys Ulerich wrote:
Hi Georgios,
Just to clarify: the function I am talking about is gsl_cdf_poisson_P, Not
gsl_ran_poisson_pdf that I mistakenly mentioned below. The function
gsl_ran_poisson_pdf (unsigned int k, double mu) is fine, and
gsl_ran_poisson_pdf(-1,5) returns the expected zero.
According to
http://www.gnu.org/software/gsl/manual/html_node/The-Poisson-Distribution.html
gsl_cdf_poisson_P also takes an unsigned int as the first argument.
Passing negative values to the function is impossible because the
first argument is unsigned.
That "gsl_ran_poisson_pdf(-1,5) returns the expected zero" is mere
happenstance. Somehow feeding the function "(unsigned) -1" ==
4294967295 (according to my current system) is producing the zero.
- Rhys
