func PoissonPdf(k uint32, mu float64) float64 { return float64(C.gsl_ran_poisson_pdf(C.uint(k), C.double(mu))) }
func PoissonPdf(k int, lambda float64) float64 { if k < 0 { return 0 } return float64(C.gsl_ran_poisson_pdf(C.uint(k), C.double(lambda))) }