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## Re: [Help-gsl] Re: question about dirichlet lnpdf function (potential bu

**From**: |
Brian Gough |

**Subject**: |
Re: [Help-gsl] Re: question about dirichlet lnpdf function (potential bug) |

**Date**: |
Thu, 16 Jul 2009 20:45:20 +0100 |

**User-agent**: |
Wanderlust/2.14.0 (Africa) Emacs/22.2 Mule/5.0 (SAKAKI) |

At Mon, 13 Jul 2009 11:23:32 -0500,
Rodney Sparapani wrote:
>* [6] gsl_sf_lngamma_e(x = ???, result = ???) (optimized), at *
>* 0xfee1d178 (line ~1138) in "gamma.c"*
>* [7] gsl_sf_lngamma(x = ???) (optimized), at 0xfee1fdf4 (line ~1654) *
>* in "gamma.c"*
>* [8] gsl_ran_dirichlet_lnpdf(K = ???, alpha = ???, theta = ???) *
>* (optimized), at 0xfed9573b (line ~155) in "dirichlet.c"*
>* [9] gsl_ran_dirichlet_pdf(K = ???, alpha = ???, theta = ???) *
>* (optimized), at 0xfed954dc (line ~133) in "dirichlet.c"*
>* [10] main(), line 8 in "dirichlet.c"*
>* *
>* It looks like we have log-gamma-function(0) which is 0. However,*
>* it is throwing an error. Should it not just return 0?*
You're right that the GSL function signals an error which is unwanted
here. lngamma(0) is infinity and gsl_sf_lngamma gives an overflow
error, but since the infinity is in the denominator of the final
result there is no need for the error.
--
Brian Gough
(GSL Maintainer)
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