R help - Jul 2010 - Function to compute the multinomial beta function?

Dear R-users,

Is there an R function to compute the multinomial beta function? That is, the
normalizing constant that arises in a Dirichlet distribution. For example, with
three parameters the beta function is Beta(n1,n2,n2) =
Gamma(n1)*Gamma(n2)*Gamma(n3)/Gamma(n1+n2+n3)

Thanks in advance for any assisstance.

Regards,
Greg



	[[alternative HTML version deleted]]

How about this?

mbeta <- function(...) { 
    exp(sum(lgamma(c(...)))-lgamma(sum(c(...))))
}
 
> gamma(5)*gamma(6)*gamma(7)/gamma(18)
[1] 5.829838e-09
> mbeta(5,6,7)
[1] 5.829838e-09



On Mon, 2010-07-05 at 17:10 -0400, Gregory Gentlemen
wrote:
> Dear R-users,
> 
> Is there an R function to compute the multinomial beta function? That is,
the normalizing constant that arises in a Dirichlet distribution. For example,
with three parameters the beta function is Beta(n1,n2,n2) =
Gamma(n1)*Gamma(n2)*Gamma(n3)/Gamma(n1+n2+n3)
> 
> Thanks in advance for any assisstance.
> 
> Regards,
> Greg
> 
> 
> 
> 	[[alternative HTML version deleted]]
> 
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-- 
Matthew S. Shotwell
Graduate Student
Division of Biostatistics and Epidemiology
Medical University of South Carolina
http://biostatmatt.com

At 05:10 PM 7/5/2010, Gregory Gentlemen wrote:
>Dear R-users,
>
>Is there an R function to compute the multinomial beta function? 
>That is, the normalizing constant that arises in a Dirichlet 
>distribution. For example, with three parameters the beta function 
>is Beta(n1,n2,n2) = Gamma(n1)*Gamma(n2)*Gamma(n3)/Gamma(n1+n2+n3)
 > beta3<- function (n1, n2, n3) 
exp(lgamma(n1)+lgamma(n2)+lgamma(n3)-lgamma(n1+n2+n3))
 > beta3(5,3,8)
[1] 1.850002e-07

===============================================================Robert A.
LaBudde, PhD, PAS, Dpl. ACAFS  e-mail: ral at lcfltd.com
Least Cost Formulations, Ltd.            URL: http://lcfltd.com/
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