[R] Function to compute the multinomial beta function?

[Robin Hankin]

It's usually better to build vectorization in to functions:

 > beta3<- function (n1, n2, n3) 
exp(lgamma(n1)+lgamma(n2)+lgamma(n3)-lgamma(n1+n2+n3))
 > f <- function(x){exp(sum(lgamma(x))-lgamma(sum(x)))}
 > beta3(5,3,8)
[1] 1.850002e-07
 > f(c(5,3,8))
[1] 1.850002e-07
 >

rksh


On 07/06/2010 01:54 AM, Robert A LaBudde wrote:
> 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
>


-- 
Robin K. S. Hankin
Uncertainty Analyst
University of Cambridge
19 Silver Street
Cambridge CB3 9EP
01223-764877