Extra parameter for DirichletDistribution
- To: mathgroup at smc.vnet.net
- Subject: [mg121912] Extra parameter for DirichletDistribution
- From: Todd <johnson.todd.r at gmail.com>
- Date: Thu, 6 Oct 2011 04:24:18 -0400 (EDT)
- Delivered-to: l-mathgroup@mail-archive0.wolfram.com
Can anyone tell me why DirichletDistribution in Mathematica 8 requires
k+1 parameters for a k-dimensional distribution and why the extra
parameter cannot be 0, which would give results similar to other
software packages that require only k parameters. The function of the
extra parameter is clear from the mean of the 2D distribution given in
the help file:
Namely, the mean of DirichletDistribution[a1, a2, a3] is {a1/
(a1+a2+a3), {a2/(a1+a2+a3)}.
In this case, setting a3 to 0 would give me the desired result, but
the function requires a3 to be positive.
I noticed that a definition of DirichletDistribution from an older
Wolfram tutorial required only k parameters for a k-dimensional
distribution.
Todd