On 27 October 2011 14:18, <[email protected]> wrote:
> On Wed, Oct 26, 2011 at 10:50 PM, Alexandre Passos
> <[email protected]> wrote:
> > On Wed, Oct 26, 2011 at 22:48, Robert Layton <[email protected]>
> wrote:
> >> You have it correct. I haven't done this level of algebra for a while,
> so
> >> I'll need to work it out.
> >> If I have it correctly, I should be able to do:
> >> log(a!) + log(b!) + log((N-a)!) + log((N-b)!) - log(N!) - log(n!) -
> >> log((a-n)!) - log((b-n)!) - log((N-a-b+n)!),
> >> then apply Stirling and simplify?
> >
> > Exactly.
>
> gammaln works pretty well in scipy.stats.distributions. I would try
> that first, since it's easy, unless you expect only large numbers.
>
> Josef
>
> >
> > --
> > - Alexandre
> >
> >
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>From my initial workings, Stirling collapses quite well for this equation
and should be fairly good.
I'll try it in the next couple of days and see.
I had a way of doing it that would be really robust, but really slow. Expand
each of the factorials on the denominator and numerator separately and store
as separate lists. Then remove all terms common to both lists and multiply
the results. However, this heavily uses append and would be too slow for
large value of N.
Thanks!
- Robert
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