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Topic: hypogeometric sum
Replies: 11   Last Post: Mar 31, 2008 3:25 PM

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Dann Corbit

Posts: 1,424
Registered: 12/8/04
Re: hypogeometric sum
Posted: Mar 28, 2008 4:38 PM
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On Mar 28, 1:31 pm, user923005 <dcor...@connx.com> wrote:
> On Mar 28, 4:06 am, gsgs <ster...@aol.com> wrote:
>

> > how do I efficiently calculate or approximate
>
> > SUM [i=0..k] hypergeometrical(i;r,n,w)
>
> > ?
>
> > hypergeometrical(i;r,n,w)=binomia(w,i)*binomial(n-w,r-i)/binomial(n,r)
>
> > this is for testing large gene-databases for recombinations
>
> I am assuming that all values are integral and that you have a
> mathematics system that can compute the answers without overflow (not
> always an easy task if the inputs are large).
>
> Precompute the binomail coefficients and store them in a table.
> Then you will have this:
> binomial[w][i] * binomial[n-w][r-i]/binomial[n][r]
> which is O(1).


I have a very large Pascal's triangle precomputed, if you would like a
copy.
I can also generate one for whatever size you need (I have a program
that generates the programs).



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