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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 4:31 PM
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On Mar 28, 4:06 am, gsgs <> 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).

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