From maechler at stat.math.ethz.ch  Wed Mar 26 11:02:37 2008
From: maechler at stat.math.ethz.ch (maechler at stat.math.ethz.ch)
Date: Wed, 26 Mar 2008 11:02:37 +0100 (CET)
Subject: [Rd] choose fails a fundamental property of binomial
	coefficients (PR#11035)
Message-ID: <20080326100237.8B9F42834619@mail.pubhealth.ku.dk>

>>>>> "JL" == Jerry Lewis <Jerry.Lewis at biogenidec.com>
>>>>>     on Wed, 26 Mar 2008 05:10:04 +0100 (CET) writes:

    JL> Full_Name: Jerry W. Lewis Version: 2.7.0 (2008-03-23
    JL> r44847) OS: Windows XP Professional Submission from:
    JL> (NULL) (71.184.230.48)


    JL> choose(n,k) = choose(n,n-k) is not satisfied if either

    JL> 1. n is a negative integer with k a positive integer
    JL> (due to automatically returning 0 for n-k<0)


    JL> 2. n is not an integer with k a positive integer (due to
    JL> rounding n-k to an integer, compounded by automatically
    JL> returning 0 if n<0 which implies n-k<0)


I think you have not really understood from help(choose)
that we have

     choose(n,k) :=  n(n-1)...(n-k+1) / k!

defined for non-negative integer k and arbitrary real n

This definition has the very important property that it is used
in the 'binomial theorem' and everything depending on that
theorem,

   (1 + x) ^ \alpha =  \sum_{k=0}^\infty  choose(x,k) x^k

which holds   for all |x| < 1   for all \alpha \in \R

-------

Your "fundamental" property does only hold when  n is
non-negative integer.

Definitely no bug in R here!

Martin Maechler, ETH Zurich



[Rd] choose fails a fundamental property of binomial coefficients (PR#11035)
maechler at stat.math.ethz.ch