Re: Re: Computing nCr how?
- To: mathgroup at smc.vnet.net
- Subject: [mg94942] Re: [mg94918] Re: Computing nCr how?
- From: Murray Eisenberg <murray at math.umass.edu>
- Date: Wed, 31 Dec 2008 06:08:50 -0500 (EST)
- Organization: Mathematics & Statistics, Univ. of Mass./Amherst
- References: <200812301055.FAA13167@smc.vnet.net>
- Reply-to: murray at math.umass.edu
Why the obscure abbreviations "Combin" and "Permut". Why not at least "Combine" and "Permute", or even the more readable "Combinations" and "Permutations"? Dana DeLouis wrote: >> ... I cant find the function ...to compute nCr > > I remember my very first question with Mathematica was "Where is Permut nPr ?" > I was a little dismayed (and still am a little) that the program didn't have > the same function as found in Spreadsheets. I remember thinking that this > program must not have very many functions. (till I bought the book!) :>) > > Switching from a Spreadsheet to Mathematica, my very first two programs were: > > Combin[n_, k_] := Binomial[n, k] > Permut[n_, k_] := n!/(n - k)! > > However, for speed, I now use this: > Permut[a_, b_] := Pochhammer[1 + a - b, b] > > The second version is faster, but the first version will reduce here... > Permut[a, b]/a! > 1/(a - b)! > > Dana > > Affan wrote: >> Hi, >> I know this sounds simple but I cant find the function in mathematica >> to compute nCr (i.e. number of combination for n obj chosen in groups >> of r). Can anyone help? >> >> Thanks > -- Murray Eisenberg murray at math.umass.edu Mathematics & Statistics Dept. Lederle Graduate Research Tower phone 413 549-1020 (H) University of Massachusetts 413 545-2859 (W) 710 North Pleasant Street fax 413 545-1801 Amherst, MA 01003-9305