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MathGroup Archive 2005

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Re: Combinations

  • To: mathgroup at smc.vnet.net
  • Subject: [mg61716] Re: [mg61677] Combinations
  • From: Sseziwa Mukasa <mukasa at jeol.com>
  • Date: Thu, 27 Oct 2005 05:01:43 -0400 (EDT)
  • References: <200510260501.BAA18717@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

On Oct 26, 2005, at 1:01 AM, xxxxyz at abv.bg wrote:

> Hi,
>
> Is there any way to generate combinations per turn in a cycle? I mean
> first generate one combination, do something, generate next, do the
> same thing ...
>
> Thanks.

The combinations are called KSubsets in Mathematica, the  
Combinatorica package contains the necessary routines.  The first  
KSubset in lexicographic order is simply Range[k], you can use  
NextKSubset to see the others for example:

<<DiscreteMath`Combinatorica`
Block[{subset = Range[3]},Prepend[Table[subset = NextKSubset[Range 
[5], subset], {4}], Range[3]]]

will return the first 5 subsets of length 3 of {1,2,3,4,5} in  
lexicographic order.  There are functions to get the KSubsets in  
other orders in Combinatorica, I suggest you read the Help Browser  
information or read "Computational Discrete Mathematics:  
Combinatorics and Graph Theory with Mathematica" by Steven Skiena and  
Sriram Pemmaraju for more information on the package.

Regards,

Ssezi



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