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Re: Combinatorics question

• To: mathgroup at smc.vnet.net
• Subject: [mg3318] Re: Combinatorics question
• From: "Don J. Orser" <djorser at intrepid.net>
• Date: Mon, 26 Feb 1996 02:55:37 -0500
• Organization: BRM INC.
• Sender: owner-wri-mathgroup at wolfram.com

<PESCC at CUNYVM.CUNY.EDU> wrote:
>Can somenone help me find the following:
> 
>I have a list of 20 numbers, and I would like to list all the
>combinations of these numbers taken 6 at a time.  The Binomial
>function tells me there are 38760, but I would like to actually
>see all of them.
>Thanks in advance for your help.
>
I have encountered the need to do this type of thing in combinatorial 
geometry, where much larger numbers are in involved.  There are a number 
of algorithms available and which one you choose will in part depend on 
the order you wish them to appear.  However, unless you are going to 
actually eyeball everyone,  you need to perform whatever test/computation 
etc., you plan on doing to each one on the fly.  There is a standard 
recursive algorithm for doing this which is nice to use if the function 
is of all lower order combinations, e. g., intersections of elements of 
the power set.

If it makes sense, tell us more about what you want to do with these 
combinations.

Hope this helps.

Don J. Orser
djorser at intrepid.net


>




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