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MathGroup Archive 1997

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Re: Help ! complex permutations

  • To: mathgroup at smc.vnet.net
  • Subject: [mg7023] Re: [mg6965] Help ! complex permutations
  • From: Lou Talman <me at talmanl.mscd.edu>
  • Date: Fri, 2 May 1997 21:30:49 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

Robert Perkins wrote:

> I need to derive an algorithm, formula, which gives all the
> possiblities, combinations, for any 'n' out of 'm' with the proviso
> that any member of 'm' can be used multiple times and the selection
> sequence is significant. 

> 

> Taking a trivial example if the input list 'm' is
> 

> 	{a,b} 

> 

> the output list 'n' for any 2 gives
> 

> 	{a,a},{a,b},{b,a},{b,b}
> 

> For an output sequence of 3 from the same input list would give
> 

> 	{a,a,a},{a,a,b},{a,b,b},{b,a,b},{b,b,a},{b,b,b}
> 

> Life gets interesting for larger input sequences and ever larger
> output selections. How about the input list containing 10 members and
> the output list containing 20 members with the above rules applying?

I guess I don't understand the problem.  Why aren't {a, b, a} and {b, a, a}  
amongst the entries in that last list?

--Lou Talman


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