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MathGroup Archive 1997

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Re: Help ! complex permutations

  • To: mathgroup at smc.vnet.net
  • Subject: [mg7054] Re: [mg6965] Help ! complex permutations
  • From: Robert Pratt <rpratt at math.unc.edu>
  • Date: Sat, 3 May 1997 22:04:46 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

I believe the command to use in Mma 2.2.2 was Strings, which now appears to 
have been relegated to the Combinatorica standard package in Mma 3.0.

Needs["DiscreteMath`Combinatorica`"]

?Strings
"Strings[l, n] constructs all possible strings of length n from the 
elements of list l."

Strings[{a,b},2]
{{a,a},{a,b},{b,a},{b,b}}

Strings[{a,b},3]
{{a,a,a},{a,a,b},{a,b,a},{a,b,b},{b,a,a},{b,a,b},{b,b,a},{b,b,b}}

Rob Pratt
Department of Mathematics
The University of North Carolina at Chapel Hill
CB# 3250, 331 Phillips Hall
Chapel Hill, NC  27599-3250

rpratt at math.unc.edu

http://www.math.unc.edu/Grads/rpratt/

On Wed, 30 Apr 1997, 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?
> 
> Can anyone point me in the right direction? A reference, clue or even
> an algorithm would be very welcome ;)
> 
> TIA
> 
> Robert_p
> 
> 
> 


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