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MathGroup Archive 2005

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Re: permutations

  • To: mathgroup at smc.vnet.net
  • Subject: [mg62422] Re: [mg62418] permutations
  • From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
  • Date: Thu, 24 Nov 2005 06:33:21 -0500 (EST)
  • References: <200511231127.GAA23646@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

On 23 Nov 2005, at 20:27, Francisco Gutierrez wrote:

>
> Dear Group:
>   If I do for example:
>   Permutations[{x1,x2,x3,x4,x5,x6,x7,x8,x9,x10,x11,x12}],
>   my computer runs out of memory.
>   This is not such a poor computer.  Actually, I would need to do  
> permutations of lists of Length 20, perhaps 25.  I am aware these  
> calculations are big (Length[x]!), but I wonder if there is some  
> way around the problem. Compilating Permutations? But then how? Can  
> somebody help me?
>   Francisco Gutiérrez
>
> 		

I don't think that even a 64 bit Mathematica on a 64 bit computer  
with the maximum amount of Ram will help you here. Compiling  
certainly won't. However, I can't possibly see any reason why you  
would need to have such a list. Have you looked at the function  
NextPermutation and UnrankPermutation from the Combinatorica package?  
Most likely what you want to do can be done by making use of these  
functions without trying to construct impossibly large lists.

Andrzej Kozlowski


  • References:
    • permutations
      • From: Francisco Gutierrez <fgutiers2002@yahoo.com>
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