Re: permutations
- To: mathgroup at smc.vnet.net
- Subject: [mg62421] Re: permutations
- From: "Scout" <Scout at nodomain.com>
- Date: Thu, 24 Nov 2005 06:33:20 -0500 (EST)
- References: <dm1jov$n4c$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
"Francisco Gutierrez" <fgutiers2002 at yahoo.com>
> 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
>
>
>
Hi Francisco,
have you already tried to use the NextPermutation[] function?
Let's say
l={x1,x2,x3,x4,x5,x6,x7,x8,x9,x10,x11,x12}
NextPermutations[ l ] gives
{x1,x2,x3,x4,x5,x6,x7,x8,x9,x10,x12,x11}
that differ from the previous list in only one change.
So, applying repeatedly NextPermutation[] you can cover
all the Length[l]! permutations.
I hope this help you,
~Scout~