Re: permutations

*To*: mathgroup at smc.vnet.net*Subject*: [mg62450] Re: permutations*From*: dh <dh at metrohm.ch>*Date*: Thu, 24 Nov 2005 06:33:50 -0500 (EST)*References*: <dm1jov$n4c$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Hi Francisco, The number of permutations can easily be calcultaed by n!. For n=20 this gives a number of the order of 10^18. You will certainly not be able to store this in the near future. What can you do? Although I can not imagine what you want to do with so many permutations, you could still use: NextPermutation from the package: DiscreteMath`Combinatorica`. This will give you one permutation at a time. Of course, it will take some patience to go through all permutations! Daniel 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 > > >