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Re: rules on vector sequence
*To*: mathgroup at smc.vnet.net
*Subject*: [mg98065] Re: rules on vector sequence
*From*: Francesco <b.gatessucks at gmail.com>
*Date*: Sun, 29 Mar 2009 02:45:33 -0500 (EST)
*References*: <gqkurj$47q$1@smc.vnet.net>
Not practical for n>~6 :
n = 4;
elements = {-2, -1, 0, 1, 2};
rules[entry_] :=
Total[entry] ==
0 && (Count[entry, 0] == (n - 2) || Count[entry, 0] == (n - 4) )
Select[Tuples[elements, n], rules[#] &]
-Francesco
Filippo Miatto wrote:
> Dear all,
> I need to generate all the vectors, of a given length N, that have
> these three properties:
>
> 1- the entries have to be among -2,-1,0,1,2
> 2- the sum of all the entries has to be 0
> 3- only two or four of the entries can be different from 0
>
> do you have any suggestions on how i can do that? i tried something
> but without success.. expecially i don't know how to implement the
> third rule..
> thank you in advance!
> Filippo
>
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