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 >