Re: Permutations of a sequence - variation 2

*To*: mathgroup at smc.vnet.net*Subject*: [mg76261] Re: Permutations of a sequence - variation 2*From*: Bill Rowe <readnewsciv at sbcglobal.net>*Date*: Fri, 18 May 2007 06:26:59 -0400 (EDT)

On 5/17/07 at 6:01 AM, vs at it.uu.se (Virgil Stokes) wrote: >Suppose I have a sequence: >{1,2,3,4,5} >and I would like to generate all permutations of this sequence with >the constraint that the last element not be the same as the first. >Thus, >{2,5,3,1,4} >is acceptable; but, >{2,5,3,4,1} >is not. >Are there Mathematica commands that allow this to be done >efficiently for a sequence {1,2,...,n}? Note, the solution of this >problem can be used to solve the earlier problem that I posted on >sequence permutations. The brute force way of generating all possible permutations and deleting those you don't want is fairly easy to do, i.e., for n=3 In[5]:= DeleteCases[Permutations@Range[3], {__, 1}] Out[5]= {{1, 2, 3}, {1, 3, 2}, {2, 1, 3}, {3, 1, 2}} And if n isn't too large, I suspect this likely to be the quickest, most efficient way. -- To reply via email subtract one hundred and four