Re: Help ! complex permutations
- To: mathgroup at smc.vnet.net
- Subject: [mg7023] Re: [mg6965] Help ! complex permutations
- From: Lou Talman <me at talmanl.mscd.edu>
- Date: Fri, 2 May 1997 21:30:49 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
Robert Perkins wrote:
> I need to derive an algorithm, formula, which gives all the
> possiblities, combinations, for any 'n' out of 'm' with the proviso
> that any member of 'm' can be used multiple times and the selection
> sequence is significant.
>
> Taking a trivial example if the input list 'm' is
>
> {a,b}
>
> the output list 'n' for any 2 gives
>
> {a,a},{a,b},{b,a},{b,b}
>
> For an output sequence of 3 from the same input list would give
>
> {a,a,a},{a,a,b},{a,b,b},{b,a,b},{b,b,a},{b,b,b}
>
> Life gets interesting for larger input sequences and ever larger
> output selections. How about the input list containing 10 members and
> the output list containing 20 members with the above rules applying?
I guess I don't understand the problem. Why aren't {a, b, a} and {b, a, a}
amongst the entries in that last list?
--Lou Talman