Excellent. a[i,j] = v[r+1] was essentially the mapping I had in mind. 
Thanks for sharing the code!

On Friday, July 31, 2015 at 7:15:30 AM UTC-4, Tamas Papp wrote:
>
> On Fri, Jul 31 2015, Christopher Fisher <[email protected] <javascript:>> 
>
> wrote: 
>
> > Thank you Tamas. I added return a and restructured the code (I 
> > think some  formatting was lost when pasting). Based on the 
> > examples I tested, it  appears to work. Can you recommend an 
> > efficient method of inputing an array  of numbers. For example: 
> > 
> > a = [10,12] 
> > 
> > p = perm_matrix(a,2) 
> > 
> > p = [10 10; 10 12; 12 10; 12 12] 
> > 
> > I could probably hack something together that maps elements of a 
> > to the  elements of p (0 through n-1), but you might have a more 
> > efficient and  elegant solution. 
>
> A trivial modification takes care of that, see 
> https://gist.github.com/tpapp/43131b48f1afd97f1018 
>
> > Regarding the second question, the combinations function (I 
> > believe this is  what you were referring to) would treat (1,2) 
> > and (2,1) as  indistinguishable. For example, the code below 
> > yields only three unordered  pairs rather than six ordered pairs 
>
> Just use permutations --- see example in the gist above. 
>
> Best, 
>
> Tamas 
>

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