[Jprogramming] permutation list

[Tirrell, Jordan (Consultant)]

I don't think you'd ever want to use perm dyadically.

perm=. ! A.&i. ]

perm y gives all !y permutaions of y objects.
x perm y gives the first x!y permutations of y objects.

So dyadic perm is defined as the first x!y (or # x comb y) items of monadic perm. I think this is simply a consequence of the intended monadic definition.


-----Original Message-----
From: programming-bounces at jsoftware.com [mailto:programming-bounces at jsoftware.com] On Behalf Of Raul Miller
Sent: Tuesday, June 26, 2012 2:14 PM
To: Programming forum
Subject: Re: [Jprogramming] permutation list

They are certainly different.

   2 comb 3
0 1
0 2
1 2
   2 perm 3
0 1 2
0 2 1
1 0 2


In general, for n of m permutations and n of m combinations, the permutations are going to be longer (length m instead of length n).
But the number of distinct items will be the same.

--
Raul

On Tue, Jun 26, 2012 at 2:09 PM, Devon McCormick <devonmcc at gmail.com> wrote:
> I thought that in the usual mathematical definition, combinations and 
> permutations differ: for permutations, order matters; for 
> combinations, it does not.  Under this definition, the combinations of
> 3 things is just " i. 3 " - assuming we don't allow replacement?  If 
> we do allow replacement, the permutations of 3 things are given by "
> {3$<i.3 " and the combinations by something like " ~./:~&.>,{3$<i.3 ".
>
> Does this seem right?
>
> On Tue, Jun 26, 2012 at 12:51 PM, Raul Miller <rauldmiller at gmail.com> wrote:
>> Note that the number of combinations and the number of permutions are the same.
>>
>> And, perm is just: ! A.&i. ]
>>
>> It seems like there ought to be a way of putting the permutations in 
>> 1 to 1 correspondence with the combinations (to give us a concise 
>> expression for combinations).
>>
>> --
>> Raul
>>
>> On Tue, Jun 26, 2012 at 12:41 PM, ed bierly <ebierly at gmail.com> wrote:
>>> yes combinations not permutations
>>> thought there might be a way that didn't loop thank you for the 
>>> references
>>>
>>> On Tue, Jun 26, 2012 at 12:30 PM, R.E. Boss <r.e.boss at planet.nl> wrote:
>>>
>>>> 4 comb 10
>>>>
>>>>
>>>> R.E. Boss
>>>>
>>>>
>>>> > -----Oorspronkelijk bericht-----
>>>> > Van: programming-bounces at jsoftware.com [mailto:
>>>> programming-bounces at jsoftware.com] Namens ed bierly
>>>> > Verzonden: dinsdag 26 juni 2012 18:15
>>>> > Aan: programming at jsoftware.com
>>>> > Onderwerp: [Jprogramming] permutation list
>>>> >
>>>> > what is the best way to get this list of 210 vectors?
>>>> >
>>>> > 4!10
>>>> > -----------------------------------------------------------------
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>
>
>
> --
> Devon McCormick, CFA
> ^me^ at acm.
> org is my
> preferred e-mail
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