MATLAB Central Newsreader - Permutations in matlab

Permutations in matlab

Midhun — Tue, 18 Aug 2009 05:53:02 -0400

Hello,
How can I do permutations in matlab ?

In Matalb , the command : ' combntns(set,subset)' returns a matrix whose rows are the various combinations that can be taken of the elements of the vector set of length subset.

How can I create a 'permutational' set instead of a 'combinatorial' set ?

Re: Permutations in matlab

Husam Aldahiyat — Tue, 18 Aug 2009 07:23:03 -0400

"Midhun " <midhunjoyp@gmail.com> wrote in message <h6dfju$juk$1@fred.mathworks.com>...
> Hello,
> How can I do permutations in matlab ?
>
> In Matalb , the command : ' combntns(set,subset)' returns a matrix whose rows are the various combinations that can be taken of the elements of the vector set of length subset.
>
> How can I create a 'permutational' set instead of a 'combinatorial' set ?

I think you want perms().

Re: Permutations in matlab

Midhun — Tue, 18 Aug 2009 08:53:01 -0400

> I think you want perms().

Thanks for your post. Infact, I was looking for a command in which I could specify the size of the subset ( not possible in ' perms(set) ' : all permutations would contain all the elements in the set. )

It is possible to do it in a roundabout way : take ' combntns(set,n) ' to get various combinations/subsets of size 'n' . For each of these rows , take perms() to get all possible permutations. Is it possible to do this using a single built-in command ?

Re: Permutations in matlab

arun — Tue, 18 Aug 2009 09:24:06 -0400

On Aug 18, 10:53 am, "Midhun " <midhunj...@gmail.com> wrote:
> > I think you want perms().
>
> Thanks for your post. Infact, I was looking for a command in which I could specify the size of the subset ( not possible in ' perms(set) ' : all permutations would contain all the elements in the set. )
>
> It is possible to do it in a roundabout way : take ' combntns(set,n) ' to get various combinations/subsets of size 'n' . For each of these rows , take perms() to get all possible permutations. Is it possible to do this using a single built-in command ?

yes there is no direct function for permutations, as there is 1 for
combinations. Probably because its not possible to store the
permutations for n>= 11 (documentation says it takes over 3GB).

however, for small amount of numbers you could do,

a = 1:4;

acn = nchoosek(a,3);
result = arrayfun(@(x) perm(acn(x,:)), 1:length(acn), 'uni', false);
result = cat(1,result{:});

to get the permutations.

best, arun.

Re: Permutations in matlab

Matt Fig — Tue, 18 Aug 2009 12:36:19 -0400

Re: Permutations in matlab

Midhun — Tue, 18 Aug 2009 14:10:23 -0400

Thanks a lot for the post...
- Midhun