[Jprogramming] inverse permutation vector

[Roger Hui]

   p=: ?~23
   /:p
0 20 3 7 6 19 11 12 8 10 1 15 2 5 21 14 9 4 13 18 16 17 22
   |.&.>&.C. p
0 20 3 7 6 19 11 12 8 10 1 15 2 5 21 14 9 4 13 18 16 17 22



----- Original Message -----
From: Roger Hui <rhui000 at shaw.ca>
Date: Sunday, September 9, 2007 9:06
Subject: Re: [Jprogramming] inverse permutation vector
To: Programming forum <programming at jsoftware.com>

> There is an isomorphism between integer permutation vectors
> and boolean permutation matrices under {= and i."1&1 .
> Therefore:
> 
> (/:p) -: |:&.(({=) :. (i."1&1)) p
> 
> http://www.jsoftware.com/jwiki/Essays/Symmetries_of_the_Square
> 
> 
> 
> ----- Original Message -----
> From: Oleg Kobchenko <olegykj at yahoo.com>
> Date: Sunday, September 9, 2007 0:16
> Subject: Re: [Jprogramming] inverse permutation vector
> To: Programming forum <programming at jsoftware.com>
> 
> > Also
> > 
> >    (i. i.@#) p
> > 0 20 3 7 6 19 11 12 8 10 1 15 2 5 21 14 9 4 13 18 16 17 22
> > 
> > Variation
> > 
> >    i.@#@]`]`]}~ p
> > 0 20 3 7 6 19 11 12 8 10 1 15 2 5 21 14 9 4 13 18 16 17 22
> > 
> > 
> > --- Roger Hui <rhui000 at shaw.ca> wrote:
> > 
> > > Another solution.  Both are well-known in APL circles.
> > > 
> > >    ] p=: ?~23
> > > 0 10 12 2 17 13 4 3 8 16 9 6 7 18 15 11 20 21 19 5 1 14 22
> > >    /: p
> > > 0 20 3 7 6 19 11 12 8 10 1 15 2 5 21 14 9 4 13 18 16 17 22
> > >    p}~i.#p
> > > 0 20 3 7 6 19 11 12 8 10 1 15 2 5 21 14 9 4 13 18 16 17 22
> > > 
> > > 
> > > 
> > > ----- Original Message -----
> > > From: bill lam <bbill.lam at gmail.com>
> > > Date: Saturday, September 8, 2007 20:01
> > > Subject: Re: [Jprogramming] inverse permutation vector
> > > To: Programming forum <programming at jsoftware.com>
> > > 
> > > > Raul Miller wrote:
> > > > > ipv=: /: pv
> > > > 
> > > > Thank you, I didn't realize that is so simple.