Re: [Maxima-discuss] sign of permutation

[Dimiter P. <dim...@gm...>]

Here is what I wrote for the clifford packages

permsign(arr):=block([k:0, len, ret:0 ] ,
     mode_declare([k, len], fixnum),
     if not listp(arr) then return (false),
     len:length(arr),
     for i:1 thru len do (
          if not mapatom(arr[i]) then ret:nil,
          for j:i+1 thru len do
              if ordergreatp(arr[i], arr[j]) then k:k+1
     ),
     if ret#nil then
           if evenp(k)  then 1 else -1
     else 0
);

best regards,

Dimiter

On Sat, May 6, 2023 at 10:00 AM Daniel Volinski via Maxima-discuss <
max...@li...> wrote:

> Hi Jaime,
>
> Thank you for the input.
> However, this is not what I need.
>
> My original intention was to symmetrize or anti-symmetrize tensors with
> abstract indices.
> For the symmetrization there is no problem because you sum all the
> permutations.
> But for the anti-symmetrization you need to sum all the permutations but
> each one
> should be multiplied by the sign (or parity) of the permutation.
>
> perm_parity([λ,σ,μ]) issues an error: "argument should be a permutation".
>
> Thanks,
>
> Daniel Volinski
>
>
> En viernes, 5 de mayo de 2023, 21:23:23 GMT+3, Jaime Villate <
> vi...@fe...> escribió:
>
>
> On 05/05/23 18:24, Daniel Volinski via Maxima-discuss wrote:
> > Is there a command in Maxima the calculates the sign of a permutation?
> >
> > Given a base permutation (a list) and a test permutation (a list) of
> > the same elements,
> > I would l like a command to calculate the number of switches needed to
> > go from one
> > to the other or (alternatively) whether this number is odd or even.
> >
> Hello Daniel,
>
> Function perm_parity, from additional package combinatorics, will give 0
> if the permutation is even or 1 if it is odd.
>
> Regards,
>
> Jaime
>
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