Re: [Maxima-discuss] sign of permutation

[Daniel V. <dan...@ya...>]

 Hi Dimiter,
Thank you, that's exactly what I need.
Daniel Volinski

    En domingo, 7 de mayo de 2023, 00:07:07 GMT+3, Dimiter Prodanov <dim...@gm...> escribió:  
 
 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 oneshould 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

  _______________________________________________
Maxima-discuss mailing list
Max...@li...
https://lists.sourceforge.net/lists/listinfo/maxima-discuss