Re: PARI/GP vecsort/versearch and Mod()

[Karim Belabas <Karim.Belabas@u-bordeaux.fr>]

* hermann@stamm-wilbrandt.de [2025-11-15 19:12]:
> On 2025-11-15 17:49, Bill Allombert wrote:
[...]
> > F4 = { [[Mod(0,2),Mod(0,2);  \\ 0
> >         Mod(0,2),Mod(0,2)],
> >        [Mod(1,2),Mod(0,2);   \\ 1
> >         Mod(0,2),Mod(1,2)],
> >        [Mod(0,2),Mod(1,2);   \\ a
> >         Mod(1,2),Mod(1,2)],
> >        [Mod(1,2),Mod(1,2);   \\ b
> >         Mod(1,2),Mod(0,2)]]; }
[...]

For readability, I would write

F4 = { [[0,0;   \\ 0
         0,0],
        [1,0;   \\ 1
         0,1],
        [0,1;   \\ a
         1,1],
        [1,1;   \\ b
         1,0]] * Mod(1,2); }

or

F4 = { [[0,0; 0,0],  \\ 0
        [1,0; 0,1],  \\ 1
        [0,1; 1,1],  \\ a
        [1,1; 1,0]]  \\ b
        * Mod(1,2); }

or, in two steps, F4 = ... (over Z) then F4 *= Mod(1, 2). Etc.

Cheers,

    K.B.

P.S. The hackish recursive F4 = Mod(F4, 2) also works ... and is marginally
faster than multiplying by Mod(1, 2).

-- 
Pr. Karim Belabas, U. Bordeaux, Vice-président en charge du Numérique
Institut de Mathématiques de Bordeaux UMR 5251 - (+33) 05 40 00 29 77
http://www.math.u-bordeaux.fr/~kbelabas/