Re: vector of t_FRAC questions

[Bill Allombert <Bill.Allombert@math.u-bordeaux.fr>]

On Mon, Jul 15, 2024 at 10:01:47PM +0200, hermann@stamm-wilbrandt.de wrote:
> I convert 3-dimensional vector or GMP mpq_t rational numbers from
> CGAL function get_build_direction() to GP this way:
> 
> https://github.com/Hermann-SW/cgal4gp/blob/main/cgal4gp.cpp#L107-L123
> 
> extern "C"
> GEN
> get_build_direction() {
>     assert(_simplex != NULL);
>     _Vector_3 _dir = _simplex->get_build_direction();
> 
>     return mkvec3(
>                mkfrac(
>                    mpz2GEN(_dir[0].num.mpz()),
>                    mpz2GEN(_dir[0].den.mpz())),
>                mkfrac(
>                    mpz2GEN(_dir[1].num.mpz()),
>                    mpz2GEN(_dir[1].den.mpz())),
>                mkfrac(
>                    mpz2GEN(_dir[2].num.mpz()),
>                    mpz2GEN(_dir[2].den.mpz())));
> }
> 
> That works nicely, but I get denominators of 1:

You are not supposed to use mkfrac with a denominator of 1,
since you already have a t_INT.

Instead you can use

GEN
mkfrac_or_int(GEN a, GEN b)
{
  return equali1(b) ? a: mkfrac(a,b);
}

Cheers,
Bill