Re: relative number fields

[Karim BELABAS <Karim.Belabas@math.u-psud.fr>]

[Annegret Weng:]
> I am using the Pari-Library and I would like to create a relative number
> field by using the function rnfinitalg. But I always get a run time error.
>  
> First I created a number field nf with the function nfinit0 and with a
> polynomial in # (say for example #^2+5). Then I created an object of type
> polmod (e.g. 3*#+2). Finally I called rnfinitalg with the parameters nf,
> a polynomial in x having as coefficients objects of type polmod and
> prec=3. At the end I got the error message "type mod I forbidden in gmod".
> What did I do wrong?

MAXVARN (#) is better left to PARI internals [ this should be stressed in the
manual, and checked in the library functions ].

  long prec = DEFAULTPREC;
  long vx = 0;
  long vy = fetch_user_var("y"); /* > vx */
  GEN x = polx[vx];
  GEN y = polx[vy];
  GEN pol = gaddsg(5, gsqr(y));
  GEN nf = nfinit0(pol, 0, prec);
  GEN a = gmodulcp( gaddsg(2, gmulsg(3,y)), pol );

  GEN polrel = gsub(gsqr(x), a);  /* for instance... */
  GEN relnf = rnfinitalg(nf, polrel, prec);

[ if you need temporary variables, it's safer to use fetch_var()/delete_var() ]

Cheers,

  Karim.
__
Karim Belabas                    email: Karim.Belabas@math.u-psud.fr
Dep. de Mathematiques, Bat. 425
Universite Paris-Sud             Tel: (00 33) 1 69 15 57 48
F-91405 Orsay (France)           Fax: (00 33) 1 69 15 60 19
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