Re: nfgaloisapply

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

[Paul van Wamelen:]
> According to the documentation nfgaloisapply is supposed to be able to
> take an ideal in idealprimedec form as an argument, but it does not
> seem to: [...]

According to source code, it looks like you're the first one to have actually
tried it... Here's a patch:

  Karim.

*** src/basemath/base1.c.orig	Wed Jan 20 17:09:33 1999
--- src/basemath/base1.c	Thu Feb  4 18:04:42 1999
***************
*** 897,909 ****
  galoisapply(GEN nf, GEN aut, GEN x)
  {
    long av=avma,tetpil,lx,j,N;
!   GEN p1,y,pol,unmod;
  
    nf=checknf(nf); pol=(GEN)nf[1];
    if (typ(aut)==t_POL) aut = gmodulcp(aut,pol);
    else
    {
!     if (typ(aut)!=t_POLMOD || !gegal((GEN)aut[1],pol) || gcmp0((GEN)aut[1]))
        err(talker,"incorrect galois automorphism in galoisapply");
    }
    switch(typ(x))
--- 897,909 ----
  galoisapply(GEN nf, GEN aut, GEN x)
  {
    long av=avma,tetpil,lx,j,N;
!   GEN p,p1,y,pol;
  
    nf=checknf(nf); pol=(GEN)nf[1];
    if (typ(aut)==t_POL) aut = gmodulcp(aut,pol);
    else
    {
!     if (typ(aut)!=t_POLMOD || !gegal((GEN)aut[1],pol))
        err(talker,"incorrect galois automorphism in galoisapply");
    }
    switch(typ(x))
***************
*** 930,944 ****
        }
        if (lg(x)!=6) err(typeer,"galoisapply");
        y=cgetg(6,t_VEC); y[1]=x[1]; y[3]=x[3]; y[4]=x[4];
!       unmod=gmodulsg(1,(GEN)x[1]);
!       p1=centerlift(gmul(unmod,algtobasis(nf,galoisapply(nf,aut,(GEN)x[2]))));
!       if (gcmp1((GEN)x[3]))
! 	if (ggval(subres(gmul((GEN)nf[7],p1),pol),(GEN)x[1]) > itos((GEN)x[4]))
! 	  p1[1] =  (signe(p1[1]) > 0)? lsub((GEN)p1[1],(GEN)x[1])
! 	                             : ladd((GEN)p1[1],(GEN)x[1]);
        y[2]=(long)p1;
!       p1=centerlift(gmul(unmod,algtobasis(nf,galoisapply(nf,aut,(GEN)x[5]))));
!       y[5]=(long)p1;
        tetpil=avma; return gerepile(av,tetpil,gcopy(y));
  
      case t_COL:
--- 930,943 ----
        }
        if (lg(x)!=6) err(typeer,"galoisapply");
        y=cgetg(6,t_VEC); y[1]=x[1]; y[3]=x[3]; y[4]=x[4];
!       p = (GEN)x[1];
!       p1=centermod(galoisapply(nf,aut,(GEN)x[2]), p);
!       if (is_pm1(x[3]))
! 	if (ggval(subres(gmul((GEN)nf[7],p1),pol), p) > itos((GEN)x[4]))
! 	  p1[1] =  (signe(p1[1]) > 0)? lsub((GEN)p1[1], p)
! 	                             : ladd((GEN)p1[1], p);
        y[2]=(long)p1;
!       y[5]=(long)centermod(galoisapply(nf,aut,(GEN)x[5]), p);
        tetpil=avma; return gerepile(av,tetpil,gcopy(y));
  
      case t_COL:
--
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
--
PARI/GP Home Page: http://hasse.mathematik.tu-muenchen.de/ntsw/pari/