Re: bnfisnorm() broken again

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

On Mon, 9 Sep 2002, Igor Schein wrote:
> On Tue, Sep 10, 2002 at 03:38:40AM +0200, Karim BELABAS wrote:
> > On Mon, 9 Sep 2002, Igor Schein wrote:
> > > ? bnfisnorm(bnfinit(x^3-2),5)
> > >   ***   division by zero in dvmdii
> >
> > A few oversights in the new implementation of rnfisnorm in the non-Galois
> > case [had forgotten to test it over Q except for quadratic fields...]
> >
> > Fixed.
>
> How about this:
>
> ? bnfisnorm(bnfinit(x^3-x-1),13)
>   ***   incorrect type in lift.

Right, the special case where the solution is trivial (rnfisnorm(x) --> [1,x]).
The code over Q in bnfisnorm() did not handle it properly.

Note: in the CVS code, bnfisnorm is quite useless  [ it used to be justified
by the weird input format for rnfisnorm ].

  N = rnfisnorminit(y, x^3-x-1); [ or rnfisnorminit(y, bnf) if you wish ]
  rnfisnorm(N, 13);

works just as well. And is faster since bnfisnorm is a trivial wrapper for
the above code anyway [ N is (a little) costly to compute, esp. if you give
bnfisnorm a bnf which is Galois over Q, and do not use the right flag to
mention that fact ].

    Karim.
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Karim Belabas                    Tel: (+33) (0)1 69 15 57 48
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