Karim BELABAS on Wed, 20 Nov 2002 20:10:21 +0100 (MET)

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Re: Bug rnfconductor

On Wed, 20 Nov 2002, Bill Allombert wrote:
> On Sat, Nov 16, 2002 at 01:49:41PM +0100, Karim BELABAS wrote:
> > I have a backward compatibility problem here: the format is
> >  * undocumented (it is documented in the source code)
> >  * needed for a single routine: ideallog
> >  * painful to use as it stands: lists of lists of lists of ..., where you
> > access different layers at the same time depending on the information you
> > need.
> >  * lacking needed data [nfmodprinit, exponent of (O_K/P^e)^* for each P | f ]
> > that I have to recompute each time I use it. When the modulus has no huge
> > prime divisors, this recomputation dominates computation time in ideallog :-(.
> Since nfinit format has already changed and bnrinit contains the nfinit data,
> it looks like the new bnrinit format is already incompatible.
> Since we have already changed the documented output, why not change
> the undocumented one ? And maybe document the new one in the process ?

I have also already changed the 'bnf' and 'small bnf' formats, but in a
partially backward compatible way:

* programs making low-level accesses to the (previously undocumented)
structure members are indeed broken [I don't think these exist, besides mine]

* elements and ideals from gp-2.0 stored in coordinate form are indeed broken
(default basis changed).


* gp-2.2 is able to use legacy nf, bnf and sbnf from previous versions in any
high level function. ( I left some amount of inefficient compatibility code,
hanging around for this purpose, perhaps 500 lines altogether )

My proposed change breaks even this for idealstar() and bnrinit() formats
[ both of which have no reason to be stored in the first place in my opinion ]

I am afraid you are quite right about the documentation bit. But this will
eat a lot of my time, of which I have currently very little to spare. Do not
expect it in the near future.


P.S: Btw, I have updated my PARI pages at


Feedback welcome.
Karim Belabas                    Tel: (+33) (0)1 69 15 57 48
Dép. de Mathématiques, Bât. 425  Fax: (+33) (0)1 69 15 60 19
Université Paris-Sud             Email: Karim.Belabas@math.u-psud.fr
F-91405 Orsay (France)           http://www.math.u-psud.fr/~belabas/
PARI/GP Home Page: http://www.parigp-home.de/