Karim BELABAS on Wed, 6 Nov 2002 16:22:23 +0100 (MET) |
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Re: nfinit(,4) |
On Tue, 5 Nov 2002, Igor Schein wrote: [ to me, apparently not to the list, I'm repeating the relevant bits ] > On Wed, Nov 06, 2002 at 01:08:32AM +0100, Karim BELABAS wrote: > > On Tue, 5 Nov 2002, Igor Schein wrote: > > > nfinit(,4) is not doing partial polred like it's supposed to according > > > to the documentation. > > > > Err, could you be a bit more specific ? > > > > I hit a SEGV in nfinit(x^2-4*3, 4), due to a stupid typo which I fixed. But > > besides that, I see nothing wrong. > > setrand(1); > p=x^24+62*x^12+1; > for(k=1,3,p=poltschirnhaus(p)); > \g5 > nfinit(p,4); > > You can see that it's trying to completely factor the discriminant. However, > > ? ?nfinit > [snip] > 4: as 2 but use a partial polred; The documentation is too vague: it means "partial polred" in the sense of "look only at the first vectors in the reduced basis" (as opposed to _all_ basis vectors), not "use a partial factorization of the discriminant". This is IMHO a confusing and completely useless feature of nfinit: * you get much more control using polredabs / polred and their specific flags. * the time-critical operation is the discriminant factorization, not the computation of a few characteristic polynomials. So your interpretation is in fact the logical one. I'd rather "undocument" nfinit flags 4 and 5 (warning that these flags are deprecated). Karim. -- Karim Belabas Tel: (+33) (0)1 69 15 57 48 Dép. de Mathematiques, Bat. 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/