Karim BELABAS on Tue, 29 Jul 2003 13:23:20 +0200 (MEST) |
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Re: polgalois() bug |
On Sat, 19 Jul 2003, Igor Schein wrote: > On Fri, Jul 04, 2003 at 09:47:08PM +0200, Karim BELABAS wrote: > > On Thu, 26 Jun 2003, Igor Schein wrote: > > > some time ago Galois group notation slightly changed. It's probably > > > due to this fact that I am seeing this incorrect result in CVS and > > > several previous alpha releases: > > > > > > ? polgalois(x^6-9*x^4+18*x^2-6)==polgalois(x^6-3*x^4+3) > > > 1 > > > > Indeed a typo [ confusion between group order and degree of defining > > polynomial ]. > > Still problems: > > ? polgalois(x^6+3) > [6, -1, 1] > > This is wrong, should be [6, -1, 2] Background info: internally the polgalois routine identifies a group using the "standard" numbering of transitive subgroups of S_n. The internal output is actually [n, k], where k is this standard number. For backward compatibility reasons, this is translated to [ n, s, k' ], where s is the group signature and k' is an ad hoc identifier (almost always equal to 1) if the polynomial degree is less than 7 [ see the polgalois() doc and new_galois_format default for further info ]. The translation was done improperly... Should be OK now. Karim. -- 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 http://www.math.u-psud.fr/~belabas/ F-91405 Orsay (France) http://www.parigp-home.de/ [PARI/GP]