Karim Belabas on Mon, 10 Jan 2005 13:35:22 +0100

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Re: Gaussian Integer factorisation at right angles

* Phil Carmody [2005-01-06 17:31]:
> Is there any reason why things should get rotated by 90 degrees?
> (18:16) gp > factorback(factor(17+0*I))

The same one as for

(14:16) gp > factorback(factor(-x))
%1 = x

(or worse, factor(x*y) ... ).

factor() is a little inconsistent in that it factors up to units in the
chosen UFD, _except_ if the latter hapens to be Z, in which case
annoying factors (-1)^1 crop up.

I would be very much in favor of factoring consistently up to units
(choosing some well documented normal form for irreducibles). Then
perhaps adding a new function (or flag...) that returns a factorization
_and_ the missing unit.


Karim Belabas                     Tel: (+33) (0)1 69 15 57 48
Dep. de Mathematiques, Bat. 425   Fax: (+33) (0)1 69 15 60 19
Universite Paris-Sud              http://www.math.u-psud.fr/~belabas/
F-91405 Orsay (France)            http://pari.math.u-bordeaux.fr/  [PARI/GP]