#5928: [with patch, positive review] binary operations on factorisations should
coerce factors into a common universe
---------------------------+------------------------------------------------
Reporter: AlexGhitza | Owner: AlexGhitza
Type: defect | Status: assigned
Priority: major | Milestone: sage-4.0
Component: factorization | Keywords: multiplication factorization coercion
---------------------------+------------------------------------------------
Comment(by cremona):
This patch looks good, applies to 3.4.2.alpha0 and tests in sage/structure
pass as well as those in sage/rings/*.py (I did not go into
subdirectories).
I was a little disappointed by this:
{{{
sage: R.<x> = ZZ[]
sage: S.<y> = QQ[]
sage: f = x^2-1
sage: g = y^3-1
sage: f.factor()
(x - 1) * (x + 1)
sage: g.factor()
(y - 1) * (y^2 + y + 1)
sage: f.factor() * g.factor()
(1) * (y - 1) * (x - 1) * (x + 1) * (y^2 + y + 1)
sage: (f.factor() * g.factor()).universe()
Category of objects
}}}
and in fact coercion is not clever enough to allow x*y here. but it does
work if you do
{{{
sage: S.<x> = QQ[]
sage: y=S.gen(0)
sage: g = y^3-1
sage: f.factor() * g.factor()
(x + 1) * (x - 1)^2 * (x^2 + x + 1)
}}}
-- i.e. you have to define the two rings with the same name of the
variable even if you use a different name for input. Weird, but it is not
going to stop this patch!
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/5928#comment:2>
Sage <http://sagemath.org/>
Sage - Open Source Mathematical Software: Building the Car Instead of
Reinventing the Wheel
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