#15364: Introduce factor_or_zero into global namespace
-------------------------------------+-------------------------------------
Reporter: zabrocki | Owner:
Type: enhancement | Status: needs_review
Priority: minor | Milestone: sage-5.13
Component: factorization | Resolution:
Keywords: | Merged in:
Authors: Mike Zabrocki | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
public/ticket/15364-factor_or_zero | 16e72e7244e735bcbfc3cc4bf8effb2ea7fae330
Dependencies: | Stopgaps:
-------------------------------------+-------------------------------------
Comment (by darij):
Nice, but incomplete, since it only works with integers:
{{{
sage: P = PolynomialRing(QQ, 'x')
sage: P.inject_variables()
Defining x
sage: factor(P.zero())
---------------------------------------------------------------------------
ValueError Traceback (most recent call
last)
<ipython-input-3-81007cf0bccf> in <module>()
----> 1 factor(P.zero())
/home/darij/gitsage/sage-5.13.beta1/local/lib/python2.7/site-
packages/sage/rings/arith.pyc in factor(n, proof, int_, algorithm,
verbose, **kwds)
2470 # e.g. n = x**2 + y**2 + 2*x*y
2471 try:
-> 2472 return n.factor(proof=proof, **kwds)
2473 except AttributeError:
2474 raise TypeError, "unable to factor n"
/home/darij/gitsage/sage-5.13.beta1/local/lib/python2.7/site-
packages/sage/rings/polynomial/polynomial_element.so in
sage.rings.polynomial.polynomial_element.Polynomial.factor
(sage/rings/polynomial/polynomial_element.c:24652)()
ValueError: factorization of 0 not defined. See factor_or_zero to return
0.
}}}
Also, please be aware that `Factorization` objects (which is what `factor`
normally returns) have some methods which should probably be imitated by
the `0` object, or else the can is merely being kicked down the road. For
instance, the `value` method of a factorization multiplies it back
together, and it is way more useful than it looks from that description:
{{{
sage: Q = FractionField(P)
sage: Q(14*x) / Q(28*(x+1))
14*x/(28*x + 28)
sage: factor(_).value()
1/2*x/(x + 1)
}}}
0, of course, doesn't have that attribute:
{{{
sage: 0.value()
---------------------------------------------------------------------------
AttributeError Traceback (most recent call
last)
<ipython-input-4-65708360c0e8> in <module>()
----> 1 Integer(0).value()
/home/darij/gitsage/sage-5.13.beta1/local/lib/python2.7/site-
packages/sage/structure/element.so in
sage.structure.element.Element.__getattr__
(sage/structure/element.c:3873)()
/home/darij/gitsage/sage-5.13.beta1/local/lib/python2.7/site-
packages/sage/structure/misc.so in
sage.structure.misc.getattr_from_other_class
(sage/structure/misc.c:1696)()
AttributeError: 'sage.rings.integer.Integer' object has no attribute
'value'
}}}
--
Ticket URL: <http://trac.sagemath.org/ticket/15364#comment:7>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
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