Further to my earlier post, a search for "def factor(self," in the
Sage library reveals that there are a lot of instances where the
factoring method supports various arguments. Thus, at the very least,
I think the fraction field implementation should allow further
arguments, too, and simply forward them, that is, the code should
change from
def factor(self):
return self.numerator().factor()/self.denominator().factor()
to
def factor(self, *args)
return self.numerator().factor(args)/self.denominator().factor
(args)
Moreover, I guess the parameter "proof" should be documented in the
method "factor" for multivariate polynomials.
Sebastian
On Jan 7, 4:11 pm, Sebastian Pancratz <s...@pancratz.org> wrote:
> Dear John,
>
> I haven't written any of the code involved, so I am not absolutely
> sure about this, but after looking at the code for a few minutes, I
> think the following is the case:
>
> The "FractionFieldElement" objects have a method "factor", but this
> takes no arguments other than "self". This explains the error message
> in the second case you describe. On the other hand, the
> "MPolynomial_libsingular" objects provide the method "factor(self,
> proof=True)". Here, however, the parameter "proof" is only used to
> prevent certain inputs (with the option "proof=True" set) from being
> passed to Singular, presumably(?) in cases when Singular's results
> might not be reliable. There appears to be no further use of the
> parameter.
>
> I think this is something that ought to fixed. (N.B. I don't think I
> know enough about what kind of factoring methods rings in Sage
> typically offer.) If rings often offer further arguments to the
> method "factor", then I think the method "factor" for
> FractionFieldElement objects should be modified to allow the same
> arguments. On the other hand, if "MPolynomial_libsingular" is the
> only case where "factor" takes further arguments, perhaps the second
> argument ought to be removed?
>
> Sebastian
>
> On Jan 7, 3:32 pm, John Cremona <john.crem...@gmail.com> wrote:
>
> > I define a rational function in two variables over a finite field:
>
> > {{{
> > sage: R.<x,y> = GF(2)[]
> > sage: f = x*y/(x+y)
> > sage: f.parent()
> > Fraction Field of Multivariate Polynomial Ring in x, y over Finite
> > Field of size 2
>
> > }}}
>
> > I try to factor it, and get this error:
>
> > {{{
> > sage: f.factor()
> > ---------------------------------------------------------------------------
> > NotImplementedError Traceback (most recent call last)
>
> > /home/masgaj/.sage/temp/host_56_150/17587/_home_masgaj__sage_init_sage_0.py
> > in <module>()
>
> > /local/jec/sage-4.3.rc0/local/lib/python2.6/site-packages/sage/rings/fraction_field_element.so
> > in sage.rings.fraction_field_element.FractionFieldElement.factor
> > (sage/rings/fraction_field_element.c:2972)()
>
> > /local/jec/sage-4.3.rc0/local/lib/python2.6/site-packages/sage/rings/polynomial/multi_polynomial_libsingular.so
> > in
> > sage.rings.polynomial.multi_polynomial_libsingular.MPolynomial_libsingular.factor
> > (sage/rings/polynomial/multi_polynomial_libsingular.cpp:22701)()
>
> > NotImplementedError: proof = True factorization not implemented. Call
> > factor with proof=False.
>
> > }}}
>
> > So I do what I am told, but:
>
> > {{{
> > sage: f.factor(proof=False)
> > ---------------------------------------------------------------------------
> > TypeError Traceback (most recent call last)
>
> > /home/masgaj/.sage/temp/host_56_150/17587/_home_masgaj__sage_init_sage_0.py
> > in <module>()
>
> > TypeError: factor() takes no keyword arguments
>
> > }}}
>
> > Worth a ticket, I think?
>
> > Also, does anyone know what the proof parameter for this sort of
> > factorization actually means?
>
> > John
>
>
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