#11685: Pari finite field extension: element created by list not recognised as
zero
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Reporter: johanbosman | Owner: AlexGhitza
Type: defect | Status: needs_work
Priority: major | Milestone: sage-4.7.2
Component: algebra | Keywords: finite fields, pari
Work_issues: | Upstream: N/A
Reviewer: Simon King, Johan Bosman | Author: Johan Bosman, Jeroen
Demeyer
Merged: | Dependencies:
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Comment(by SimonKing):
Replying to [comment:22 jdemeyer]:
> I think that the fact that your example works for the first patch is an
unintentional side-effect and not really an intended feature.
Intended or not doesn't matter. It is a feature, I think.
> I believe that I am fixing much more than what the ticket requires, ...
Indeed it does, namely:
{{{
sage: k.<x> = GF(3^11)
sage: k([ k(0),k(1) ])
x
sage: k([0,1/2])
2
sage: R.<y> = PolynomialRing(k)
sage: k([ R(0),R(1) ])
x
}}}
It a strength of your patch that the examples above work (they wouldn't,
with the other patch).
Do you see a way to make ''both'' work?
I wouldn't say that your patch is simpler, because you first convert into
a list of prime field elements and then convert into pari; a double
conversion, so it seems to me, tends to be fragile.
I mean, the only problem with
`k([k([0])._FiniteField_ext_pariElement__value])` in your patch is the
fact that the pari value (which, after all, is zero) can not be converted
into the zero of a finite field. There could be a work around, such as
{{{
value = [GFp(c) for c in value if c else GFp.zero_element()]
}}}
Concerning speed, one should test whether `k([])` is the only case in
which your patch is slower. Since you have a special case for `k([])`
anyway, it would be perfectly fine to have a short-cut, such as
{{{
if not value: # or value==[], if that's faster
self.__value = (pari(0) *
parent._pari_one()).Mod(parent._pari_modulus())
}}}
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/11685#comment:23>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
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