#11271: there is a serious bug in the documentation or code for is_surjective
for
Galois representations attached to elliptic curves
-------------------------------------+-------------------------------------
Reporter: was | Owner: cremona
Type: defect | Status: needs_review
Priority: critical | Milestone: sage-6.1
Component: elliptic curves | Resolution:
Keywords: | Merged in:
Authors: Chris Wuthrich | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
u/wuthrich/ticket/11271 | 4c57ec058d7033b233b60b35993fb1e55d6982d1
Dependencies: | Stopgaps:
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Comment (by cremona):
Replying to [comment:9 wuthrich]:
> I am certainly not angry, but thankful for your work.
>
> I don't understand 4). Being reducible for the Galois module E[p] is
equivalent to E having an isogeny defined over Q and so the answer is ok
in all cases, including cm and including 27a. Did you get confused with
non_surjective. There is should return [0] as documented.
Sorry, just a stupid mistake.
>
> 1) There is already #11905 on the splitting field. I agree that division
field could become a visible function. I opened a ticket on it : #15610.
OK, good.
>
> 3) Yes, I will do that. Is there a python rule about this in general?
I don't know of a rule, but one has to be careful. Similarly, elliptic
curves used to cache their a-invariants as a list and return them which
meant that they could be changed; to avoid that the invariants are cached
as a tuple which is immutable. But here it is the curve itself which is
being cached. I also realise that the same problem exists with, for
example, the period lattice of an elliptic curve. Sometimes people use a
double underscore attribute name (e.g. EllipticCurveTorsionSubgroup has an
attribute {{{__E}}} to store its curve, but that in itswelf does not stop
it being maliciously (or by mistake) changed.
We may need to consult experts on this.
>
> 5) Oh, that is a left over from a further change towards #11270. Sorry.
OK, it is fairly harmless but if #11270 is slatted then perhaps it is
worth changing here.
>
> I'd proof-read the documentation as well as I can.
OK, thanks -- sorry I was lazy and did not give line numbers.
----
New commits:
||[[http://git.sagemath.org/sage.git/commit/?id=4c57ec0|4c57ec0]]||{{{Trac
#11271: making the curve inaccessible + documentation}}}||
--
Ticket URL: <http://trac.sagemath.org/ticket/11271#comment:12>
Sage <http://www.sagemath.org>
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