#16456: Bug in descend_to method for elliptic curves
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Reporter: cremona | Owner: cremona
Type: defect | Status: needs_review
Priority: major | Milestone: sage-6.3
Component: elliptic curves | Resolution:
Keywords: elliptic curve | Merged in:
base change | Reviewers: Peter Bruin
Authors: John Cremona | Work issues:
Report Upstream: N/A | Commit:
Branch: | e0a13b3931a2c0d0360a57a36a841cde96e00355
u/cremona/16456-descend_to_bug | Stopgaps:
Dependencies: #16708 |
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Changes (by cremona):
* status: needs_work => needs_review
Comment:
...done. I added an optional parameter "orders" to the selmer_group
method, default False gives the old behavious, if True also outputs a list
of the orders of the generators, which are all equal to m when m is prime,
but not necesarily otherwise. Added doctests for this. Now the iterator
uses this instead of the old formula, which was wrong. I thought that
this was simpler than trying to recover the orders from the list of
generators, since it is information we have to hand when constructing the
list of generators.
For consistency I did the same for the special versions over QQ, though
the bug did not apply here. At the same time I noticed that over QQ when
-1 is a generator it was put last while over number fields the units are
always first, so I changed that (and the associated doctests) too.
Note that this change will be superceded after #16496 when there is a
proper class for these Selmer groups. And also that the correctness of
the current selmer_group function relies on the direct product fact
alluded to in earlier comments!
--
Ticket URL: <http://trac.sagemath.org/ticket/16456#comment:24>
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