Opened 11 years ago
Closed 10 years ago
#6455 closed defect (fixed)
[with patch, with positive review] Bug in twisting for p_primary_bound on Tate-Shafarevich groups
Reported by: | wuthrich | Owned by: | |
---|---|---|---|
Priority: | minor | Milestone: | sage-4.2 |
Component: | elliptic curves | Keywords: | Tate Sharafevich group, Elliptic curves |
Cc: | was | Merged in: | sage-4.2.alpha1 |
Authors: | Chris Wuthrich | Reviewers: | John Cremona |
Report Upstream: | Work issues: | ||
Branch: | Commit: | ||
Dependencies: | Stopgaps: |
Description
William Stein found a bug in p_primary_part
, namely
sage: E = EllipticCurve([-19,34]); E.cremona_label() # y^2 = x^3 - 19*x + 34 '944e1' sage: S = E.sha(); S Shafarevich-Tate group for the Elliptic Curve defined by y^2 = x^3 - 19*x + 34 over Rational Field sage: E.ap(5) -3 sage: factor(944) 2^4 * 59 sage: S.an_padic(5) Traceback (most recent call last): ... ValueError: can not twist a curve of conductor (=472) by the quadratic twist (=-4).
The problem is at 2 and 3, we have to check if we are allowed to twist.
And John Cremona suggested
Is it possible to add a doctest illustrating the suggestion to "try an_padic instead"? That would be useful for the reference manual.
Attachments (1)
Change History (9)
comment:1 Changed 11 years ago by
- Component changed from number theory to elliptic curves
- Owner changed from was to davidloeffler
comment:2 Changed 11 years ago by
- Cc was added
- Summary changed from Bug in twisting for p_primary_bound on Tate-Shafarevich groups to [with patch, needs review] Bug in twisting for p_primary_bound on Tate-Shafarevich groups
Changed 11 years ago by
comment:3 Changed 11 years ago by
- Summary changed from [with patch, needs review] Bug in twisting for p_primary_bound on Tate-Shafarevich groups to [with patch, with positive review] Bug in twisting for p_primary_bound on Tate-Shafarevich groups
Patch applies fine to 4.1.1, and tests run ok. The code looks ok to me too. I'm not quite expert enough to be 100% confident, but enough to pass this!
comment:4 Changed 11 years ago by
- Reviewers set to John Cremona
comment:5 Changed 10 years ago by
- Status changed from new to needs_review
comment:6 Changed 10 years ago by
- Status changed from needs_review to positive_review
comment:7 Changed 10 years ago by
- Owner changed from davidloeffler to (none)
comment:8 Changed 10 years ago by
- Merged in set to sage-4.2.alpha1
- Resolution set to fixed
- Status changed from positive_review to closed
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I believe that the patch chooses now the correct twist.
William : could you use it for the table, before it goes in ? so that I am sure that there are no further problems with it. I have tested it only on a few examples.