[with patch, with positive review] Bug in twisting for p_primary_bound on TateShafarevich groups
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
ShafarevichTate 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.
Change History (9)
Component: 
number theory →
elliptic curves

Owner: 
changed from William Stein to David Loeffler

Cc: 
William Stein added

Summary: 
Bug in twisting for p_primary_bound on TateShafarevich groups →
[with patch, needs review] Bug in twisting for p_primary_bound on TateShafarevich groups

Summary: 
[with patch, needs review] Bug in twisting for p_primary_bound on TateShafarevich groups →
[with patch, with positive review] Bug in twisting for p_primary_bound on TateShafarevich groups

Authors: 
→ Chris Wuthrich

Reviewers: 
→ John Cremona

Status: 
new →
needs_review

Status: 
needs_review →
positive_review

Owner: 
David Loeffler deleted

Merged in: 
→ sage4.2.alpha1

Resolution: 
→ fixed

Status: 
positive_review →
closed

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.