#19229: Bug in elliptic curve Galois Representation
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       Reporter:  cremona            |        Owner:
           Type:  defect             |       Status:  needs_work
       Priority:  major              |    Milestone:  sage-6.10
      Component:  elliptic curves    |   Resolution:
       Keywords:  Galois             |    Merged in:
  representations                    |    Reviewers:
        Authors:  John Cremona       |  Work issues:
Report Upstream:  N/A                |       Commit:
         Branch:  u/cremona/19229    |  62accc077ff28e2306364abaa60199846e292fdd
   Dependencies:                     |     Stopgaps:
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Comment (by cremona):

 Replying to [comment:18 jdemeyer]:
 > Just a question (not something to do for this ticket): did you ever
 consider computing the CM discriminant using the period lattice? If you
 have a sufficiently good (I guess this is the hard part) approximation to
 τ, you can compute its minimal polynomial A τ^2^ + B τ + C and from that
 the discriminant.

 Interesting idea.  Note that the existing code involves computing Hilbert
 Class Polynomials which does something similar.  We can get tau to high
 precision easily since there is such a fast convergence for the periods.
 But some care would be needed to make this rigorous.

 Improving the detection of CM would certainly be useful.

--
Ticket URL: <http://trac.sagemath.org/ticket/19229#comment:21>
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