#15299: Incorrect results for analytic Sha due to low precision
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       Reporter:  jdemeyer         |        Owner:
           Type:  defect           |       Status:  needs_review
       Priority:  major            |    Milestone:  sage-5.13
      Component:  elliptic curves  |   Resolution:
       Keywords:                   |    Merged in:
        Authors:  Jeroen Demeyer   |    Reviewers:
Report Upstream:  N/A              |  Work issues:
         Branch:                   |       Commit:
   Dependencies:                   |     Stopgaps:
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Comment (by pbruin):

 Replying to [comment:22 cremona]:
 > You can go one step further thanks to Gross-Zagier:  if the parity is
 odd and L'(1) looks zero then you can prove it, since if in fact L'(1)!=0
 then the curve would have rank 1, but you can disprove that by finding
 three (or oeven only 2) independent points.
 That is true (in fact I seem to remember learning this from the talk you
 linked to).  However, it does require you to search for points; there
 seems to be no "analytic" way of proving that L'(1) = 0 by computing it to
 finite precision, like the `L1_vanishes()` function.

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Ticket URL: <http://trac.sagemath.org/ticket/15299#comment:23>
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