#11683: ell_curve_isogeny initialization
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Reporter: saraedum | Owner: cremona
Type: enhancement | Status: new
Priority: minor | Milestone: sage-4.7.2
Component: elliptic curves | Keywords: startup, initialization
Work_issues: | Upstream: N/A
Reviewer: | Author: Julian Rueth
Merged: | Dependencies:
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Comment(by was):
The claimed code for pre-computing Psi does not work at all. Even
changing the monic() part to do what is intended totally fails to give the
claimed result. Some remarks:
1. This code was originally introduced by John Cremona and his undergrad
student in #6887, and given a positive review by Christian Wuthrich. At
that point the comment about how to compute the polys should have been
changed to a doctest. Oops.
2. One could not use the examples (if they worked) to compute more
values of Psi, since they depend on the Fricke module table, which is only
computed up to ell=13.
3. The definition and meaning of Psi should be documented. I spent
maybe 30 minutes wondering and searching, and I still am not completely
sure *precisely* what Psi even is...
So I suggest removing these broken examples from the second patch, then
setting this patch as "needs review". I'll ping John Cremona and request
that he add an appropriate doctest illustrating how to compute Psi, and
documenting what it is. I'm betting this will be really trivial for him
to do. (I'm surprised it wasn't for me, because I just did a lot with
explicit isogenies for an REU this summer... but it wasn't.)
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/11683#comment:7>
Sage <http://www.sagemath.org>
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