#6384: elliptic curve -- isogeny function seems completely totally broken in
first
example I try
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Reporter: was | Owner: tbd
Type: defect | Status: new
Priority: major | Milestone: sage-4.1
Component: algebra | Keywords:
Reviewer: | Author:
Merged: |
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First the docstring for E.isogeny? has a typo
{{{
(defaul:None)
}}}
Note the missing t.
Next, I tried taking the elliptic curve 11a and one 5-torsion point P on
it and trying to make the isogeny {{{E --> E/<P>}}}. It seems that the
result is a '''total disaster in every imaginable way'''.
{{{
sage: E = EllipticCurve('11a'); P = E.torsion_subgroup().gens()[0]; P
(5 : 5 : 1)
sage: phi = E.isogeny([P]); phi
Isogeny of degree 1 from Elliptic Curve defined by y^2 + y = x^3 - x^2 -
10*x - 20 over Rational Field to Elliptic Curve defined by y^2 + y = x^3 -
x^2 - 560*x - 4277 over Rational Field
sage: phi.codomain().conductor()
530575705
sage: phi.codomain().conductor().factor()
5 * 11 * 1531 * 6301
}}}
Note that:
* the two curves are not isogenous, since their conductors are different
* the degree of the isogeny is reported to be 1, but it should be 5.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/6384>
Sage <http://sagemath.org/>
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