#6384: elliptic curve -- isogeny function is not robust -- it doesn't check
validity of its input
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Reporter: was | Owner: shumow
Type: defect | Status: new
Priority: major | Milestone: sage-4.1
Component: algebra | Keywords:
Reviewer: | Author:
Merged: |
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Comment(by wuthrich):
Moreover there is the following bug in the doctest:
{{{
sage: E = EllipticCurve(GF(31),[1,0,0,1,2])
sage: phi = E.isogeny([14,27,4,1])
sage: phi.degree()
7
sage: E.division_polynomial(7).factor()
(7) * (x^24 + 2*x^23 + ... + 15*x + 22)
}}}
in other words there can not be an isogeny of degree 7 defined over the
ground field. The given polynomial is a factor of the 3-division
polynomial. But it can not define an isogeny of degree 3 as the kernel
would have 6 elements.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/6384#comment:5>
Sage <http://sagemath.org/>
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