#6113: segfault in division_points and factoring torsion_polynomial
---------------------------+------------------------------------------------
Reporter: ncalexan | Owner: was
Type: defect | Status: new
Priority: major | Milestone: sage-4.0.2
Component: number theory | Keywords: segfault division points torsion
polynomial
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John Cremona reports:
In 4.0.alpha0, this causes a segmentation fault:
{{{
----------------------------------------------------------------------
| Sage Version 4.0.alpha0, Release Date: 2009-05-15 |
| Type notebook() for the GUI, and license() for information. |
----------------------------------------------------------------------
sage: K.<a>=NumberField(x^2-x+22)
sage: w=-13*a-14
sage: E=EllipticCurve([0,0,0,0,-1728*w])
sage: P1 = E.lift_x(-3*a-66)
sage: P2 = E.lift_x((-21*a-93)/4)
sage: P2.division_points(19)
}}}
It works fine to do
{{{
sage: g = P2.division_points(19, poly_only=True)
}}}
which defines a polynomial of degree 361 over Q(sqrt(-87)), but then
g.roots() goes Boom.
ncalexan verified this on Mac OS X; it looks like the crash is in an NTL
function:
{{{
(gdb) bt
#0 0x01293247 in modii ()
#1 0x014278bc in FpX_red ()
}}}
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/6113>
Sage <http://sagemath.org/>
Sage - Open Source Mathematical Software: Building the Car Instead of
Reinventing the Wheel
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