#5065: elliptic curve torsion subgroup doesn't know its identity
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Reporter: boothby | Owner: was
Type: defect | Status: new
Priority: minor | Milestone: sage-4.0
Component: number theory | Keywords:
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Comment(by cremona):
Here is the reason. the torsion subgroup class is derived from the
Abelian group class, which in Sage is always a multiplicative group! So
it can coerce in 1 to give the identity 1, but not 0.
I produced a lovely patch adding proper additive support to the
AbelianGroup class months ago, motivated mainly by situations such as
this, but nobody else was interested and it never got in. (To be fair,
the patch is on trac labelled "not for review" for some reason).
Of course, for this specific group we could easily write a call() function
to handle this, but the whole point of my Abeliangroup patch was that if
you say that a group is additive on creation then that was all automatic.
Sigh.
I see that this was reported 3 months ago. Sorry, I never saw it until
now!
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/5065#comment:3>
Sage <http://sagemath.org/>
Sage - Open Source Mathematical Software: Building the Car Instead of
Reinventing the Wheel
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