#6384: [with patch, needs work] 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-4.1.1
Component: number theory | Keywords: elliptic curves, isogeny,
Reviewer: | Author:
Merged: |
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Changes (by wuthrich):
* cc: kohel (added)
Comment:
Hi.
I agree that we may want to discuss this further ... and maybe eventually
ask sage-nt for a vote on what should be done.
1) Currently the parameter 'algorithm' is of no use at all. As you can not
force the algorithm to be 'kohel' when a list of point is given. So this
option - in the current version - is totally obsolete and I am against
carrying it around for nothing. If someone really wants to force things,
he can always import the function and work directly with them. A user who
wants to create an isogeny will never want to choose this. If ever you
implement further algorithms, we can add it again without problem.
I agree that this "breaks" backward compatibility. But it is really
nowhere used in sage and I do not think that any user apart from the two
of us even noticed that it existed. I personally consider it a design
error and not an option that we must keep compatible with. But other
people may think differently about this.
2) The same goes for the compatibility issue here. We should not carry a
wrong initial design with us for the rest of all times, if no one has ever
used it.
On the other hand I agree with your speed arguement. I may be wrong, but I
think no one will ever want to use this function with n as large as it
would matter. In characteristic 0, the typical degree is hardly ever
bigger than 10. Over finite fields, I would think that the usual way of
using this function for large n would be through 'kohel', but I might be
wrong. Anyway, I think that we should not worry about the eventual slow
down. In most cases the subgroup is not computed previously to the use of
this function.
For both 1) and 2), I asked William Stein and David Kohel whether they
would agree with changing this in Barcelona.
Chris.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/6384#comment:9>
Sage <http://sagemath.org/>
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