There is also this old trac ticket
<https://github.com/sagemath/sage/issues/23154> about implementing fast
arithmetic in genus 2 Jacobians, which never made it into Sage.  I've CCed
Mike Jabobson, who worked on it.
David


On Tue, Mar 12, 2024 at 12:10 PM Giacomo Pope <giacomop...@gmail.com> wrote:

> Thank you for linking this and I agree this is a great way to
> cross-compare the work we have been doing. I am not an expert in this area
> so I am not sure I should do a full review but I'm happy to look over it if
> this helps.
>
> As a small update on this work, I now have
>
> class HyperellipticCurveSmoothModel(AlgebraicScheme_subscheme_toric)
>
> So this new class builds on top of AlgebraicScheme_subscheme_toric and the
> smooth projective model is built using a toric variety. The points on the
> curve are currently SchemeMorphism_point_toric_field, potentially I will
> need to make a child class of these if methods on the points themselves are
> required.
>
> With the working arithmetic and this new inheritance my work is now going
> to be the rather slow and painful rewrite of all hyperelliptic methods from
> the current implementation to ensure everything works on the smooth degree
> model.
>
> On Monday, March 11, 2024 at 6:23:38 AM UTC Kwankyu Lee wrote:
>
>> On Friday, March 8, 2024 at 7:37:04 PM UTC+9 Giacomo Pope wrote:
>>
>> As a small update, the repository now contains code to
>>
>> - perform arithmetic for
>>   - the imaginary model (ramified, one point at infinity) for all cases
>>   - the real model (split, two points at infinity) for all cases
>>   - the real model (inert, zero points at infinity) for even genus
>>   Which allows us to do "as much" as Magma does for Jacobians of
>> hyperellipticc curves from the perspective of arithmetic.
>>
>> My current "test" for the arithmetic is that D - D = 0 for all cases,
>> that jacobian_order * D = zero and that order_from_multiple(D) works. If
>> people have other ideas for tests, please let me know. Of course at the
>> moment these tests are over finite fields but you can reasonable use other
>> fields (as Sabrina's message shows) but I am less sure about how to do
>> randomised testing here.
>>
>>
>> I just set https://github.com/sagemath/sage/pull/35467 to "needs review"
>> status. The PR implements Jacobian arithmetic for general projective curves.
>>
>> It is slow compared with Jacobian arithmetic using Mumford
>> representation, but could be used to crosscheck the computations.
>>
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