American Citizen on Mon, 15 Apr 2024 02:51:30 +0200


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general question relating to elliptic curves and their rational points and creating a pool of rational points of count N


Hello:

I am currently working with rational Diophantine sextuples, example: [5/4, 5/36, 32/9, 189/4, 665/1521, 3213/676] where the product of any pair + 1 is a rational square.

If we select 3 of the ratios, making a triple, say [5/4, 5/36, 32/9], we can create an elliptic curve associated with the triple [a,b,c]

E:  [0,(a*b+a*c+b*c),0,(a*b*c)*(a+b+c),(a*b*c)^2]

I have been working with 758 sextuples, and found elliptic curves of rank =1 through rank = 10 for Diophantine triples derived from the sextuples. (20 triples per sextuple).

My question to the group is this, given the Mordell-Weil basis (which seems quite easy to find for E), how can I determine a cut-off value of elliptic curve point heights for creating a pool of 10K points that are on the curve?

I am using a gp-pari command called "ellpool(E,p,h)" where E is the curve, p is the Mordell-Weil basis and h is the maximum height of the points stored in the pool (or lattice or vector) of rational points. By carefully adding points from the MW basis, we can slowly build a pool of points on the curve <= h.

I need to determine h such that the count of the pool is around 10K or so. Determining h seems somewhat hard to figure out, although I was using the regulator^(1/rank) * F to set the height h (where F is around 5 to 12 or so) and that generally works, but not always. Of  course the torsion group for the curve E plays a huge part too in finding the pool of points, as the torsion points automatically increase the rational points found.

Has someone done this work before? Can any papers be cited?

Right now I am setting this ad-hoc, but wish that a better scheme could be found.

Example:

% find([5/4, 5/36, 32/9])

rank = 2,

curve = [0, 6625/1296, 0, 2225/729, 2500/6561]

MW_basis = [[124/9, 4879/81], [1600/9, 194750/81]]

triple: [5/4, 5/36, 32/9]

And playing around with h in the ellpool(e,p,h) command eventually finds h = 942 gives 9979 points, 943 = 9987 points, and 944 = 10027 points so 943.5 gives 10003 points which is close enough.

The regulator of this curve is 12.62021889005498 and the rank = 2, so taking reg^(1/rank) gives F = 265.588 above in order to come out to 943.5

Any ideas on a better way to find h? The curve is a Z2xZ2 curve.

Randall