Curve equations from expansions of 1-forms at a nonrational point
Abstract
We exhibit an algorithm to compute equations of an algebraic curve over a computable characteristic 0 field from the power series expansions of its regular 1-forms at a nonrational point of the curve, extending a 2005 algorithm of Baker, Gonz\'alez-Jim\'enez, Gonz\'alez, and Poonen for expansions at a rational point. If the curve is hyperelliptic, the equations present it as an explicit double cover of a smooth plane conic, or as a double cover of the projective line when possible. If the curve is nonhyperelliptic, the equations cut out the canonical model. The algorithm has been used to compute equations over for many hyperelliptic modular curves without a rational cusp in the L-functions and Modular Forms Database.
Cite
@article{arxiv.2506.14026,
title = {Curve equations from expansions of 1-forms at a nonrational point},
author = {Raymond van Bommel and Edgar Costa and Bjorn Poonen and Padmavathi Srinivasan},
journal= {arXiv preprint arXiv:2506.14026},
year = {2025}
}
Comments
10 pages, comments welcome