Curve equations from expansions of 1-forms at a nonrational point

Raymond van Bommel, Edgar Costa, Bjorn Poonen, Padmavathi Srinivasan

Research output: Chapter in Book/Report/Conference proceedingChapter in a book

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 $\mathbb{Q}$ for many hyperelliptic modular curves without a rational cusp in the L-functions and Modular Forms Database.
Original languageEnglish
Title of host publicationContemporary Mathematics
PublisherAmerican Mathematical Society
Number of pages9
DOIs
Publication statusAccepted/In press - 6 Aug 2025

Publication series

NameContemporary Mathematics
PublisherAmerican Mathematical Society
ISSN (Print)0271-4132

Bibliographical note

10 pages, comments welcome

Keywords

  • math.NT
  • 14Q05 (Primary) 11G18, 14G35 (Secondary)

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