Adjoints and Canonical Forms of Polypols
Abstract
Polypols are natural generalizations of polytopes, with boundaries given by nonlinear algebraic hypersurfaces. We describe polypols in the plane and in 3-space that admit a unique adjoint hypersurface and study them from an algebro-geometric perspective. We relate planar polypols to positive geometries introduced originally in particle physics, and identify the adjoint curve of a planar polypol with the numerator of the canonical differential form associated with the positive geometry. We settle several cases of a conjecture by Wachspress claiming that the adjoint curve of a regular planar polypol does not intersect its interior. In particular, we provide a complete characterization of the real topology of the adjoint curve for arbitrary convex polygons. Finally, we determine all types of planar polypols such that the rational map sending a polypol to its adjoint is finite, and explore connections of our topic with algebraic statistics.
Keywords
Cite
@article{arxiv.2108.11747,
title = {Adjoints and Canonical Forms of Polypols},
author = {Kathlén Kohn and Ragni Piene and Kristian Ranestad and Felix Rydell and Boris Shapiro and Rainer Sinn and Miruna-Stefana Sorea and Simon Telen},
journal= {arXiv preprint arXiv:2108.11747},
year = {2025}
}