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arXiv · 2601.15421

Counting point configurations in projective space

Alex Fink·Navid Nabijou·Rob Silversmith
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Abstract

We investigate the enumerative geometry of point configurations in projective space. We define "projective configuration counts": these enumerate configurations of points in projective space such that certain specified subsets are in fixed relative positions. The $\mathbb{P}^1$ case recovers cross-ratio degrees, which arise naturally in numerous contexts. We establish two main results. The first is a combinatorial upper bound given by the number of weighted transversals of a bipartite graph. The second is a recursion that relates counts associated to projective spaces of different dimensions, by projecting away from a given point. Key inputs include the Gelfand-MacPherson correspondence, the Jacobi-Trudi and Thom-Porteous formulae, and the notion of surplus from matching theory of bipartite graphs.

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Alex Fink, Navid Nabijou, Rob Silversmith. 2026-01-21. Counting point configurations in projective space. https://arxiv.org/abs/2601.15421

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