English

The $d$-dimensional realisation number of a rigid graph

Combinatorics 2026-02-25 v1 Algebraic Geometry Metric Geometry

Abstract

Determining the number of (complex) realisations of a rigid graph for a specific choice of edge lengths is a fundamental problem in discrete geometry. In this article we provide two new tools for determining realisation numbers in arbitrary dimensions: (i) we prove that subgraph inclusion translates to realisation number divisibility; and (ii) we provide lower bounds on realisation numbers under specific graph operations in all dimensions. We use these methods to prove that every triangulated sphere with nn vertices has at least 2n42^{n-4} edge-length equivalent realisations in 3-dimensions, extending a 2-dimensional result of Jackson and Owen in the case of planar graphs. Additionally, our tools solve a family of conjectures set by Grasegger regarding how 1-extensions, X-replacements, and V-replacements affect realisation numbers.

Keywords

Cite

@article{arxiv.2602.20766,
  title  = {The $d$-dimensional realisation number of a rigid graph},
  author = {Sean Dewar and Anthony Nixon and Ben Smith},
  journal= {arXiv preprint arXiv:2602.20766},
  year   = {2026}
}

Comments

26 pages, 7 figures

R2 v1 2026-07-01T10:49:41.922Z