A Cosine Rule-Based Discrete Sectional Curvature for Graphs

TL;DR

This paper introduces a new estimator for discrete sectional curvature in graphs, validated on geometric graphs with low metric distortion, with applications in geospatial and fractal analysis.

Contribution

It proposes a cosine rule-based curvature estimator for graphs constructed on manifolds, validated through numerical experiments and practical applications.

Findings

Curvature estimate error decreases with lower metric distortion.

Estimator converges to true curvature as distortion approaches zero.

Outperforms existing discrete curvature measures in validation tests.

Abstract

How does one generalize differential geometric constructs such as curvature of a manifold to the discrete world of graphs and other combinatorial structures? This problem carries significant importance for analyzing models of discrete spacetime in quantum gravity; inferring network geometry in network science; and manifold learning in data science. The key contribution of this paper is to introduce and validate a new estimator of discrete sectional curvature for random graphs with low metric-distortion. The latter are constructed via a specific graph sprinkling method on different manifolds with constant sectional curvature. We define a notion of metric distortion, which quantifies how well the graph metric approximates the metric of the underlying manifold. We show how graph sprinkling algorithms can be refined to produce hard annulus random geometric graphs with minimal metric distortion. We construct random geometric graphs for spheres, hyperbolic and euclidean planes; upon which we validate our curvature estimator. Numerical analysis reveals that the error of the estimated curvature diminishes as the mean metric distortion goes to zero, thus demonstrating convergence of the estimate. We also perform comparisons to other existing discrete curvature measures. Finally, we demonstrate two practical applications: (i) estimation of the earth's radius using geographical data; and (ii) sectional curvature distributions of self-similar fractals.