A Geodesic Stratification of Two-dimensional Semi-algebraic Sets

TL;DR

This paper constructs a semi-algebraic stratification of planar semi-algebraic sets ensuring finite intersections with shortest paths, offering new insights into the structure of geodesics in semi-algebraic geometry.

Contribution

It introduces a specific stratification of planar semi-algebraic sets that guarantees finitely many geodesic segments within each cell, advancing understanding of geodesic behavior in semi-algebraic sets.

Findings

Provides a cell decomposition with finiteness property for geodesic intersections

Offers a framework for high-dimensional stratifications related to geodesics

Enhances understanding of shortest paths in semi-algebraic geometry

Abstract

Given any arbitrary semi-algebraic set $X$, any two points in $X$ may be joined by a piecewise $C^2$ path $\gamma$ of shortest length. Suppose $\mathcal{A}$ is a semi-algebraic stratification of $X$ such that each component of $\gamma \cap \mathcal{A}$ is either a singleton or a real analytic geodesic segment in $\mathcal{A}$, the question is whether $\gamma \cap \mathcal{A}$ has at most finitely many such components. This paper gives a semi-algebraic stratification, in particular a cell decomposition, of a real semi-algebraic set in the plane whose open cells have this finiteness property. This provides insights for high dimensional stratifications of semi-algebraic sets in connection with geodesics.