Optimal Synthesis in a Radially Symmetric Grushin Space

TL;DR

This paper analyzes the geometry and optimal control synthesis in a radially symmetric Grushin space, providing conditions for singularity structure and explicit descriptions of cut loci, especially in the integrable case.

Contribution

It offers a detailed analysis of optimal synthesis in a class of Carnot-Carathéodory spaces with radial symmetry, including explicit solutions in the integrable case.

Findings

Full description of the optimal synthesis at singular points.

Conditions ensuring a Grushin-like structure based on the function f(r).

Explicit characterization of the cut locus when f(r)=r.

Abstract

We study the geometry of $\mathbb{R}^3$ equipped with a rotationally invariant Carnot-Carth\'{e}odory metric obtained by weighting motion in the $z$-direction by a function $f(r)$ of the cylindrical radius. When $f$ vanishes only at $r=0$, the space exhibits a Grushin--type singularity along the vertical axis. We provide sufficient conditions on $f$ ensuring a Grushin--like structure and describe the full optimal synthesis at singular points. For Riemannian points, we propose a candidate cut time determined by a discrete symmetry of the Hamiltonian flow. In the integrable case $f(r)=r$, we prove that this candidate coincides with the true cut time and give an explicit description of the cut locus.