2024/01/31 by Sándor Bozóki, Bozóki, Sándor, G. Domokos +5
Computer Science · Engineering · #Advanced Graph Theory Research #Computational Geometry and Mesh Generation #graph theory and CDMA systems
paper · pdf · doi:10.48550/arxiv.2401.17906
We prove that every homogeneous convex polyhedron with only one unstable equilibrium (known as a mono-unstable convex polyhedron) has at least 7 vertices. Although it has been long known that no mono-unstable tetrahedra exist, and mono-unstable polyhedra with as few as 18 vertices and faces have been constructed, this is the first nontrivial lower bound on the number of vertices for a mono-unstable polyhedron. There are two main ingredients in the proof. We first establish two types of relationships, both expressible as (non-convex) quadratic inequalities, that the coordinates of the vertices of a mono-unstable convex polyhedron must satisfy, taking into account the combinatorial structure of the polyhedron. Then we use numerical semidefinite optimization algorithms to compute easily and independently verifiable, rigorous certificates that the resulting systems of quadratic inequalities (5943 in total) are indeed inconsistent in each case.