The Signed Positive Semidefinite Matrix Completion Problem for Odd-$K_4$ Minor Free Signed Graphs

TL;DR

This paper extends Laurent's theorem to signed graphs, characterizing positive semidefinite matrix completions for odd-$K_4$ minor free signed graphs and exploring their rigidity and rank properties.

Contribution

It provides a signed generalization of Laurent's theorem and characterizes maximum rank completions for odd-$K_4$ minor free signed graphs.

Findings

Characterization of feasible positive semidefinite matrix completions.

Boundaries on minimum rank for these completions.

Conditions for universal rigidity of spherical tensegrities.

Abstract

We give a signed generalization of Laurent's theorem that characterizes feasible positive semidefinite matrix completion problems in terms of metric polytopes. Based on this result, we give a characterization of the maximum rank completions of the signed positive semidefinite matrix completion problem for odd-$K_4$ minor free signed graphs. The analysis can also be used to bound the minimum rank over the completions and to characterize uniquely solvable completion problems for odd-$K_4$ minor free signed graphs. As a corollary we derive a characterization of the universal rigidity of odd-$K_4$ minor free spherical tensegrities, and also a characterization of signed graphs whose signed Colin de Verdi\`ere parameter $\nu$ is bounded by two, recently shown by Arav et al.