A necessary condition for generic rigidity of bar-and-joint frameworks in $d$-space

Abstract

A graph $G=(V,E)$ is $d$-sparse if each subset $X\subseteq V$ with $|X|\geq d$ induces at most $d|X|-{{d+1}\choose{2}}$ edges in $G$. Maxwell showed in 1864 that a necessary condition for a generic bar-and-joint framework with at least $d+1$ vertices to be rigid in ${\mathbb R}^d$ is that $G$ should have a $d$-sparse subgraph with $d|X|-{{d+1}\choose{2}}$ edges. This necessary condition is also sufficient when $d=1,2$ but not when $d\geq 3$. Cheng and Sitharam strengthened Maxwell's condition by showing that every maximal $d$-sparse subgraph of $G$ should have $d|X|-{{d+1}\choose{2}}$ edges when $d=3$. We extend their result to all $d\leq 11$.Comment: There was an error in the proof of Theorem 3.3(b) in version 1 of this paper. A weaker statement was proved in version 2 and then used to derive the main result Theorem 4.1 when $d\leq 5$. The proof technique was subsequently refined in collaboration with Hakan Guler to extend this result to all $d\leq 11$ in Theorem 3.3 of version