On the Cycle Space of a Random Graph

Abstract: Write $\mathcal{C}(G)$ for the cycle space of a graph $G$, $\mathcal{C}\kappa(G)$ for the subspace of $\mathcal{C}(G)$ spanned by the copies of the $\kappa$-cycle $C\kappa$ in $G$, $\mathcal{T}\kappa$ for the class of graphs satisfying $\mathcal{C}\kappa(G)=\mathcal{C}(G)$, and $\mathcal{Q}\kappa$ for the class of graphs each of whose edges lies in a $C\kappa$. We prove that for every odd $\kappa \geq 3$ and $G=G_{n,p}$, [\max_p \, \Pr(G \in \mathcal{Q}\kappa \setminus \mathcal{T}\kappa) \rightarrow 0;] so the $C_\kappa$'s of a random graph span its cycle space as soon as they cover its edges. For $\kappa=3$ this was shown by DeMarco, Hamm and Kahn (2013).