The row left rank of a quaternion unit gain graph in terms of maximum degree

Abstract: Let $\Phi=(G,U(\mathbb{Q}),\varphi)$ be a quaternion unit gain graph (or $U(\mathbb{Q})$-gain graph) of order $n$, $A(\Phi)$ be the adjacency matrix of $\Phi$ and $r(\Phi)$ be the row left rank of $\Phi$. Let $\Delta$ be the maximum degree of $\Phi$. In this paper, we prove that $r(\Phi)\geq\frac{n}{\Delta}$. Moreover, if $\Phi$ is connected, we obtain that $r(\Phi)\geq\frac{n-2}{\Delta-1}$. All the corresponding extremal graphs are characterized.