Hermitian-Randi\'c matrix and Hermitian-Randi\'c energy of mixed graphs
  Let $M$ be a mixed graph and $H(M)$ be its Hermitian-adjacency matrix. If we add every edge and arc in $M$ a Randi\'c weight, then we can get a new weighted Hermitian-adjacency matrix. What are the properties of this new matrix? Motivated by this, we define the Hermitian-Randi\'c matrix $R_{H}(M)=(r_{h})_{kl}$ of a mixed graph $M$, where $(r_{h})_{kl}=-(r_{h})_{lk}=\frac{\textbf{i}}{\sqrt{d_{k}d_{l}}}$ ($\textbf{i}=\sqrt{-1}$) if $(v_{k},v_{l})$ is an arc of $M$, $(r_{h})_{kl}=(r_{h})_{lk}=\frac{1}{\sqrt{d_{k}d_{l}}}$ if $v_{k}v_{l}$ is an undirected edge of $M$, and $(r_{h})_{kl}=0$ otherwise.   In this paper, firstly, we compute the characteristic polynomial of the Hermitian-Randi\'c matrix of a mixed graph. Furthermore, we give bounds to the Hermitian-Randi\'c energy of a general mixed graph. Finally, we give some results about the Hermitian-Randi\'c energy of mixed trees. 
Yong Lu, Ligong Wang, Qiannan Zhou
math.CO