On bipartite graphs having minimal fourth adjacency coefficient

Shi Cai Gong, Shao Wei Sun

Let $G$ be a simple graph with order $n$ and adjacency matrix $\mathbf{A}(G)$. Let $\varphi (G;\lambda )=\det (\lambda I-\mathbf{A}(G))={\sum }_{i=0}^n{\mathbf{a}}_i(G){\lambda }^{n-i}$ be the characteristic polynom…