New bounds of extended energy of a graph

arXiv2212.02767MaRDI QIDQ6419666

Abujafar Mandal, Sk. Md. Abu. Nayeem

Publication date: 6 December 2022

Abstract: Extended adjacency matrix of a graph with $n$ vertices is a real symmetric marix of order $nimesn$ whose $(i,j)$-th entry is the average of the ratio of the degree of the vertex $i$ to that of the vertex $j$ and its reciprocal when $i,j$ are adjacent, and zero otherwise. Aggregate of absolute eigenvalues of the extended adjacency matrix is termed as the extended energy. In this paper, the concept of extended vertex energy is introduced and some bounds of extended vertex energy are obtained. From there, we obtain some new upper bounds of the extended energy of a graph. Next, we obtain two inequalities which relate the extended energy with the ordinary graph energy. One of those inequalities resolves a conjecture which states that for every graph, ordinary energy can never exceed the extended energy. Using the relationships of extended energy and ordinary energy, we obtain new bounds of extended energy involving the order, size, largest and smallest degree of the graph. We show that these new bounds are improvements of some existing bounds. Finally, some improved bounds of Nordhaus-Gaddum-type are also found.

Mathematics Subject Classification ID

Graphs and linear algebra (matrices, eigenvalues, etc.) (05C50) Vertex degrees (05C07)

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