Maximal Energy Graphs

Unicyclic graphs with maximal energy

Let G be a graph on n vertices and let λ1, λ2, . . . , λn be its eigenvalues. The energy of G is defined as E(G) = |λ1| + |λ2| + · · · + |λn|. For various classes of unicyclic graphs, the graphs with maximal energy are determined. Let P 6 n be obtained by connecting a vertex of the circuit C6 with a terminal vertex of the path Pn−6. For n 7, P 6 n has the maximal energy among all connected unic...

Graphs and matrices with maximal energy

Given a complex m n matrix A; we index its singular values as 1 (A) 2 (A) ::: and call the value E (A) = 1 (A)+ 2 (A)+ ::: the energy of A; thereby extending the concept of graph energy, introduced by Gutman. Koolen and Moulton proved that E (G) (n=2) (1 + p n) for any graph G of order n and exhibited an in…nite family of graphs with E (G) = (v (G) =2) 1 + p v (G) . We prove that for all su¢ ci...

Threshold graphs of maximal Laplacian energy

The Laplacian energy of a graph sums up the absolute values of the differences of average degree and eigenvalues of the Laplace matrix of the graph. This spectral graph parameter is upper bounded by the energy obtained when replacing the eigenvalues with the conjugate degree sequence of the graph, in which the i-th number counts the nodes having degree at least i. Because the sequences of eigen...

Regular graphs with maximal energy per vertex

Line graphs associated to the maximal graph

Let $R$ be a commutative ring with identity. Let $G(R)$ denote the maximal graph associated to $R$, i.e., $G(R)$ is a graph with vertices as the elements of $R$, where two distinct vertices $a$ and $b$ are adjacent if and only if there is a maximal ideal of $R$ containing both. Let $Gamma(R)$ denote the restriction of $G(R)$ to non-unit elements of $R$. In this paper we study the various graphi...