Skew orthogonal polynomials arise in the calculation of the n-point distribution function for the eigenvalues of ensembles of random matrices with orthogonal or symplectic symmetry. In particular, the distribution functions are completely determined by a certain sum involving the skew orthogonal polynomials. In the cases that the eigenvalue probability density function involves a classical weig...

The eccentricity e(v) of a vertex v in a strongly connected digraph G is the maximum distance from v. The eccentricity sequence of a digraph is the list of eccentricities of its vertices given in nondecreasing order. A sequence of positive integers is a digraphical eccentric sequence if it is the eccentricity sequence of some digraph. A set of positive integers S is a digraphical eccentric set ...

The tree-shaped facility location problem aims to locate a subtree on the center of a given tree network. This paper deals with four types of the problems in which the centrality for a subtree is measured by the eccentricity or the distance-sum, and a subtree may contain partial edges or not. We investigate the relationship between these problems and knapsack-type problems. The relation leads t...

Let Γ be a regular graph with n vertices, diameter D, and d + 1 different eigenvalues λ > λ1 > · · · > λd. In a previous paper, the authors showed that if P (λ) > n − 1, then D ≤ d − 1, where P is the polynomial of degree d−1 which takes alternating values±1 atλ1, . . . , λd. The graphs satisfying P (λ) = n − 1, called boundary graphs, have shown to deserve some attention because of their rich ...

In this paper, a fundamentally new method, based on the denition, is introduced for numerical computation of eigenvalues, generalized eigenvalues and quadratic eigenvalues of matrices. Some examples are provided to show the accuracy and reliability of the proposed method. It is shown that the proposed method gives other sequences than that of existing methods but they still are convergent to th...

We highlight some properties of the field of values (or numerical range) W (P ) of an oblique projector P on a Hilbert space, i.e., of an operator satisfying P 2 = P . If P is neither null nor the identity, we present a direct proof showing that W (P ) = W (I − P ), i.e., the field of values of an oblique projection coincides with that of its complementary projection. We also show that W (P ) i...

• Let G be a graph. For subset X of V ( ), the switching σ is signed graph obtained from by reversing signs all edges between and ) ∖ . A( adjacency matrix An eigenvalue called main if it has an eigenvector sum whose entries not equal to zero. Two equivalent graphs share same spectrum, while they may have different eigenvalues. Akbari et al. (2021) conjectured that let ≠ K 2 , 4 { e } Then ther...

Let G be a simple connected graph. The transmission of any vertex v of a graph G is defined as the sum of distances of a vertex v from all other vertices in a graph G. Then the distance signless Laplacian matrix of G is defined as D^{Q}(G)=D(G)+Tr(G), where D(G) denotes the distance matrix of graphs and Tr(G) is the diagonal matrix of vertex transmissions of G. For a given minimum dominating se...

given a graph $g$, let $g^sigma$ be an oriented graph of $g$ with the orientation $sigma$ and skew-adjacency matrix $s(g^sigma)$. then the spectrum of $s(g^sigma)$ consisting of all the eigenvalues of $s(g^sigma)$ is called the skew-spectrum of $g^sigma$, denoted by $sp(g^sigma)$. the skew energy of the oriented graph $g^sigma$, denoted by $mathcal{e}_s(g^sigma)$, is defined as the sum of the n...