The index of matrix A in Cn.n is equivalent to the dimension of largest Jor-dan block corresponding to the zero eigenvalue of A. In this paper, indicialequations and normal equations for solving inconsistent singular linear systemof equations are investigated.

Notation: λ1(A) = largest eigenvalue of A. Motivation: The largest eigenvalue tells us the spectrum of a matrix and thus can be somewhat useful. More crucially for the adjacency matrix of a graph, we know exactly that the all one’s vector is the largest eigenvector, and thus by working orthogonal to this vector we can approximate the second largest eigenvalue of the graph, which tells us how we...

We give an upper bound for the largest eigenvalue of a nonregular graph with n vertices and the largest vertex degree ∆.

Let L(G) be the Laplacian matrix of G. In this paper, we characterize all of the connected graphs with second largest Laplacian eigenvalue no more than l; where l . = 3.2470 is the largest root of the equation μ3 − 5μ2 + 6μ − 1 = 0. Moreover, this result is used to characterize all connected graphs with second largest Laplacian eigenvalue no more than three. © 2013 Elsevier Ltd. All rights rese...