Preface to the Special Issue of ILAS 2019: Linear Algebra without Borders, The 22ndILAS Conference, Rio de Janeiro, Brazil, July 08-12, 2019

Let G a graph on n vertices. The signless Laplacian matrix of G, denoted by Q(G), is defined as Q(G)=D(G)+A(G), where A(G) is the adjacency matrix of G and D(G) is the diagonal matrix of the degrees of G. A graph G is said to be Q-integral if all eigenvalues of the matrix Q(G) are integers. In this paper, we characterize all Q-integral graphs among all connected graphs with at most two vertices of degree greater than or equal to three.