1 citations · 1 across the 4 of their papers we have counts for
12 papers
On signed graphs with at most two eigenvalues unequal to
Willem H. Haemers, Hatice Topcu
We present the first steps towards the determination of the signed graphs for which the adjacency matrix has all but at most two eigenvalues equal to 1 or -1. Here we deal with the…
Graph toughness from Laplacian eigenvalues
Xiaofeng Gu, Willem H. Haemers
The toughness of a graph is defined as , in which the minimum is taken over all such that is disconnected, wher…
Hoffman's ratio bound
Willem H. Haemers
Hoffman's ratio bound is an upper bound for the independence number of a regular graph in terms of the eigenvalues of the adjacency matrix. The bound has proved to be very useful a…
Universal spectra of the disjoint union of regular graphs
Willem H. Haemers, Mohammad Reza Oboudi
A universal adjacency matrix of a graph with adjacency matrix is any matrix of the form with , where is the identity matrix, is the…
Spectral symmetry in conference matrices
Willem H. Haemers, Leila Parsaei Majd
A conference matrix of order is an matrix with diagonal entries and off-diagonal entries satisfying . If is symmetric, then …
On sign-symmetric signed graphs
Ebrahim Ghorbani, Willem H. Haemers, Hamid Reza Maimani +1
A signed graph is said to be sign-symmetric if it is switching isomorphic to its negation. Bipartite signed graphs are trivially sign-symmetric. We give new constructions of non-bi…