Willem H. Haemers

collaborators

4 papers

math.CO2014

Cospectral regular graphs with and without a perfect matching

Zoltan L. Blazsik, Jay Cummings, Willem H. Haemers

For each $b \geq 5$ we construct a pair of cospectral $b$ -regular graphs, where one has a perfect matching and the other one not. This solves a research problem posed by the third…

math.CO2014

Notes on simplicial rook graphs

Andries E. Brouwer, Sebastian M. Cioabă, Willem H. Haemers +1

The simplicial rook graph $SR (m, n)$ is the graph of which the vertices are the sequences of nonnegative integers of length $m$ summing to $n$ , where two such sequences are ad…

math.CO2014

Godsil-McKay switching and isomorphism

Aida Abiad, Andries E. Brouwer, Willem H. Haemers

Godsil-McKay switching is an operation on graphs that doesn't change the spectrum of the adjacency matrix. Usually (but not always) the obtained graph is non-isomorphic with the or…

math.CO2012

An odd characterization of the generalized odd graphs

Edwin R. van Dam, Willem H. Haemers

We show that any connected regular graph with $d + 1$ distinct eigenvalues and odd-girth $2 d + 1$ is distance-regular, and in particular that it is a generalized odd graph.