A family of n n symmetric circulant (0, 1) matrices is studied. It is shown that the determinant
of each matrix is .−1/n−1.n − 1/, a property shared with the adjacency matrix of
the complete graph on n nodes. As a result, each matrix in this family generates an incomplete
graph that forms a counterexample to a recent conjecture. © 2000 Elsevier Science Inc. All
rights reserved.