Large Families of Cospectral Graphs

Seidel switching is an operation on graphs G satisfyingcertain regularity properties so that the resulting graph Hhas the same spectrum as G. If G issimple then the complement of G and the complementof H are also cospectral. We use a generalizationof Seidel switching to construct exponentially large familiesof cospectral graphs with cospectral complements.