  Electromagnetic circuits are the electromagnetic analog at fixed frequency of
mass-spring networks in elastodynamics. By interchanging the roles of epsilon
and mu in electromagnetic circuits one obtains magnetoelectric circuits. Here
we show that by introducing tetrahedral connectors having epsilon=mu=0 one can
join electromagnetic and magnetoelectric circuits to obtain hybrid circuits.
Their response is governed by a symmetric matrix with negative semidefinite
imaginary part. Conversely given any such matrix a recipe is given for
constructing a hybrid circuit which has that matrix as its response matrix.
