  We study some (Hopf) algebraic properties of circulant matrices, inspired by
the fact that the algebra of circulant $n\times n$ matrices is isomorphic to
the group algebra of the cyclic group with $n$ elements. We introduce also a
class of matrices that generalize both circulant and skew circulant matrices,
and for which the eigenvalues and eigenvectors can be read directly from their
entries.
