Abstract:
Explicit formulas for calculating eigenvalues of the Hankel circulants, Hankel skew-circulants, $(T+H)$-circulants, and $(T+H)$-skew-circulants are obtained. It is shown that if $\phi\ne\pm1$, then the set of matrices that can be represented as sums of a Toeplitz $\phi$-circulant and a Hankel $\phi$-circulant is not an algebra.