Structured strong linearizations of structured rational matrices

Abstract: Structured rational matrices such as symmetric, skew-symmetric, Hamiltonian, skew-Hamiltonian, Hermitian, and para-Hermitian rational matrices arise in many applications. Linearizations of rational matrices have been introduced recently for computing poles, eigenvalues, eigenvectors, minimal bases and minimal indices of rational matrices. For structured rational matrices, it is desirable to construct structure-preserving linearizations so as to preserve the symmetry in the eigenvalues and poles of the rational matrices. With a view to constructing structure-preserving linearizations of structured rational matrices, we propose a family of Fiedler-like pencils and show that the family of Fiedler-like pencils is a rich source of structure-preserving strong linearizations of structured rational matrices. We construct symmetric, skew-symmetric, Hamiltonian, skew-Hamiltonian, Hermitian, skew-Hermitian, para-Hermitian and para-skew-Hermitian strong linearizations of a rational matrix $G(\lambda)$ when $G(\lambda)$ has the same structure. Further, when $G(\lambda)$ is real and symmetric, we show that the transfer functions of real symmetric linearizations of $G(\lambda)$ preserve the Cauchy-Maslov index of $G(\lambda).$ We describe the recovery of eigenvectors, minimal bases and minimal indices of $G(\lambda)$ from those of the linearizations of $G(\lambda)$ and show that the recovery is operation-free.