Generalizing the Markov and covariance interpolation problem using input-to-state filters

In the Markov and covariance interpolation problem a transfer function $W$ is sought that match the first coefficients in the expansion of $W$ around zero and the first coefficients of the Laurent expansion of the corresponding spectral density $W{W}^{\star }$. Here we solve an interpolation problem where the matched parameters are the coefficients of expansions of $W$ and $W{W}^{\star }$ around various points in the disc. The solution is derived using input-to-state filters and is determined by simple calculations such as solving Lyapunov equations and generalized eigenvalue problems.