State-Space Formulas for the Nehari-Takagi Problem for Nonexponentially Stable Infinite-Dimensional Systems

We obtain state-space formulas for the solution of the Nehari-Takagi/suboptimal Hankel norm approximation problem for infinite-dimensional systems with a nonexponentially stable generator, via the method of J-spectral factorization. We make key use of a purely frequency-domain solution of the problem.