Comments on "Structural Invariant Subspaces of Singular Hamiltonian Systems and Nonrecursive Solutions of Finite-Horizon Optimal Control Problems"

In this note the paper "Structural Invariant Subspaces of Singular Hamiltonian Systems and Nonrecursive Solutions of Finite-Horizon Optimal Control Problems" is analyzed. It is shown that its main result concerning a characterization of a pair of structural invariant subspaces associated with the extended symplectic system, is a particular case of a result presented in other works within a more general and rigorous context. We also analyze the proof of the main result of the above mentioned paper, and the way such result is used to accommodate the boundary conditions in the solution of a finite-horizon linear quadratic optimal control problem.