From External to Internal System Decompositions

The recently obtained approach to the construction of state maps, which is directly based on the linear differential operator describing the system, is shown to lead to an immediate and insightful relation between external and internal decompositions and symmetries of a linear system. This is applied to the decomposition of a system into its controllable and uncontrollable part (in the state space representation commonly referred to as the Kalman decomposition), and to the correspondence between external and internal symmetries.