On Structural Non-commutativity in Affine Feedback of SISO Nonlinear Systems

Abstract

The affine feedback connection of SISO nonlinear systems modeled by Chen--Fliess series is shown to be a group action on the plant which is isomorphic to the semi-direct product of shuffle and additive group of non-commutative formal power series. The additive and multiplicative feedback loops in an affine feedback connection are thus proven to be structurally non-commutative. A flip in the order of these loops results in a net additive feedback loop.

submitted to $26^{th}$ International Symposium on Mathematical Theory of Networks and Systems, 2024