Transversal Passivity: Dissipation Relative to Input and Output Manifolds
This paper introduces transversal passivity, a local dissipation property for regulating input and output signals to prescribed manifolds. Its supply rate is built from the transverse port errors induced by nearest-point projections, so that motion along the manifolds is not penalized. We give a necessary condition and a constructive sufficient condition for the property and relate it to existing passivity notions. For feedback interconnections through negative-adjoint linear channels, power conservation no longer cancels the transverse supply. The residual is governed by compatibility defects that depend only on the channels and the prescribed manifolds, so it can be assessed before any closed-loop analysis, and it falls into a hierarchy of exact compatibility, quadratic cancellation, and nonzero quadratic residuals. Since transversal storages are only positive semidefinite, port convergence is obtained by combining compact confinement, for instance by conserved quantities, with a dissipation margin, and we identify a geometric obstruction under which no quadratic margin is available near the feasible states. A federated learning case study with heterogeneous data shows that port convergence can be certified even though no server target is compatible with the interconnection, and that the obstruction arises for a natural choice of target.