Coarse-Graining and Long-Range Response in Generated Systems

Abstract

Coarse-graining should retain the response to the perturbations and observations of interest. We study this requirement for systems defined by generating operations and observation maps. Equality of all allowed future outputs defines an observation-sufficient quotient; fibre consistency gives differentiable descent for bounded surjective linear maps between Banach spaces. Linearising the state equation and the observation together produces a response whose kernel, source, readout and direct term transform consistently under coarse-graining. We derive an exact comparison identity valid also for noninvertible coarse maps. Eliminating residual states yields a memory representation and, under decay bounds, controlled finite-memory approximations. For isolated critical modes, analytic Fredholm theory gives the pole and visibility conditions; reciprocal realisations with a positive crossing matrix have positive finite-rank residues. An arithmetic merge and a reflecting heat protocol illustrate these results by explicit calculations. Gaussian averaging and quantum-field-theory channels provide further realisations, including the identification of response poles with vacuum spectral atoms under matched spectral hypotheses.