Nakiboglu B.HAO-CHUNG CHENG2022-04-252022-04-252021https://www.scopus.com/inward/record.uri?eid=2-s2.0-85123404642&doi=10.1109%2fITW48936.2021.9611513&partnerID=40&md5=7d22c7ed3b7144d524c09cfe98b02e5bhttps://scholars.lib.ntu.edu.tw/handle/123456789/606950The existence of a unique Augustin mean and its invariance under the Augustin operator are established for arbitrary input distributions with finite Augustin information for channels with countably generated output σ-algebras. The existence is established by representing the conditional R?nyi divergence as a lower semi-continuous and convex functional in an appropriately chosen uniformly convex space and then invoking the Banach-Saks property in conjunction with the lower semi-continuity and the convexity. A new family of operators is proposed to establish the invariance of the Augustin mean under the Augustin operator for orders greater than one. Some members of this new family strictly decrease the conditional R?nyi divergence, when applied to the second argument of the divergence, unless the second argument is a fixed point of the Augustin operator. ? 2021 IEEE.Arbitrary inputsConvex spacesFixed pointsInput distributionsLower semicontinuityPropertySemi-continuousUniformly convexesInformation theory[SDGs]SDG10conference paper10.1109/ITW48936.2021.96115132-s2.0-85123404642