Convergence theorems for barycentric maps

Abstract

We first develop a theory of conditional expectations for random variables with values in a complete metric space $M$ equipped with a contractive barycentric map $\beta$, and then give convergence theorems for martingales of $\beta$-conditional expectations. We give the Birkhoff ergodic theorem for $\beta$-values of ergodic empirical measures and provide a description of the ergodic limit function in terms of the $\beta$-conditional expectation. Moreover, we prove the continuity property of the ergodic limit function by finding a complete metric between contractive barycentric maps on the Wasserstein space of Borel probability measures on $M$. Finally, the large derivation property of $\beta$-values of i.i.d. empirical measures is obtained by applying the Sanov large deviation principle.