Are unbounded linear operators computable on the average for Gaussian measures?

Abstract

Traub and Werschulz [Complexity and Information, Cambridge University Press, New York, 1999] ask whether every linear operator S: ⊆ X → Y is "computable on the average" w.r.t. a Gaussian measure on X. The question is inspired by an analogous result in information-based complexity on the averagecase solvability of linear approximation problems. We give several interpretations of Traub and Werschulz' question within the framework of type-2 theory of effectivity. We have negative answers to all of these interpretations but the one with minimal requirements on the algorithm's uniformness. On our way to these results, we give an effective version of the Mourier-Prokhorov characterization of Gaussian measures on separable Hilbert spaces.