Computability of the Radon-Nikodym derivative

  • Authors:
  • Mathieu Hoyrup;Cristóbal Rojas;Klaus Weihrauch

  • Affiliations:
  • LORIA, INRIA Nancy-Grand Est, Vandœuvre-lès-Nancy, France;Department of Mathematics, University of Toronto, Toronto, ON, Canada;Fakultät für Mathematik und Informatik, FernUniversität Hagen, Hagen, Germany

  • Venue:
  • CiE'11 Proceedings of the 7th conference on Models of computation in context: computability in Europe
  • Year:
  • 2011

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Abstract

We show that a single application of the noncomputable operator EC, which transforms enumerations of sets (in N) to their characteristic functions, suffices to compute the Radon-Nikodym derivative dµ/dλ of a finite measure µ, which is absolutely continuous w.r.t. the σ-finite measure λ. We also give a condition on the two measures (in terms of computability of the norm of a certain linear operator involving the two measures) which is sufficient to compute the derivative.