Learning probabilistic automata: A study in state distinguishability

  • Authors:
  • Borja Balle;Jorge Castro;Ricard Gavaldà

  • Affiliations:
  • -;-;-

  • Venue:
  • Theoretical Computer Science
  • Year:
  • 2013

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Abstract

Known algorithms for learning PDFA can only be shown to run in time polynomial in the so-called distinguishability @m of the target machine, besides the number of states and the usual accuracy and confidence parameters. We show that the dependence on @m is necessary in the worst case for every algorithm whose structure resembles existing ones. As a technical tool, a new variant of Statistical Queries termed L"~-queries is defined. We show how to simulate L"~-queries using classical Statistical Queries and show that known PAC algorithms for learning PDFA are in fact statistical query algorithms. Our results include a lower bound: every algorithm to learn PDFA with queries using a reasonable tolerance must make @W(1/@m^1^-^c) queries for every c0. Finally, an adaptive algorithm that PAC-learns w.r.t. another measure of complexity is described. This yields better efficiency in many cases, while retaining the same inevitable worst-case behavior. Our algorithm requires fewer input parameters than previously existing ones, and has a better sample bound.