Annealing techniques for unsupervised statistical language learning

  • Authors:
  • Noah A. Smith;Jason Eisner

  • Affiliations:
  • Johns Hopkins University, Baltimore, MD;Johns Hopkins University, Baltimore, MD

  • Venue:
  • ACL '04 Proceedings of the 42nd Annual Meeting on Association for Computational Linguistics
  • Year:
  • 2004

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Abstract

Exploiting unannotated natural language data is hard largely because unsupervised parameter estimation is hard. We describe deterministic annealing (Rose et al., 1990) as an appealing alternative to the Expectation-Maximization algorithm (Dempster et al., 1977). Seeking to avoid search error, DA begins by globally maximizing an easy concave function and maintains a local maximum as it gradually morphs the function into the desired non-concave likelihood function. Applying DA to parsing and tagging models is shown to be straightforward; significant improvements over EM are shown on a part-of-speech tagging task. We describe a variant, skewed DA, which can incorporate a good initializer when it is available, and show significant improvements over EM on a grammar induction task.