Baum's forward-backward algorithm revisited

  • Authors:
  • Pierre A Devijver

  • Affiliations:
  • Philips Research Laboratory, Avenue Van Becelaere 2, Box 8, B-1170 Brussels, Belgium

  • Venue:
  • Pattern Recognition Letters
  • Year:
  • 1985

Quantified Score

Hi-index 0.10

Visualization

Abstract

In this note, we examine the forward-backward algorithm from the computational viewpoint of the underflow problem inherent in Baum's (1972) original formulation. We demonstrate that the conversion of Baum's computation of joint likelihoods into the computation of posterior probabilities results in essentially the same algorithm, except for the presence of a scaling factor suggested by Levinson et al. (1983) on rather heuristic grounds. The resulting algorithm is immune to the underflow problem, and Levinson's scaling method is given a theoretical justification. We also investigate the relationship between Baum's algorithm and the recent algorithms of Askar and Derin (1981) and Devijver (1984).