HMMs - Summary


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  • Decoding : what sequence of hidden (underlying) states most probably generated a given sequence of observations. The Viterbi algorithm solves this problem efficiently.

  • Learning : what model most probably underlies a given sample of observation sequences - that is, what are the parameters of such a model. This problem may be solved by using the forward-backward algorithm.
HMMs have proved to be of great value in analysing real systems; their usual drawback is the over-simplification associated with the Markov assumption - that a state is dependent only on predecessors, and that this dependence is time independent.

A full exposition on HMMs may be found in:

L R Rabiner and B H Juang, `An introduction to HMMs', iEEE ASSP Magazine, 3, 4-16.