Hidden Markov Models

Definition
Usages
Summary

Section 2 - Page 4
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3. Learning

Generating a HMM from a sequence of obersvations
The third, and much the hardest, problem associated with HMMs is to take a sequence of observations (from a known set), known to represent a set of hidden states, and fit the most probable HMM; that is, determine the (P,A,B) triple that most probably describes what is seen.

The forward-backward algorithm is of use when the matrices A and B are not directly (empirically) measurable, as is very often the case in real applications.