Fast and Consistent Learning of Hidden Markov Models by Incorporating Non-Consecutive Correlations

CHAPTER A Hidden Markov Models Chapter 17 introduced the Hidden Markov Model and applied it to part of speech tagging. Part of speech tagging is a fully-supervised learning task, because we have a corpus of words labeled with the correct part-of-speech tag. But many applications don't have labeled data. So in this chapter, we introduce the full set of algorithms for HMMs, including the key unsupervised learning algorithm for HMM, the Forward-Backward algorithm. We'll repeat some of the text from Chapter 17 for readers who want the whole story laid out in a single chapter. A.1 Markov Chains The HMM is based on augmenting the Markov chain. A Markov chain is a model Markov chain