The Baum–Welch algorithm is a particular case of a generalized expectation-maximization (GEM) algorithm.
It can compute maximum likelihood estimates and posterior mode estimates for the parameters (transition
and emission probabilities) of an HMM, when given only emissions as training data.
http://en.wikipedia.org/wiki/Baum%E2%80%93Welch_algorithm
The Baum–Welch algorithm is a particular case of a generalized expectation-maximization (GEM) algorithm. It can compute maximum likelihood estimates and posterior mode estimates for the parameters (transition and emission probabilities) of an HMM, when given only emissions as training data.