A method and apparatus are provided that reduce the amount of memory needed to perform forward-backward recursion to identify posterior probabilities. Under the invention, a forward recursion is performed to identify forward recursion scores. The forward recursion scores are then used directly in a backward recursion to determine posterior probabilities for each state in a set of time frames. The usefulness of this invention is especially high when there is a large number of discrete states, such as when there are more than one set of discrete states in the model.
