From HMMs to Probabilistic Regular Grammars (PRG)

• A PRG has start state N1 and rules of the form:

  • Ni --> wj Nk
  • Ni --> wj

• This is similar to what we had for an HMM except that in an HMM, we have ?n ?w1n P(w1n) = 1 whereas in a PCFG, we have ? w?L P(w) = 1 where L is the language generated by the grammar.

• PRG are related to HMMs in that a PRG is a HMM to which we should add a start state and a finish (or sink) state.

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