yuwenlidao / pythonhmm

A simple Python implementation of the Hidden Markov Model.

PythonHMM

PythonHMM is a python implementation of the Hidden Markov Model.

Usage

To use PythonHMM, you must import the hmm module.

import hmm

Then, you can create an instance of Model by passing the states, symbols, and (optional) probability matrices.

states = ('rainy', 'sunny')
symbols = ('walk', 'shop', 'clean')

start_prob = {
    'rainy' : 0.5,
    'sunny' : 0.5
}

trans_prob = {
    'rainy': { 'rainy' : 0.7, 'sunny' : 0.3 },
    'sunny': { 'rainy' : 0.4, 'sunny' : 0.6 }
}

emit_prob = {
    'rainy': { 'walk' : 0.1, 'shop' : 0.4, 'clean' : 0.5 },
    'sunny': { 'walk' : 0.6, 'shop' : 0.3, 'clean' : 0.1 }
}

model = hmm.Model(states, symbols, start_prob, trans_prob, emit_prob)

Now, you can evaluate and decode the given sequence:

sequence = ['walk', 'shop', 'clean', 'clean', 'walk', 'walk', 'walk', 'clean']

print model.evaluate(sequence)
print model.decode(sequence)

You can also using the given sequences (a list of (state list, symbol list) pair) to train a model:

sequences = [
    (state_list1, symbol_list1),
    (state_list2, symbol_list2),
    ...
    (state_listN, symbol_listN),
]

model = hmm.train(sequences)

The train function also has two optional arguments, delta and smoothing.

The delta argument (which is defaults to 0.0001) specifies that the learning algorithm will stop when the difference of the log-likelihood between two consecutive iterations is less than delta.

The smoothing argument (which is defaults to 0) is the smoothing parameter of the additive smoothing to avoid zero probability.

License

This project is BSD-licensed. See LICENSE file for more detail.