Book Image

Hands-On Markov Models with Python

By : Ankur Ankan, Abinash Panda
Book Image

Hands-On Markov Models with Python

By: Ankur Ankan, Abinash Panda

Overview of this book

Hidden Markov Model (HMM) is a statistical model based on the Markov chain concept. Hands-On Markov Models with Python helps you get to grips with HMMs and different inference algorithms by working on real-world problems. The hands-on examples explored in the book help you simplify the process flow in machine learning by using Markov model concepts, thereby making it accessible to everyone. Once you’ve covered the basic concepts of Markov chains, you’ll get insights into Markov processes, models, and types with the help of practical examples. After grasping these fundamentals, you’ll move on to learning about the different algorithms used in inferences and applying them in state and parameter inference. In addition to this, you’ll explore the Bayesian approach of inference and learn how to apply it in HMMs. In further chapters, you’ll discover how to use HMMs in time series analysis and natural language processing (NLP) using Python. You’ll also learn to apply HMM to image processing using 2D-HMM to segment images. Finally, you’ll understand how to apply HMM for reinforcement learning (RL) with the help of Q-Learning, and use this technique for single-stock and multi-stock algorithmic trading. By the end of this book, you will have grasped how to build your own Markov and hidden Markov models on complex datasets in order to apply them to projects.
Table of Contents (11 chapters)

The Viterbi algorithm

So far, we have been trying to compute the different conditional and joint probabilities in our model. But one thing that we can't do with the forward-backward algorithm is find the most probable state of the hidden variables in the model given the observations. Formally, we can write this problem as, we know the observed variable, the transition probabilities and the emission probability of the network and we would like to compute Z*, which is defined as:


Z={Z1, Z2, …, Zn}


X={X1, X2, …, Xn}

Properties of operations on probability distributions:
When we do operations on the probability distributions (marginalization, maximization, and so on), we can push in the operation through the independent terms of the distribution. We can see these examples in the case of marginalization and argmax:

Figure 3.6: HMM showing three...