Book Image

Machine Learning Algorithms - Second Edition

Book Image

Machine Learning Algorithms - Second Edition

Overview of this book

Machine learning has gained tremendous popularity for its powerful and fast predictions with large datasets. However, the true forces behind its powerful output are the complex algorithms involving substantial statistical analysis that churn large datasets and generate substantial insight. This second edition of Machine Learning Algorithms walks you through prominent development outcomes that have taken place relating to machine learning algorithms, which constitute major contributions to the machine learning process and help you to strengthen and master statistical interpretation across the areas of supervised, semi-supervised, and reinforcement learning. Once the core concepts of an algorithm have been covered, you’ll explore real-world examples based on the most diffused libraries, such as scikit-learn, NLTK, TensorFlow, and Keras. You will discover new topics such as principal component analysis (PCA), independent component analysis (ICA), Bayesian regression, discriminant analysis, advanced clustering, and gaussian mixture. By the end of this book, you will have studied machine learning algorithms and be able to put them into production to make your machine learning applications more innovative.
Table of Contents (19 chapters)

Logistic regression

Even if called regression, this is a classification method that is based on the probability of a sample belonging to a class. As our probabilities must be continuous in and bounded between (0, 1), it's necessary to introduce a threshold function to filter the term z. As already done with linear regression, we can get rid of the extra parameter corresponding to the intercept by adding a 1 element at the end of each input vector:

In this way, we can consider a single parameter vector θ, containing m + 1 elements, and compute the z-value with a dot product:

Now, let's suppose we introduce the probability p(xi) that an element belongs to class 1. Clearly, the same element belongs to class 0 with a probability 1 - p(xi). Logistic regression is mainly based on the idea of modeling the odds of belonging to class 1 using an exponential function...