[TOC] 13 Unsupervised Learning 13.1 Unsupervised Learning_ Introduction 13.2 K-Means Algorithm 13.3 Optimization Objective 13.4 Random Initialization 13.5 Choosing the Number of Clusters 14 Dimensionality Reduction 14.1 Motivation I_ Data Compression 14.2 Motivation II_ Visualization 14.3 Principal Component Analysis Problem Formulation 14.4 Principal Component Analysis Algorithm 14.5 Reconstruction from Compressed Representation 14.6 Choosing the Number of Principal Components 14.7 Advice for Applying PCA