While labeled data is expensive to prepare, ever increasing amounts of unlabeled data is becoming
widely available. In order to adapt to this phenomenon, several semi-supervised learning (SSL)
algorithms, which learn from labeled as well as unlabeled data, have been developed. In a separate
line of work, researchers have started to realize that graphs provide a natural way to represent
data in a variety of domains. Graph-based SSL algorithms, which bring together these two lines
of work, have been shown to outperform the state-of-the-art in many applications in speech
processing, computer vision, natural language processing, and other areas of Artificial Intelligence.
Recognizing this promising and emerging area of research, this synthesis lecture focuses on graphbased
SSL algorithms (e.g., label propagation methods). Our hope is that after reading this book,
the reader will walk away with the following: (1) an in-depth knowledge of the current stateof-
the-art in graph-based SSL algorithms, and the ability to implement them; (2) the ability to
decide on the suitability of graph-based SSL methods for a problem; and (3) familiarity with
different applications where graph-based SSL methods have been successfully applied.
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