Introduction to the issue on adaptation and learning over complex networks

The topic of this special issue is timely and deals with a subject matter that has been receiving immense attention from various research communities, and not only within the signal processing community. Extensive research efforts on information processing over graphs exist within other fields such as statistics, computer science, optimization, control, economics, machine learning, biological sciences, and social sciences. Different fields tend to emphasize different aspects and challenges; nevertheless, opportunities for mutual cooperation are abundantly clear and the role that signal processing plays in this domain is of fundamental importance. This is because, in all these fields, there is growing interest in performing inference, learning, and optimization over graphs, such as deducing relationships from interconnections over social networks, modeling interactions among agents in biological networks, performing resource allocation distributively, passing information over networks, optimizing utility functions over graphs, adapting and learning over graphs, etc. Commonalities, and significant signal processing, run across all these applications. The articles in this special issue report on up-to-date advances in the broad area of information processing over graphs.