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Community structure in complex networks

Complex systems typically display a modular structure, as modules are easier to assemble than the individual units of the system, and more resilient to failures. In the network representation of complex systems,
modules, or communities, appear as subgraphs whose nodes have an appreciably larger probability to get connected to each other than to other nodes of the network. In this talk I will address three fundamental questions: How is community structure generated? How to detect it? How to test the performance of community detection algorithms? I will show that communities emerge naturally in growing network models favoring triadic closure, a mechanism necessary to implement for the generation of large classes of systems, like e.g. social networks. I will discuss the limits of the most popular class of clustering algorithms, those based on the optimization of a global quality function, like modularity maximization. Testing algorithms is probably the single most important issue of network community detection, as it implicitly involves the concept of community,
which is still controversial. I will discuss the importance of using realistic benchmark graphs with built-in community structure.


Prof Santo Fortunato  received his PhD in Theoretical Physics in 2000 at the Department of Physics of the University of Bielefeld, Germany, working on lattice gauge theories, percolation and phenomenology of heavy-ion collisions. He switched to complexity science in 2004, and from 2005 till 2007 he was a postdoctoral researcher at the School of Informatics, Computing, and Engineering of Indiana University, working in the group of Alessandro Vespignani.

From 2007 till 2011 he was at ISI Foundation in Turin, Italy, first as research scientist then as a scientific leader.

 In 2011 he became Associate Professor and then Professor in Complex Systems at the School of Science of Aalto University , Finland.

 Since August 2016 he has been  professor at the School of Informatics, Computing, and Engineering.