Bootstrap Percolation in Inhomogeneous, Directed Random Graphs - Nils Detering

Event Date: 

Wednesday, January 6, 2016 -
3:30pm to 5:00pm

Event Date Details: 

Refreshments served at 3:15pm

Event Location: 

  • South Hall 5607F

Event Price: 

Free

  • Department Seminar Series

Bootstrap percolation is a process that is used to model the spread of an infection on a given graph. In the model considered each vertex is equipped with an individual threshold. As soon as the number of infected neighbors exceeds that threshold, the vertex gets infected as well and remains so forever. We perform a thorough analysis of bootstrap percolation on a novel model of directed and inhomogeneous random graphs, where the distribution of the edges is specified by assigning two distinct weights to each vertex, describing the tendency of it to receive edges from or to send edges to other vertices. Under the assumption that the limiting degree distribution of the graph is integrable we determine the typical fraction of infected vertices. Our model allows us to study settings that were outside the reach of current methods, in particular the prominent case in which the degree distribution has an unbounded variance. Among other results, we quantify the notion of "systemic risk", that is, to what extent local adverse shocks can propagate to large parts of the graph through a cascade, and discover novel features that make graphs prone/resilient to initially small infections. We show how our results can be used to study default contagion in a financial network. Furthermore, we discuss several statistical aspects related to our model.