A Model for Social Network Formation: Efficiency, Stability and Dynamics.

We introduce a simple network formation model for social networks. Agents are nodes, connecting to another agent by building a directed edge (or accepting a connection from another agent) has a cost, and reaching (or being reached by) other agents via short directed paths has a benefit; in effect, an agent wants to reach others quickly, but without the cost of directly connecting each and every one. We prove that asynchronous edge dynamics always converge to a stable network; in fact, for nontrivial ranges of parameters this convergence is fast. Moreover, the set of fixed points of the dynamics form a nontrivial class of networks. For the static game, we give classes of efficient networks for nontrivial parameter ranges and further study their stability. We close several problems, and leave many interesting ones open.