Abstract
In this chapter, we introduce a propagation source estimator under complete observations: a maximum likelihood source estimator (Rumor Center). According to Chap. 5, a complete observation presents the exact state for each node in the network at certain time t. This type of observation provides comprehensive knowledge of a transient status of the network. Initial research on propagation source identification focused on complete observations, such as Rumor Center, Dynamic Age, Minimum Description Length, etc. Among these methods, Rumor center is a widely used method. Many variations have been proposed based on this method, such as Local Rumor Center, Multiple Rumor Center, etc. Here, we present the details of the Rumor Center estimator. For the techniques involved in other methods under complete observations, readers could refer to Chap. 9 for details.