Ever since Kempe, Klienberg and Tardos (KKT) published their seminal paper on
maximizing the spread of influence in a social network, there has been
substantial work in this area. In the context of propagations in a social
graph, we can identify three orthogonal dimensions -- the number of seed nodes
activated at the beginning (known as budget), the (expected) number of
activated nodes at the end of the propagation (known as spread or coverage),
and the time taken for the propagation. We can constrain one or two of these
and try to optimize the third.