Infection S/I. The epidemic is seeded with one or more infected nodes. Thereafter, infection progresses via a contact network; the probability of a node becoming infected depends on the state of the nodes directly linked to it. The probability p of a susceptible node with k infectious contacts becoming infected in a small time interval Dt is pZ1Kexp(KtkDt). Here, t is the rate of infection spreading through a single contact between an infectious and a susceptible node.