Decay towards the overall-healthy state in SIS epidemics on networks

The decay rate of SIS epidemics on the complete graph $K_{N}$ is computed analytically, based on a new, algebraic method to compute the second largest eigenvalue of a stochastic three-diagonal matrix up to arbitrary precision. The latter problem has been addressed around 1950, mainly via the theory of orthogonal polynomials and probability theory. The accurate determination of the second largest eigenvalue, also called the \emph{decay parameter}, has been an outstanding problem appearing in general birth-death processes and random walks. Application of our general framework to SIS epidemics shows that the maximum average lifetime of an SIS epidemics in any network with $N$ nodes is not larger (but tight for $K_{N}$) than E\left[ T\right] \sim\frac{1}{\delta}\frac{\frac{\tau}{\tau_{c}}\sqrt{2\pi}% }{\left( \frac{\tau}{\tau_{c}}-1\right) ^{2}}\frac{\exp\left( N\left\{ \log\frac{\tau}{\tau_{c}}+\frac{\tau_{c}}{\tau}-1\right\} \right) }{\sqrt {N}}=O\left( e^{N\ln\frac{\tau}{\tau_{c}}}\right) for large $N$ and for an effective infection rate $\tau=\frac{\beta}{\delta}$ above the epidemic threshold $\tau_{c}$. Our order estimate of $E\left[ T\right]$ sharpens the order estimate $E\left[ T\right] =O\left( e^{bN^{a}}\right)$ of Draief and Massouli\'{e} \cite{Draief_Massoulie}. Combining the lower bound results of Mountford \emph{et al.} \cite{Mountford2013} and our upper bound, we conclude that for almost all graphs, the average time to absorption for $\tau>\tau_{c}$ is $E\left[ T\right] =O\left( e^{c_{G}N}\right)$, where $c_{G}>0$ depends on the topological structure of the graph $G$ and $\tau$

Die-out Probability in SIS Epidemic Processes on Networks

An accurate approximate formula of the die-out probability in a SIS epidemic process on a network is proposed. The formula contains only three essential parameters: the largest eigenvalue of the adjacency matrix of the network, the effective infection rate of the virus, and the initial number of infected nodes in the network. The die-out probability formula is compared with the exact die-out probability in complete graphs, Erd\H{o}s-R\'enyi graphs, and a power-law graph. Furthermore, as an example, the formula is applied to the $N$-Intertwined Mean-Field Approximation, to explicitly incorporate the die-out.Comment: Version2: 10 figures, 11 pagers. Corrected typos; simulation results of ER graphs and a power-law graph are added. Accepted by the 5th International Workshop on Complex Networks and their Applications, November 30 - December 02, 2016, Milan, Ital

Predicting Dynamics on Networks Hardly Depends on the Topology

Processes on networks consist of two interdependent parts: the network topology, consisting of the links between nodes, and the dynamics, specified by some governing equations. This work considers the prediction of the future dynamics on an unknown network, based on past observations of the dynamics. For a general class of governing equations, we propose a prediction algorithm which infers the network as an intermediate step. Inferring the network is impossible in practice, due to a dramatically ill-conditioned linear system. Surprisingly, a highly accurate prediction of the dynamics is possible nonetheless: Even though the inferred network has no topological similarity with the true network, both networks result in practically the same future dynamics

Exact Coupling Threshold for Structural Transition in Interconnected Networks

Interconnected networks are mathematical representation of systems where two or more simple networks are coupled to each other. Depending on the coupling weight between the two components, the interconnected network can function in two regimes: one where the two networks are structurally distinguishable, and one where they are not. The coupling threshold--denoting this structural transition--is one of the most crucial concepts in interconnected networks. Yet, current information about the coupling threshold is limited. This letter presents an analytical expression for the exact value of the coupling threshold and outlines network interrelation implications