We quantify the dynamical implications of the small-world phenomenon. We consider the generic synchronization of oscillator networks of arbitrary topology, and link the linear stability of the synchronous state to an algebraic condition of the Laplacian of the graph. We show numerically that the addition of random shortcuts produces improved network synchronizability. Further, we use a perturbation analysis to place the synchronization threshold in relation to the boundaries of the small-world region. Our results also show that small-worlds synchronize as efficiently as random graphs and hypercubes, and more so than standard constructive graphs.
PACS numbers:Recently, Watts and Strogatz [1] showed that the addition of a few long-range shortcuts to an otherwise locally connected lattice (the "pristine world") produces a sharp reduction of the average distance between arbitrary nodes. The ensuing semi-random lattice was denoted a small-world (SW) because the sudden appearance of short paths occurs early on, while the system is still relatively localized. This concept has wide appeal: the SW property seems to be a quantifiable characteristic of many real-world structures [1, 2, 3, 4], both human generated (social networks, WWW, power grid), or of biological origin (neural and biochemical networks).A spur of ongoing research [2] has concentrated on static and combinatoric properties [5,6,7,8,9, 10] of a tractable SW model [1,11]. Monasson [11] considered the SW effect on the distribution of eigenvalues of the connectivity matrix (the graph Laplacian) which specifies the coupling between nodes-a relevant topic for polymer networks [12]. However, despite their central role in real-world networks, there are fewer studies of dynamical processes taking place on SW lattices. Among those, automata epidemics simulations [13] In this paper, we explicitly link the SW addition of random shortcuts to the synchronization of networks of coupled dynamical systems. This is an example of dynamics on networks-leaving aside the distinct problem of evolution of networks here. By using a generic synchronization formulation [17,18] to factor out the connectivity of the network, we identify the synchronization threshold with an algebraic condition of the graph Laplacian. Through numerics and analysis, we quantify how the SW scheme improves the synchronizability of the pristine world, mainly as a result of the steep increase of the first-non-zero eigenvalue (FNZE). The synchronization threshold is found to lie in the SW region [3, 13], but does not coincide with its onset-it can in fact be linked to the effective randomization that ends SW. Within this framework, we show that the synchronization efficiency of semi-random SW networks is higher than standard deterministic graphs, and comparable to both fully random and ideal constructive graphs.Consider n identical dynamical systems (placed at the nodes of a graph) that are linearly and symmetrically coupled (as represented by the edges of the undirected graph) with global coupling strengt...