A network is a mathematical object consisting of a set of points(called vertices or nodes)that are connected to each other in somefashion by lines (called edges). Turns out thissimple descriptioncorresponds to a bewildering array of systems in the real world, ranging from technological ones such as the Internet and WorldWide Web, biological networks such as that of connections of thenervous systems or blood vessels, food webs, protein interactions, infrastructural systems such as networks of roads, airports or the power-grid, to patterns of social acquaintance such as friendship, network...