First Contact

Let’s establish some of the terms we’ll use. First of all, when we talk about graphs, we obviously mean networks—not charts. Traditionally the term “graph” has referred to a diagram or plot of one quantity against another. This is the more widely understood sense of the term. But that’s not our concern here. We’ll be using it in its other sense of a data structure used to model relationships between things. That is, we have a set of things and another set of relationships between those things. Those two sets together constitute a graph. In its most ...