The next three chapters are about systems made up of components and connections between components. For example, in a social network, the components are people and connections represent friendships, business relationships, etc. In an ecological food web, the components are species and the connections represent predator-prey relationships.
In this chapter, we introduce NetworkX, a Python package for building models of these systems. We start with the Erdős-Rényi model, which has interesting mathematical properties. In the next chapter we move on to models that are more useful for explaining real-world systems.