Graphs, graphs, graphs

This section will be a quick refresher on graphs and basic graph theory. If you’re not familiar with graphs – don’t worry – you can treat this section as a crash course on the topic.

Let’s start!

Graphs can be defined in multiple ways. You can think of them as discrete mathematical structures, abstract representations of real-world entities and relations between them, or computational data structures. What all of these perspectives have in common are the basic building blocks of graphs: nodes (also called vertices) and edges (links) that connect the nodes.

Types of graphs

We can divide graphs into types based on several attributes. Let’s discuss the ones that are the most relevant from the causal point of view.

Undirected versus directed

Directed graphs are graphs with directed edges, while undirected graphs have undirected edges. Figure 4.1 presents an example of a directed and undirected graph:

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