Building a graph is not enough; we also need the ability to search through it. To make it easier to build search algorithms, it is useful if we can represent the graph and its connections in a different way; adjacency matrix being one such representation. An adjacency matrix is a means of representing which vertices (or nodes) of a graph are adjacent to which other vertices.

He includes some sample code to extract the data from a graph (built with the PEAR Structures_Graph package) and create a basic "table" of information about each nodes' connections.

The Pear Structures_Graph package allows creating and manipulating graph data structures. It allows building of either directed or undirected graphs, with data and metadata stored in nodes. The library provides functions for graph traversing as well as for characteristic extraction from the graph topology.

After sharing the one-line install, he shows how to create some instances of the package's Nodes and how to connect them to a graph and link them to other nodes. He includes a few examples - a simpler one with multiple nodes joined in a directed graph, another showing how to associate data with a node and how to query the graph for node connections and testing to see if the graph is acyclic.