# What is a graph?

by Stephen M. Walker II, Co-Founder / CEO

## What is a graph?

A graph is a mathematical structure that consists of nodes (also called vertices) and edges connecting them. It can be used to represent relationships between objects or data points, making it useful in various fields such as computer science, social networks, and transportation systems. Graphs can be directed or undirected, weighted or unweighted, and cyclic or acyclic, depending on the nature of the connections between nodes.

## What are the components of a graph?

The components of a graph are its nodes (vertices) and edges. Nodes represent objects or data points, while edges represent relationships between them. In a directed graph, each edge has an orientation indicating the direction of the relationship, while in an undirected graph, edges have no orientation. Weighted graphs assign numerical values to edges, representing the strength or cost of the relationship, while unweighted graphs do not.

## What are the properties of a graph?

The properties of a graph include its order (number of nodes), size (number of edges), degree (number of edges connected to a node), and connectivity (ability to reach all other nodes from any given node). Other important properties include cycle detection, pathfinding, and clustering.

## How can a graph be represented?

A graph can be represented in various ways, including adjacency matrices, adjacency lists, and edge lists. In an adjacency matrix, each row and column represents a node, with a 1 indicating the presence of an edge between them and a 0 indicating its absence. In an adjacency list, each node is associated with a list of nodes it is connected to. In an edge list, each edge is represented as a pair of nodes it connects.

## What are the operations that can be performed on a graph?

Operations that can be performed on a graph include traversal (visiting all nodes in the graph), pathfinding (finding the shortest or most efficient path between two nodes), and clustering (grouping nodes based on their similarity). Other common operations include cycle detection, topological sorting, and graph coloring.

## More terms

### What is first-order logic?

First-order logic (FOL), also known as first-order predicate calculus or quantificational logic, is a system of formal logic that provides a way to formalize natural languages into a computable format. It is an extension of propositional logic, which is less expressive as it can only represent information as either true or false. In contrast, FOL allows the use of sentences that contain variables, enabling more complex representations and assertions of relationships among certain elements.

### Stephen Cole Kleene

Stephen Cole Kleene was an American mathematician and logician who made significant contributions to the theory of algorithms and recursive functions. He is known for the introduction of Kleene's recursion theorem and the Kleene star (or Kleene closure), a fundamental concept in formal language theory.