# Graph ML

At graphml.app, our mission is to provide a comprehensive platform for graph machine learning. We aim to empower researchers, developers, and data scientists with the tools and resources they need to explore, analyze, and model complex graph data. Our goal is to foster innovation and collaboration in the field of graph machine learning, and to make this powerful technology accessible to everyone. Whether you are an expert in the field or just getting started, graphml.app is the place to be for all your graph machine learning needs.

# /r/machinelearning Yearly

Introduction

Graph machine learning is a rapidly growing field that combines graph theory and machine learning techniques to analyze and make predictions on graph data. Graph data is a type of data that represents relationships between entities, such as social networks, biological networks, and transportation networks. Graph machine learning algorithms can be used to solve a wide range of problems, such as recommendation systems, fraud detection, and drug discovery. This cheat sheet provides an overview of the key concepts, topics, and categories related to graph machine learning.

Graph Theory

Graph theory is the mathematical study of graphs, which are mathematical structures that represent relationships between objects. A graph consists of a set of vertices (also called nodes) and a set of edges (also called links) that connect the vertices. Graph theory provides a framework for analyzing and understanding the properties of graphs, such as connectivity, centrality, and clustering.

Types of Graphs

There are several types of graphs, including directed graphs, undirected graphs, weighted graphs, and bipartite graphs.

• Directed graphs: In a directed graph, the edges have a direction, indicating the flow of information or influence between the vertices. Directed graphs are also called digraphs.
• Undirected graphs: In an undirected graph, the edges do not have a direction, indicating that the relationship between the vertices is symmetric.
• Weighted graphs: In a weighted graph, the edges have a weight or cost associated with them, indicating the strength or importance of the relationship between the vertices.
• Bipartite graphs: In a bipartite graph, the vertices can be divided into two disjoint sets, such that there are no edges between vertices within the same set.

Graph Representation

Graphs can be represented using several data structures, including adjacency matrices, adjacency lists, and edge lists.

• Adjacency matrix: An adjacency matrix is a square matrix that represents the connections between vertices in a graph. The rows and columns of the matrix correspond to the vertices, and the entries in the matrix indicate whether there is an edge between the corresponding vertices.
• Adjacency list: An adjacency list is a list of lists that represents the connections between vertices in a graph. Each vertex has a list of its neighboring vertices.
• Edge list: An edge list is a list of tuples that represents the edges in a graph. Each tuple contains the two vertices that are connected by the edge.

Graph Algorithms

There are several graph algorithms that can be used to analyze and manipulate graphs, including breadth-first search, depth-first search, shortest path algorithms, and clustering algorithms.

• Breadth-first search: Breadth-first search is a graph traversal algorithm that visits all the vertices in a graph in breadth-first order, starting from a given vertex. This algorithm can be used to find the shortest path between two vertices in an unweighted graph.
• Depth-first search: Depth-first search is a graph traversal algorithm that visits all the vertices in a graph in depth-first order, starting from a given vertex. This algorithm can be used to detect cycles in a graph.
• Shortest path algorithms: Shortest path algorithms are used to find the shortest path between two vertices in a graph. The most commonly used shortest path algorithms are Dijkstra's algorithm and the Bellman-Ford algorithm.
• Clustering algorithms: Clustering algorithms are used to group vertices in a graph based on their similarity. The most commonly used clustering algorithms are k-means clustering and spectral clustering.

Machine Learning

Machine learning is a field of study that focuses on developing algorithms that can learn from data and make predictions or decisions based on that data. Machine learning algorithms can be divided into three categories: supervised learning, unsupervised learning, and reinforcement learning.

• Supervised learning: Supervised learning is a type of machine learning where the algorithm is trained on labeled data, meaning that the input data is paired with the correct output. The goal of supervised learning is to learn a function that can map new input data to the correct output.
• Unsupervised learning: Unsupervised learning is a type of machine learning where the algorithm is trained on unlabeled data, meaning that the input data is not paired with the correct output. The goal of unsupervised learning is to discover patterns or structure in the data.
• Reinforcement learning: Reinforcement learning is a type of machine learning where the algorithm learns by interacting with an environment and receiving rewards or punishments based on its actions. The goal of reinforcement learning is to learn a policy that maximizes the cumulative reward over time.

Graph Machine Learning

Graph machine learning combines graph theory and machine learning techniques to analyze and make predictions on graph data. Graph machine learning algorithms can be divided into two categories: graph-based algorithms and node-based algorithms.

• Graph-based algorithms: Graph-based algorithms operate on the entire graph and are used to extract global features or properties of the graph. The most commonly used graph-based algorithms are graph convolutional networks (GCNs) and graph attention networks (GATs).
• Node-based algorithms: Node-based algorithms operate on individual nodes in the graph and are used to extract local features or properties of the nodes. The most commonly used node-based algorithms are node2vec and GraphSAGE.

Graph Convolutional Networks (GCNs)

Graph convolutional networks (GCNs) are a type of graph-based algorithm that uses convolutional neural networks (CNNs) to operate on graphs. GCNs are used to extract global features or properties of the graph, such as node embeddings or graph embeddings. The key idea behind GCNs is to use a convolutional operation to aggregate information from neighboring nodes and update the node embeddings.

Graph Attention Networks (GATs)

Graph attention networks (GATs) are a type of graph-based algorithm that uses attention mechanisms to operate on graphs. GATs are used to extract global features or properties of the graph, such as node embeddings or graph embeddings. The key idea behind GATs is to use attention mechanisms to weight the contributions of neighboring nodes and update the node embeddings.

Node2Vec

Node2vec is a type of node-based algorithm that uses random walks to generate node embeddings. Node2vec is used to extract local features or properties of the nodes, such as node similarity or node centrality. The key idea behind Node2vec is to use a biased random walk to explore the graph and generate node sequences, which are then used to train a skip-gram model to learn the node embeddings.

GraphSAGE

GraphSAGE is a type of node-based algorithm that uses a graph convolutional neural network to generate node embeddings. GraphSAGE is used to extract local features or properties of the nodes, such as node similarity or node centrality. The key idea behind GraphSAGE is to use a neighborhood aggregation function to aggregate information from neighboring nodes and update the node embeddings.

Applications of Graph Machine Learning

Graph machine learning has a wide range of applications, including recommendation systems, fraud detection, drug discovery, and social network analysis.

• Recommendation systems: Graph machine learning can be used to build recommendation systems that suggest items to users based on their preferences and the preferences of similar users.
• Fraud detection: Graph machine learning can be used to detect fraudulent behavior in financial transactions by analyzing the relationships between entities involved in the transactions.
• Drug discovery: Graph machine learning can be used to discover new drugs by analyzing the relationships between molecules and predicting their properties.
• Social network analysis: Graph machine learning can be used to analyze social networks and identify influential nodes or communities.

Conclusion

Graph machine learning is a rapidly growing field that combines graph theory and machine learning techniques to analyze and make predictions on graph data. This cheat sheet provides an overview of the key concepts, topics, and categories related to graph machine learning, including graph theory, graph representation, graph algorithms, machine learning, graph-based algorithms, node-based algorithms, and applications of graph machine learning. By understanding these concepts, you can start exploring the exciting world of graph machine learning and apply it to solve real-world problems.

### Common Terms, Definitions and Jargon

1. Graph: A collection of nodes and edges that represent relationships between them.
2. Node: A point in a graph that represents an entity or object.
3. Edge: A line connecting two nodes that represents a relationship between them.
4. Graph database: A database that stores data in the form of graphs.
5. Graph theory: The study of graphs and their properties.
6. Machine learning: A type of artificial intelligence that allows machines to learn from data and improve their performance over time.
7. Deep learning: A type of machine learning that uses neural networks to learn from data.
8. Neural network: A type of machine learning algorithm that is modeled after the structure of the human brain.
9. Supervised learning: A type of machine learning where the algorithm is trained on labeled data.
10. Unsupervised learning: A type of machine learning where the algorithm is trained on unlabeled data.
11. Reinforcement learning: A type of machine learning where the algorithm learns through trial and error.
12. Clustering: A type of unsupervised learning where the algorithm groups similar data points together.
13. Classification: A type of supervised learning where the algorithm predicts the class of a new data point.
14. Regression: A type of supervised learning where the algorithm predicts a continuous value.
15. Graph embedding: A technique for representing nodes in a graph as vectors in a high-dimensional space.
16. Node classification: A task in graph machine learning where the algorithm predicts the class of a node in a graph.
17. Link prediction: A task in graph machine learning where the algorithm predicts the likelihood of a new edge forming between two nodes in a graph.
18. Graph convolutional network (GCN): A type of neural network designed for graph data.
19. Graph attention network (GAT): A type of neural network that uses attention mechanisms to weight the importance of different nodes in a graph.
20. Graph autoencoder: A type of neural network that learns to encode and decode graphs.

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