Social Networks and Online Markets

Academic year 2022–2023

We are surrounded by networks. The Internet, one of the most advanced artifacts ever created by mankind, is the paradigmatic example of a "network of networks" with unprecedented technological, economical and social ramifications. Online social networks have become a major driving phenomenon on the web since the Internet has expanded as to include users and their social systems in its description and operation. Technological networks such as the cellular phone network or the energy grid support many aspects of our daily life. Moreover, there is a growing number of highly-popular user-centric applications in Internet that rely on social networks for mining and filtering information, for providing recommendations, as well as for ranking of documents and services. In this course we will present the design principles and the main structural properties and theoretical models of online social networks and technological networks, algorithms for data mining in social networks, and the basic network economic issues, with an eye towards the current research issues in the area.



The next exam dates are June 20 and July 6.

There have been some changes in the exam format; check below. You must have received an email with details.

For the part on online markets, you need to register to Google classroom

Remember to register your email; for details send an email to Aris.

Classes start on Monday, February 20.


Topics that we will cover

  • Properties of social networks
  • Models for social networks
  • Community detection
  • Spectral techniques for community detection
  • Cascading behavior in social networks and epidemics
  • Influence maximization and viral marketing
  • Influence and homophily
  • Machine learning on graphs
  • Introduction to Game Theory and Computational issues
  • Price of Anarchy and Selfish Routing
  • Stable matching, Markets, Competitive equilibria
  • Sponsored Search Auctions, VCG, Revenue Maximization
  • Voting and Fair division
  • Equilibria and Incentives in blockchains and cryptocurrencies



Aris Anagnostopoulos, Sapienza University of Rome

Stefano Leonardi, Sapienza University of Rome

Georgios Birmpas, Sapienza University of Rome


When and where:

Monday 15.00–17.00, Via Ariosto 25, Room A5

Wednesday 13.00–17.00, Via Ariosto 25, Room A3


Office hours

You can use the office hours for any question regarding the class material, general questions on networks, the meaning of life, pretty much anything. Send an email to the instructors for arrangement.


Textbook and references

The main textbook for the first part is the book Networks, Crowds, and Markets: Reasoning About a Highly Connected World, by David Easley and Jon Kleinberg.

The main textbook for the second part is the book Twenty Lectures on Algorithmic Game Theory, by Tim Roughgarden.

In addition, we will cover material from various other sources, which we will post online as the course proceeds.


Evaluation format (updated)

You will be evaluated for the two parts of the course (social networks, online markets) independently from each other, and your grade will be the average of the two parts. For each of them, you have the option of a project or a homework. For more details email the instructors, but you must have received an email. There is also the option of a written exam.




Date Topic Reading
February 20 Introduction to social networks and online markets, Properties of complex networks. Chapters 1, 2, slides
February 22 Properties of complex networks (cont.), homophily, the Erdős–Rényi random-graph model Chapter 4.0–4.1, notes
February 27 The small-world model, the preferential-attachment model Notes
March 1 The preferential-attachment model (cont.), epidemics, influence maximization Slides on epidemics and on influence maximization, paper by Kempe et al.
March 6 Influence maximization (cont.), influcence vs. correlation Slides on influence vs. correlation, paper by Anagnostopoulos et al.
March 8 Influence vs. correlation (cont.), densest subgraph Notes on Charikar's greedy algorithm for finding the densest subgraph
March 13 Community detection Notes on community detection
March 15 Community detection (cont.)
March 20 Community detection (cont.), node embeddings Chapters 3.0–3.1 of Graph Representation Learning by Hamilton
March 22 Classification, node embeddings based on random walks, introduction to neural networks Chapter 3.3.0 of Graph Representation Learning by Hamilton, papers on DeepWalk and node2vec; for NNs there are various sources online, for example, Chapter 6 of Deep Learning by Goodfellow, et al.
March 27 Graph neural networks There are a lot of resources on GNNs. I linke the chapter of The Science of Deep Learning by Drori, however it is not available online. A starting point could be this video although it does not talk about the concept of computation graph.
March 29 Lab on graph neural networks
April 1–end Online markets Google classroom



Collaboration policy (read carefully!): You can discuss with other students of the course about the homeworks and the projects. However, you must understand well your solutions and the final writeup must be yours and written in isolation. In addition, even though you may discuss about how you could implement an algorithm, what type of libraries to use, and so on, the final code must be yours. You may also consult the internet for information, as long as it does not reveal the solution. If a question asks you to design and implement an algorithm for a problem, it's fine if you find information about how to resolve a problem with character encoding, for example, but it is not fine if you search for the code or the algorithm for the problem you are being asked. For the homeworks and projects, you can talk with other students of the course about questions on the programming language, libraries, some API issue, and so on, but both the solutions and the programming must be yours. If we find out that you have violated the policy and you have copied in any way you will automatically fail. If you have any doubts about whether something is allowed or not, ask the instructor.