archimedes-Artificial Intelligence, Data Science, Algorithms-greece

 
Artificial Intelligence
 
Data Science
 
Algorithms

[Archimedes Mechanism Design Theme invited talk]Learning in Budgeted Auctions with Spacing Objectives

Dates
2025-01-22 14:30 - 16:00
Venue
Artemidos 1 - Amphitheater
Title: Learning in Budgeted Auctions with Spacing Objectives

Speaker: Giannis Fikioris (PhD Student at Cornell University, USA)

Abstract: In many repeated auction settings, participants care not only about how frequently they win but also how their winnings are distributed over time. This problem arises in various practical domains where avoiding congested demand is crucial, such as online retail sales and compute services, as well as in advertising campaigns that require sustained visibility over time. We introduce a simple model of this phenomenon, modeling it as a budgeted auction where the value of a win is a concave function of the time since the last win. This implies that for a given number of wins, even spacing over time is optimal. The goal is to maximize and evenly space conversions rather than just wins.

We study the optimal policies for this setting in second-price auctions and offer learning algorithms for the bidders that achieve low regret against the optimal bidding policy in a Bayesian online setting. Our main result is a computationally efficient online learning algorithm that achieves O(sqrt(T)) regret. We achieve this by showing that an infinite-horizon Markov decision process (MDP) with the budget constraint in expectation is essentially equivalent to our problem, even when limiting that MDP to a very small number of states. The algorithm achieves low regret by learning a bidding policy that chooses bids as a function of the context and the system's state, which will be the time elapsed since the last win (or conversion).

Short Bio: Giannis Fikioris  is a 5th-year PhD student in the department of Computer Science at Cornell University, advised by Eva Tardos. Before that, he got his diploma from NTUA, advised by Dimitris Fotakis. His interests include mainly Algorithmic Game Theory and Online Learning. Specifically, he has worked on Online Learning with Constraints, Online Resource Allocation, and Repeated Budgeted Auctions. His PhD has been supported by the NDSEG fellowship, the Onassis Scholarship, and the Google PhD fellowship.


You can attend remotely via MS-Teams through:

https://teams.microsoft.com/l/meetup-join/19%3ameeting_NzE4MjZkZGItZWE3NS00NzQ5LTk0OTItNWMzMzE3NjdkYjU4%40thread.v2/0?context=%7b%22Tid%22%3a%226ae07702-c5f7-4f38-9b87-acad62a75d93%22%2c%22Oid%22%3a%22700280a8-c91f-41bd-9bf8-38b7959b4a6f%22%7d   







 
 

Vision

To position Greece as a leading player in AI and Data Science

image
image

Mission

To build an AI Excellence Hub in Greece where the international research community can connect, groundbreaking ideas can thrive, and the next generation of scientists emerges, shaping a brighter future for Greece and the world

 

Welcome to ARCHIMEDES, a vibrant research hub connecting the global AI and Data Science research community fostering groundbreaking research in Greece and beyond. Its dedicated core team, comprising lead researchers, affiliated researchers, Post-Docs, PhDs and interns, is committed to advancing basic and applied research in Artificial Intelligence and its supporting disciplines, including Algorithms, Statistics, Learning Theory, and Game Theory organized around 8 core research areas. By collaborating with Greek and Foreign Universities and Research Institutes, ARCHIMEDES disseminates its research findings fostering knowledge exchange and providing enriching opportunities for students. Leveraging AI to address real-world challenges, ARCHIMEDES promotes innovation within the Greek ecosystem and extends its societal impact. Established in January 2022, as a research unit of the Athena Research Center with support from the Committee Greece 2021, ARCHIMEDES is funded for its first four years by the EU Recovery and Resilience Facility (RRF).

 
 

NEWS

 
Archimedes Talk by Dimitris Giovanis on

Archimedes Talk by Dimitris Giovanis on "Learning the “Right” Space for Data-driven Modeling and Uncertainty Quantification in Complex / Multiscale Systems"

20 January 2026

On Wednesday 4 February, 2026, from 1:00 pm to 2:00 pm, at the Archimedes Amphitheatre (1 Artemidos Street, 15125, Marousi, Archimedes, Athena Research Center, Greece), Professor Dimitris Giovanis, Assistant Research Professor in the Department of Civil and Systems Engineering, The Johns Hopkins University, USA, and fellow of the Hopkins Extreme Materials Institute, a member of the Center on Artificial Intelligence for Materials in Extreme Environments, the Institute for Data Intensive Engineering and Science, the Johns Hopkins Mathematical Institute for Data Science, and the Data Science and AI Institute, will deliver an Archimedes talk on "Learning the “Right” Space for Data-driven Modeling and Uncertainty Quantification in Complex / Multiscale Systems."

Director Timos Sellis Moderates a Panel on AI and Health Policy

Director Timos Sellis Moderates a Panel on AI and Health Policy

8 January 2026

On Thursday, 11 December 2025, during the 2025 Panhellenic Congress on Health Economics and Policy, Professor Timos Sellis moderated an expert panel on ¨How AI May Transform Healthcare and Health Policies” and exchanged views with Professor Costas Athanassakis, Professor Theoklis Zaoutis, Dr. Georgios Papanastasiou, and Dr. Harietta Eleftherochorinou.

Archimedes Surpasses 300 Publications

Archimedes Surpasses 300 Publications

5 January 2026

Archimedes Unit of the Athena Research Center, Greece, is proud to announce that its researchers have published over 300 scientific publications in top-tier conferences (including NeurIPS, ICLR, ICML) and leading academic journals.

First Call for Papers of the Workshop on Dialects in NLP (LREC 2026)

First Call for Papers of the Workshop on Dialects in NLP (LREC 2026)

2 January 2026

First call for papers for the "Workshop on Dialects in NLP: A Resource Perspective" at the three-day Language Resources Association Conference (LREC) 2026. This workshopwill be held in conjunction with LREC 2026, Palma de Mallorca, Spain on 11, 12 and 16 May 2026. It is a hybrid event and attendance can be in person or online. 

Participation is Open for the 2026 ELLIS Winter School

Participation is Open for the 2026 ELLIS Winter School

27 December 2025

Archimedes Unit of the Athena Research Center, Greece, encourages participation in the "ELLIS Winter School 2026: AI for Earth System, Hazards, and Climate Extremes", taking place on March 16-20, 2026, at the National Technical University of Athens, Greece.

More news items here
 
 

The project “ARCHIMEDES Unit: Research in Artificial Intelligence, Data Science and Algorithms” with code OPS 5154714 is implemented by the National Recovery and Resilience Plan “Greece 2.0” and is funded by the European Union – NextGenerationEU.

greece2.0 eu_arch_logo_en

 

Stay connected! Subscribe to our mailing list by emailing sympa@lists.athenarc.gr
with the subject "subscribe archimedes-news Firstname LastName"
(replace with your details)