Sotirios Nikoloutsopoulos

PhD in Artificial Intelligence
Athens University of Economics and Business

I am a Machine Learning Researcher holding a PhD in Artificial Intelligence from the Athens University of Economics and Business, supervised by Michalis Titsias (Google DeepMind), Stavros Toumpis, and Iordanis Koutsopoulos. My research focuses on developing scalable Federated, Continual, and Meta-Learning algorithms designed to operate under decentralized, dynamic, and data-limited conditions.

Recently, I completed my military service as a Second Lieutenant and Researcher at the Hellenic Research Technological Development and Innovation Center (KETAK). My academic background spans computer science and data science, and I am currently expanding my theoretical foundations through a BSc in Mathematics at the National and Kapodistrian University of Athens.

Interests

  • Federated Learning
  • Continual Learning
  • Meta-Learning
  • Reinforcement Learning
  • Geometric Deep Learning
  • Probabilistic Machine Learning

Research

Multi-task learning, decentralized learning systems, and probabilistic methods for machine learning.

About Me

Sotirios Nikoloutsopoulos

Following the completion of my doctoral studies, I fulfilled my mandatory military service as a Second Lieutenant (Reserve Officer) in the Hellenic Army.

During this period, I was assigned to the Hellenic Research Technological Development and Innovation Center (KETAK). In this capacity, I continued to work as a Researcher, applying my expertise in Artificial Intelligence.

Technical Skills
Languages
Python, C/C++, Java, C#, R, Matlab, PHP, JavaScript, SQL
ML Frameworks
PyTorch, TensorFlow, JAX, Keras
Dev Tools
Git, Docker, LaTeX
3D & Design
Fusion 360, 3D Printing, Clip Studio Paint

Experience

Researcher (Military Service) - KETAK
Apr 2025 - Mar 2026
Served as a Second Lieutenant and Machine Learning Researcher at the Hellenic Research Technological Development and Innovation Center.
Researcher - AUEB
May 2021 - Apr 2023
Researcher in the project "Holistic and foundational resource allocation framework for optimized and impactful edge computing services (LeadingEdge)".
Software Engineer - Human Brain Project
Jan 2018 - Dec 2020
  • Setup LORIS for hospitals joining the Medical Informatics Platform.
  • Worked on Query rewriting for Ontology Based Data Access.

Education

2024 - Present
BSc in Mathematics
National & Kapodistrian University of Athens
2012 - 2016
BSc in Computer Science
University of Piraeus
Grade: 9.2 / 10.0
  • Distinction: Valedictorian (Graduated Top of the Class / Reading the Oath)
  • Thesis: "OCR for Trading Card Games"
  • Supervisor: Aggelos Pikrakis

Teaching Experience

Athens University of Economics and Business

Served as a Teaching Assistant for one course per semester throughout my doctoral studies.

Machine Learning
  • Spring 2019, 2020, 2021
  • Fall 2022
Probability & Mathematics
  • Probability: Spring 2022, 2024
  • Mathematics I: Fall 2023
  • Computational Mathematics: Fall 2020
Computer Science
  • Intro to Computer Programming: Fall 2019
  • Operating Systems: Spring 2018

Honors & Awards

  • Scholarship Recipient (2019)
    1st International Summer School on Artificial Intelligence and Games.
  • Valedictorian (2016)
    Graduated 1st in the class (GPA: 9.2/10) and delivered the graduation oath, University of Piraeus.
  • Deputy Team Member (2009)
    Junior Balkan Olympiad of Informatics.

Outreach

Volunteering & Mentorship

I have participated in the following voluntary teaching and educational initiatives:

  • Competitive Programming Seminars (UniPi):
    Co-organized and taught a series of algorithmic problem-solving workshops for undergraduate students, in collaboration with Ioannis Tasoulas.
    View Materials
  • JBOI Trainer: Taught Data Structures to junior students preparing for the Junior Balkan Olympiad in Informatics (JBOI).
  • National Competition Invigilator: Served as a voluntary proctor for the Panhellenic Competition in Informatics (PDP).

Publications

Sotirios Nikoloutsopoulos, Iordanis Koutsopoulos, Michalis Titsias (2025).
Personalized Federated Learning with Exact Stochastic Gradient Descent .
Applied Intelligence (Springer), Volume 55, article number 1123.
PDF
Sotirios Nikoloutsopoulos, Iordanis Koutsopoulos, Michalis Titsias (2024).
Kullback-Leibler Reservoir Sampling for Fairness in Continual Learning .
IEEE International Conference on Machine Learning for Communication and Networking (ICMLCN), Stockholm.
PDF
Apostolos G. Katsafados, Sotirios Nikoloutsopoulos, George N. Leledakis (2023).
Twitter sentiment and stock market: a COVID-19 analysis .
Journal of Economic Studies (Emerald).
PDF
Sotirios Nikoloutsopoulos, Iordanis Koutsopoulos, Michalis Titsias (2023).
Personalized Federated Learning with Exact Distributed Stochastic Gradient Descent Updates .
Adaptive and Learning Agents Workshop at AAMAS, London, UK.
PDF
Sotirios Nikoloutsopoulos, Iordanis Koutsopoulos, Michalis Titsias (2022).
Online Continual Learning from Imbalanced Data with Kullback-Leibler-loss based replay buffer updates .
NeurIPS 2022 Workshop on Human in the Loop Learning (HiLL), New Orleans.
PDF
Michalis K. Titsias, Francisco J. R. Ruiz, Sotirios Nikoloutsopoulos, Alexandre Galashov (2021).
Information Theoretic Meta Learning with Gaussian Processes .
Proceedings of the Thirty-Seventh Conference on Uncertainty in Artificial Intelligence (UAI 2021).
PDF
Michalis Titsias, Sotirios Nikoloutsopoulos (2018).
Bayesian Transfer Reinforcement Learning with Prior Knowledge Rules .
arXiv preprint arXiv:1810.00468.
PDF

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