Hi, bonjour, yeia

Welcome to my personal web-page. I am Argyris Kalogeratos (Αργύρης Καλογεράτος), I come from Patras, Greece and my background is on Computer Science. My PhD was on the field of Machine Learning (Dept. of Computer Science and Engineering, University of Ioannina, Greece – 2013), under the supervision of Aristidis Likas.


Position: I am a permanent researcher at the Centre de Mathématiques et de Leurs Applications (CMLA), Ecole Normale Supérieure de Cachan (ENS Paris Saclay), France, and member of the Machine Learning and Massive Data Analysis (MLMDA) research group (head: Nicolas Vayatis).

Research focus: Principal researcher on ML on Graphs.

Research initiatives: I participate to the research activities of the ML Industrial Big Data Chair (CMLA team: Julien Audiffren, Mathilde Mougeot, Nicolas Vayatis). Among our industrial partners, there are ATOSWordline, SNCF, CEA, Michelin, Bertin Tech.



Past funding: My research position at CMLA has been funded in the past by the MORANE project (in collaboration with SNCF railway company) and the SODATECH project  (funded by the French state) for which I was the research coordinator and responsible for CMLA’s part. See more details at the “Projects” section.

Research opportunities

Contact me or another member of our ML group to know more about the possibility to join us at CMLA for an internship or a thesis.


  • New interns:
    • Alejandro de la Concha (M2 MVA, Apr – Sep) will work on multivariate signal segmentation.
    • Anthea Mérida (M2, Apr – Oct) will work on ensemble methods and random forests.
    • Amel Addala (M2, Mar – Aug) will work on a problem related to EDF’s power network.
    • Rafael Gromit and Blandine Galiay (L3 ENS Paris-Saclay, Apr – Jul) will work on sequential selection processes over graphs.
    • Vincent Laheurte and Ferdinand Campos (L3 ENS Paris-Saclay, Apr – Jul) will work on statistical homogeneity testing.
  • ICASSP 2019Learning Laplacian Matrix from Bandlimited Graph Signals, co-authored with Batiste Le Bars, Pierre Humbert, and Laurent Oudre, will appear in the IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP), 12 – 17 May, 2019 · Brighton, UK. [pdf available soon]
  • INFOCOM 2019A Probabilistic Framework to Node-level Anomaly Detection in Communication Networks, co-authored with Batiste Le Bars, will appear in the IEEE International Conference on Computer Communications 2019 (INFOCOM), 29 Apr – 2 May 2019, Paris, France. [288 papers accepted / 1464 submissions: 19.7% rate] [pdf][bib] Abstract

    In this paper we consider the task of detecting abnormal communication volume occurring at node-level in communication networks. The signal of the communication activity is modeled by means of a clique stream: each occurring communication event is instantaneous, and activates an undirected subgraph spanning over a set of equally participating nodes. We present a probabilistic framework to model and assess the communication volume observed at any single node. Specifically, we employ non-parametric regression to learn the probability that a node takes part in a certain event knowing the set of other nodes that are involved. On the top of that, we present a concentration inequality around the estimated volume of events in which a node could participate, which in turn allows us to build an efficient and interpretable anomaly scoring function. Finally, the superior performance of the proposed approach is empirically demonstrated in real-world sensor network data, as well as using synthetic communication activity that is in accordance with that latter setting.

  • TechReport – A new paper was released, as Technical Report, introducing and analyzing the “The Multi-Round Sequential Selection Problem. It is co-authored with M. Fekom, and N. Vayatis, September 2018. [pdf][arXiv link] Abstract

    In the Sequential Selection Problem (SSP), immediate and irrevocable decisions need to be made while candidates from a finite set are being examined one-by-one. The goal is to assign a limited number of b available jobs to the best possible candidates. Standard SSP variants begin with an empty selection set (cold-starting) and perform the selection process once (single-round), over a single candidate set. In this paper we introduce the Multi-round Sequential Selection Problem (MSSP) which launches a new round of sequential selection each time a new set of candidates becomes available. Each new round has at hand the output of the previous one, i.e. its b selected employees, and tries to update optimally that selection by reassigning each job at most once. Our setting allows changes to take place between two subsequent selection rounds: resignations of previously selected subjects or/and alterations of the quality score across the population. The challenge for a selection strategy is thus to efficiently adapt to such changes. For this novel problem we adopt a cutoff-based approach, where a precise number of candidates should be rejected first before starting to select. We set a rank-based objective of the process over the final job-to-employee assignment and we investigate analytically the optimal cutoff values with respect to the important parameters of the problem. Finally, we present experimental results that compare the efficiency of different selection strategies, as well as their convergence rates towards the optimal solution in the case of stationary score distributions.

  • Book ChapterInformation Diffusion and Rumor Spreading, A. Kalogeratos, K. Scaman, L. Corinzia, and N. Vayatis, chapter in the book Cooperative and Graph Signal Processing – Principles and Applications, eds. P.M. Djuric and C. Richard, Elsevier, 2018. [pdf][publisher link][bib] Abstract
    This chapter studies information cascades on social networks with a special focus on types of diffusion processes such as rumors and false news. The complex temporal dynamics of information cascades and rapid changes in user interests require flexible mathematical modeling to properly describe the diffusion dynamics. After mentioning the modeling advancements of recent decades, we get to modern models, such as the Information Cascade Model (ICM), that are indeed capable of describing such time-dependent user interests and are thus particularly suited to the analysis of information diffusion. We provide a theoretical analysis of ICM, relating the dynamics of the cascade to structural characteristics of the social network, and then use that analysis to design control policies capable of efficiently reducing the undesired diffusion. The presented framework for activity shaping is generic while enjoying a simple convex relaxation. Finally, we present an algorithm for the control of Continuous-Time Independent Cascades which is evaluated and compared against baseline and state-of-the art approaches through diffusion simulations on real and synthetic social networks.
  • TechReport – A short paper with preliminary results, entitled “Node-level Anomaly Detection in Communication Networks“, co-authored with Batiste Le Bars, will be presented on June at the 3rd Graph Signal Processing Workshop (GSP), 2018. Abstract
    In this paper we consider the task of the detection of abnormal communication volume, occurring at node-level in a communication network. We model the communication by means of a dynamic graph with edges related to an occurring communication event appearing instantaneously. We propose a statistical model for the communication volume recorded at a single node, in order to detect anomalies. Our approach is evaluated in real-world communication data.
  • Workshop Poster – part of our work with Mathilde Fekom on sequential selection processes will be presented as a poster will be presented at the Workshop on Multi-Armed Bandits and Learning Algorithms.
  • Workshop Talk – On the French German summer school on Transfer Learning, June 4-6 2018, ENS-Paris-Saclay.
  • New intern – Thales Loiola Raveli will be working on the modeling of transportation traffic (May – Aug 2018).
  • TechReport – A new paper was released as Technical Report. Its title is “A Spectral Method for Activity Shaping in Continuous-Time Information Cascades” and it is co-authored with K. Scaman, L. Corinzia, and N. Vayatis, Sep 15, 2017. [pdf][arXiv link] Abstract

    The Information Cascades Model captures dynamical properties of user activity in a social network. In this work, we develop a novel framework for activity shaping under the Continuous-Time Information Cascades Model which allows the administrator for local control actions by allocating targeted resources that can alter the spread of the process. Our framework employs the optimization of the spectral radius of the Hazard matrix, a quantity that has been shown to drive the maximum influence in a network, while enjoying a simple convex relaxation when used to minimize the influence of the cascade. In addition, use-cases such as quarantine and node immunization are discussed to highlight the generality of the proposed activity shaping framework. Finally, we present the NetShape influence minimization method which is compared favorably to baseline and state-of-the-art approaches through simulations on real social networks.

  • New PhD student – Mathilde Fekom, previously a Master student at CMLA, will continue with us to the PhD adventure (starting Sep. 2017), after obtaining a highly competitive scholarship from Université Paris Saclay.
  • New students – We welcome three new students in the ML on Networks theme of MLMDA group, Mathilde Fekom (MSc thesis), Matteo Neri (MSc thesis), and Marin Scalbert (MSc internship), that are going to be with us at CMLA this semester.
  • Invited Talk – A two-hours seminar talk on “Epidemics, Competition and Resource Management” was given in Paris at a Working Group on Machine Learning and Big Data of the French Ministry of Social Affairs and Health (organizer: Magali Beffy). The group is formed by scientists and researchers working on various organizations/institutions (Ministry of Health, INSEE, IRDES, Dauphine) – 25/1/2017.
  • MECO 2017 – Part of the ongoing work on behavioral epidemics and dynamic control done with Stefano Sarao, Kevin Scaman, and Nicolas Vayatis is going to be presented in a poster format by Stefano at the 42nd Middle European Cooperation in Statistical Physics (MECO), Feb 2017, Lyon, France.
  • ΑΑΑΙ 2017 Multivariate Hawkes Processes for Large-scale Inference“, co-authored with Rémi Lemonnier and Kevin Scaman, will appear in the 31st AAAI Conference on Artificial Intelligence (AAAI-17), San Francisco, CA, US. [638 papers accepted / 2,590 submissions : 24.63% rate] – [pdf][supplementary][poster]. Abstract

    In this paper, we present a framework for fitting multivariate Hawkes processes for large-scale problems both in the number of events in the observed history n and the number of event types d (i.e. dimensions). The proposed Low-Rank Hawkes Process (SLRHP) framework introduces a low-rank approximation of the kernel matrix that allows to perform the nonparametric learning of the d^2 triggering kernels using at most O(ndr^2) operations, where r is the rank of the approximation (r << d, n). This comes as a major improvement to the existing state-of-the-art inference algorithms that are in O(nd^2). Furthermore, the low-rank approximation allows SLRHP to learn representative patterns of interaction between event types, which is usually for the analysis of complex processes in real-world networks.

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Curriculum Vitae (updated on Sep 2018)