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PRODID:-//GREYC UMR CNRS 6072 - Groupe de Recherche en Informatique, Image, et Instrumentation de Caen - ECPv5.7.0//NONSGML v1.0//EN
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X-WR-CALNAME:GREYC UMR CNRS 6072 - Groupe de Recherche en Informatique, Image, et Instrumentation de Caen
X-ORIGINAL-URL:https://www.greyc.fr
X-WR-CALDESC:évènements pour GREYC UMR CNRS 6072 - Groupe de Recherche en Informatique, Image, et Instrumentation de Caen
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TZID:Europe/Paris
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TZOFFSETFROM:+0100
TZOFFSETTO:+0200
TZNAME:CEST
DTSTART:20250330T010000
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TZOFFSETFROM:+0200
TZOFFSETTO:+0100
TZNAME:CET
DTSTART:20251026T010000
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BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20250603T104500
DTEND;TZID=Europe/Paris:20250603T114500
DTSTAMP:20260430T102617
CREATED:20250416T144229Z
LAST-MODIFIED:20250526T134922Z
UID:11834-1748947500-1748951100@www.greyc.fr
SUMMARY:Séminaire Algorithmique : « Graphs of Shortest Paths »\, Mehdi Naima (LIP6\, Sorbonne Univ.)
DESCRIPTION:In this talk\, we will explore graphs of shortest paths—directed acyclic graphs (DAGs) derived from shortest path traversals of a graph rooted at a fixed source. After establishing a precise definition of these structures\, we will examine methods for uniformly sampling them and investigate their typical shape. Along the way\, we will uncover interesting connections to bipartite graphs.
URL:https://www.greyc.fr/event/seminaire-algorithmique-mehdi-naima-lip6-sorbonne-univ/
LOCATION:Sciences 3- S3 351
CATEGORIES:Amacc,General,News,Séminaire Algo
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20250604T140000
DTEND;TZID=Europe/Paris:20250604T150000
DTSTAMP:20260430T102617
CREATED:20250520T084501Z
LAST-MODIFIED:20250520T084501Z
UID:11867-1749045600-1749049200@www.greyc.fr
SUMMARY:Neily Sanon - L’identification et la mesure des biais dans les systèmes de reconnaissance facial
DESCRIPTION:Facial recognition systems exhibit varying levels of performance depending on demographic characteristics such as gender\, age\, or ethnic origin. These biases\, extensively documented in empirical studies\, raise critical concerns regarding reliability\, fairness\, and ethical compliance. \nThis presentation will examine the underlying sources of these biases\, whether they stem from dataset composition\, algorithmic choices\, or intersectional factors. It will also explore the different evaluation methods used to quantify performance disparities across groups\, along with mitigation strategies that can be applied at various stages of the processing pipeline Particular attention will be given to emerging certification mechanisms\, as regulatory authorities begin to incorporate bias evaluation into their assessment and approval processes.
URL:https://www.greyc.fr/event/neily-sanon-lidentification-et-la-mesure-des-biais-dans-les-systemes-de-reconnaissance-facial/
LOCATION:Sciences 3- S3 351
CATEGORIES:General,News,Safe,Séminaire Cryptologie et sécurité
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20250610T104500
DTEND;TZID=Europe/Paris:20250610T114500
DTSTAMP:20260430T102617
CREATED:20250416T144328Z
LAST-MODIFIED:20250502T081035Z
UID:11836-1749552300-1749555900@www.greyc.fr
SUMMARY:Séminaire Algorithmique : « Fractional domatic number and minimum degree »\, Hugo Demaret (Ecole Polytechnique et GREYC)
DESCRIPTION:The domatic number of a graph G is the maximum number of pairwise disjoint dominating sets of G. We are interested in the LP-relaxation of this parameter\, which is called the fractional domatic number of G. We study its extremal value in the class of graphs of minimum degree d. The fractional domatic number of a graph of minimum degree d is always at most d+1\, and at least (1-o(1))d/ln d as d goes to infinity. This is asymptotically tight even within the class of split graphs. \nOur main result concerns the case d=2. We show that\, excluding 8 exceptional graphs\, the fractional domatic number of every connected graph of minimum degree at least 2 is at least 5/2. We also show that this bound cannot be improved if only finitely many graphs are excluded\, even when restricting to bipartite graphs of girth at least 6. This proves in a stronger sense a conjecture by Gadouleau\, Harms\, Mertzios\, and Zamaraev (2024). This also extends and generalises results from McCuaig and Shepherd (1989)\, from Fujita\, Kameda\, and Yamashita (2000)\, and from Abbas\, Egerstedt\, Liu\, Thomas\, and Whalen (2016). Finally\, we show that planar graphs of minimum degree at least 2 and girth at least g have fractional domatic number at least 3-O(1/g) as g goes to infinity.\nWe present these results and provide insights into the proof. \nThis is a joint work with Quentin Chuet\, Hoang La and François Pirot.
URL:https://www.greyc.fr/event/seminaire-algorithmique-hugo-demaret-ecole-polytechnique-et-greyc/
LOCATION:Sciences 3- S3 351
CATEGORIES:Amacc,General,News,Séminaire Algo
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20250611T140000
DTEND;TZID=Europe/Paris:20250611T150000
DTSTAMP:20260430T102617
CREATED:20250527T091248Z
LAST-MODIFIED:20250527T190334Z
UID:11874-1749650400-1749654000@www.greyc.fr
SUMMARY:Henry Bambury - Polytopes in the Fiat-Shamir with Aborts Paradigm
DESCRIPTION:Post-quantum digital signatures have sparked a lot of interest in the cryptographic community in recent years. Both the NIST-selected signature Dilithium and Heatae\, winner of the Korean PQC competition\, rely on hardness of lattice problems and employ the Fiat-Shamir with Aborts paradigm\, in which rejection sampling is used to eliminate a secret’s dependency on a given source distribution. The distribution used to conceal the secret has direct consequences on signature performances\, such as size\, speed and simplicity. Dilithium uses a simple hypercube uniform sampler\, while Haetae improves signature sizes by using a significantly more complex sampler based on Euclidean balls. In this work\, we propose a framework relying on uniform sampling in polytopes\, and use it to instantiate a new signature scheme: Patronus. Patronus acts as a tradeoff between both standards\, offering improved signature sizes compared to Dilithium\, while using a sampler that is much simpler than Haetae’s\, as it avoids the need for Gaussian sampling.
URL:https://www.greyc.fr/event/henry-bambury-polytopes-in-the-fiat-shamir-with-aborts-paradigm/
LOCATION:Sciences 3- S3 351
CATEGORIES:General,News,Safe,Séminaire Cryptologie et sécurité
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20250612T140000
DTEND;TZID=Europe/Paris:20250612T150000
DTSTAMP:20260430T102617
CREATED:20250526T121333Z
LAST-MODIFIED:20250526T121427Z
UID:11869-1749736800-1749740400@www.greyc.fr
SUMMARY:Séminaire Image : "Hierarchical decimation for graph learning"\, Stevan Stanovic
DESCRIPTION:Nous aurons le plaisir d’écouter Stevan Stanovic\, doctorant de l’équipe Image.\nIl donnera un séminaire IMAGE le jeudi 12 juin 2025 à 14h en salle de séminaire F-200. \nTitre : « Hierarchical decimation for graph learning » \nRésumé :\nThis presentation focuses on hierarchical pooling in graph neural networks (GNNs)\, a key operation aimed at reducing the size of graphs while preserving their relevant information. Existing methods typically rely either on selecting a subset of vertices\, discarding the others\, or on loosely constrained clustering\, which ignores the original graph structure. These approaches suffer from several limitations : loss of information\, lack of consideration for the original graph structure\, and excessive densification of the reduced graphs. Moreover\, deep GNNs face two major phenomena : over-smoothing\, where node representations tend to converge towards a predetermined representation regardless of their initial features\, and over-squashing\, which refers to the difficulty in efficiently propagating information across long distances within the graph. In this manuscript\, we propose several hierarchical pooling methods based on maximal independent sets\, which preserve the graph structure while maintaining vertex attributes. Additionally\, we provide a theoretical and empirical study of these approaches\, highlighting their positive impact on over-smoothing and over-squashing. Our experimental results not only confirm the value of using maximal independent sets for defining pooling operations but also demonstrate their crucial role in mitigating over-smoothing and over-squashing. \nKeywords: Graph neural networks\, Graph Pooling\, Graph decimation\, Maximal Independent Set\, Over-smoothing\, Over-squashing.
URL:https://www.greyc.fr/event/seminaire-image-hierarchical-decimation-for-graph-learning-stevan-stanovic/
LOCATION:ENSICAEN – Batiment F – Salle F-200\, 6 Bd Maréchal Juin\, Caen\, 14050\, France
CATEGORIES:General,Image,News,Seminaire Image
END:VEVENT
BEGIN:VEVENT
DTSTART;VALUE=DATE:20250616
DTEND;VALUE=DATE:20250621
DTSTAMP:20260430T102617
CREATED:20250604T100324Z
LAST-MODIFIED:20250604T100324Z
UID:11878-1750032000-1750463999@www.greyc.fr
SUMMARY:EJCIFM2025 : Ecole Jeunes Chercheureuses en Informatique Fondamentale et ses Mathématiques
DESCRIPTION:L’objectif principal de cette école est de participer à une éducation de haut niveau pour les jeunes doctorants\, complémentaire de celle de leurs universités. Cela peut être une mise à jour dans certains domaines de leurs recherches\, ou aussi une ouverture vers de nouveaux sujets. En leur présentant l’état de la technique sur des sujets proches de leur spécialité\, nous leur apportons des outils pour mieux s’adapter à divers environnements (utile par exemple avant de passer en postdoc)\, et contribuons à favoriser leur mobilité. \nPour plus d’informations : https://ejcifm2025.sciencesconf.org/
URL:https://www.greyc.fr/event/ejcifm2025-ecole-jeunes-chercheureuses-en-informatique-fondamentale-et-ses-mathematiques/
LOCATION:Sciences 3\, Université\, Caen\, Bâtiment Sciences 3\, Caen\, France
CATEGORIES:Amacc,General,Mad,News
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20250618T140000
DTEND;TZID=Europe/Paris:20250618T150000
DTSTAMP:20260430T102617
CREATED:20250611T114554Z
LAST-MODIFIED:20250611T114554Z
UID:11889-1750255200-1750258800@www.greyc.fr
SUMMARY:Alban Gilard - Computation of the Hilbert Series for the Support-Minors Modeling of the MinRank Problem
DESCRIPTION:The MinRank problem is a simple linear algebra problem: given matrices with coefficients in a field\, find a non trivial linear combina- tion of the matrices that has a small rank. There are several algebraic modeling of the problem. The main ones are: the Kipnis-Shamir modeling\, the Minors modeling and the Support-Minors modeling. The Minors modeling has already been studied a lot\, we know a precise analysis of the complexity of computing a Gröbner basis of the modeling\, through the computation of the exact Hilbert Series for a generic instance. For the Support-Minors modeling\, the first terms of the Hilbert Series were known since 2020\, based on an heuristic and experimental work. Here\, we provide a formula and a proof for the complete Hilbert Series of the Support Minors modeling for generic instances. This is done by adapting well known results on determinantal ideals to an ideal generated by a particular subset of the set of all minors of a matrix of variables. We then show that this ideal is generated by standard monomials having a particular shape\, and derive the Hilbert Series by counting the number of such standard monomials. Following the work done for the Minors Modeling\, we then transfer the properties of this particular determinantal ideal to ideals generated by the Support Minors system\, by adding generic forms. This work allows to make a precise comparison between the Minors and Support Minors modeling\, and a precise estimate of the complex- ity of solving MinRank instances for the parameters of the Mirath signature scheme that is currently at the second round of the NIST standardization process for Additional Digital Signature Schemes.
URL:https://www.greyc.fr/event/alban-gilard-computation-of-the-hilbert-series-for-the-support-minors-modeling-of-the-minrank-problem/
LOCATION:Sciences 3- S3 351
CATEGORIES:General,News,Safe,Séminaire Cryptologie et sécurité
END:VEVENT
BEGIN:VEVENT
DTSTART;VALUE=DATE:20250623
DTEND;VALUE=DATE:20250626
DTSTAMP:20260430T102617
CREATED:20250604T100756Z
LAST-MODIFIED:20250623T081155Z
UID:11881-1750636800-1750895999@www.greyc.fr
SUMMARY:Journées Nationales 2025 du GDR Sécurité Informatique
DESCRIPTION:Les journées auront lieu au GREYC à Caen les 23-24-25 juin 2025. \nPour plus d’informations : https://gdr-secu-jn2025.sciencesconf.org/
URL:https://www.greyc.fr/event/journees-nationales-2025-du-gdr-securite-informatique/
LOCATION:Sciences 3\, Université\, Caen\, Bâtiment Sciences 3\, Caen\, France
CATEGORIES:General,News
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Paris:20250626T080000
DTEND;TZID=Europe/Paris:20250626T170000
DTSTAMP:20260430T102617
CREATED:20250626T072940Z
LAST-MODIFIED:20250626T072940Z
UID:11897-1750924800-1750957200@www.greyc.fr
SUMMARY:Journée 2025 du laboratoire GREYC : 19 Juin 2025
DESCRIPTION:La journée 2025 du GREYC aura lieu à la CCI de Caen (1 Rue René Cassin\, 14280 Saint-Contest) le 21 Juin 2024. \nAu programme : présentations\, démonstrations ! \nInscriptions à https://tinyurl.com/GREYC2025 \nConsultez le programme \n 
URL:https://www.greyc.fr/event/journee-2025-du-laboratoire-greyc-19-juin-2025/
CATEGORIES:General,News
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