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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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DTSTART:20250330T010000
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DTSTART;TZID=Europe/Paris:20250422T104500
DTEND;TZID=Europe/Paris:20250422T114500
DTSTAMP:20260503T154712
CREATED:20250416T143631Z
LAST-MODIFIED:20250416T143631Z
UID:11824-1745318700-1745322300@www.greyc.fr
SUMMARY:Séminaire Algorithmique : Josselin Guéneron (GREYC) « Repeated Stochastic Coalition Formation: representations and algorithmic approaches »
DESCRIPTION:Coalition formation is a cooperative game theory framework in which a set of agents\, required to perform implicit or explicit tasks\, must be divided into subgroups (called coalitions)\, according to collective criteria and a utility function describing the utility of each coalition. This is equivalent to a problem of partitioning the set of agents. The classic problem is to find a coalition structure (i.e. partitioning) that maximizes social welfare (sum of the utilities generated by the coalitions). A number of algorithmic approaches exist\, based on the exploration of a representation of the solution space\, in the form of an exhaustive lattice or integer partitions. However\, the classical approach to coalition formation assumes that agents have perfect knowledge of the utilities of coalitions\, and that these are deterministic\, which is not representative of the actual application problems we may encounter. \nWe are therefore interested in exploring algorithmic solutions for a stochastic and repeated context of coalition formation\, where agents have no a priori knowledge of utilities\, which are now stochastic. In this context\, classical representations (lattices\, integer partitions) and algorithms show limitations. We are exploring approaches based on Monte-Carlo tree search methods\, as well as the search for a suitable representation.
URL:https://www.greyc.fr/event/seminaire-algorithmique-josselin-gueneron-greyc-repeated-stochastic-coalition-formation-representations-and-algorithmic-approaches/
LOCATION:Sciences 3- S3 351
CATEGORIES:Amacc,General,News,Séminaire Algo
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DTSTART;TZID=Europe/Paris:20250429T104500
DTEND;TZID=Europe/Paris:20250429T114500
DTSTAMP:20260503T154712
CREATED:20250416T143759Z
LAST-MODIFIED:20250416T143759Z
UID:11826-1745923500-1745927100@www.greyc.fr
SUMMARY:Séminaire Algorithmique : Nicolas Bitar (LAMFA\, Univ. Picardie)\, « Subshifts of finite type and quasi-isometries beyond groups »
DESCRIPTION:In 1964\, R. Berger proved the existence of strongly aperiodic subshifts of finite type (SFT) on $\mathbb{Z}^2$\, and used them to prove the undecidability of the Domino Problem. With the goal of understanding what aspects of $\mathbb{Z}^2$ account for this result\, there has been an effort in recent years to characterize the groups with undecidable Domino Problem\, and groups that admit strongly aperiodic SFTs. A key result in this direction is a result by Cohen that states that both the decidability of the Domino Problem and the existence of strongly aperiodic SFTs are quasi-isometry invariants for finitely presented groups. In this talk\, I will explain how to generalize this result to new structures called blueprints. I will show how this generalizes results from the literature that use structures other than groups\, and use the result to show that the Domino Problem for multidimensional geometric tilings is undecidable.\n\nThis is joint work with Sebastián Barbieri.
URL:https://www.greyc.fr/event/seminaire-algorithmique-nicolas-bitar-lamfa-univ-picardie-subshifts-of-finite-type-and-quasi-isometries-beyond-groups/
LOCATION:Sciences 3- S3 351
CATEGORIES:Amacc,General,News,Séminaire Algo
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