Tag: Team seminar

Proper vertex coloring with odd occurence - Probabilistic approach

-- Qiancheng Ouyang (LISN)

summary: In graph theory, a graph coloring is an assignment of colors to elements of a graph subject to certain constraints. A vertex coloring is said to be proper if any pair of two adjacent vertices are assigned distinct colors. For a graph G, the chromatic number χ(G) is ...

Some results on directed coloring

-- Thomas Bellitto (LIP6, Sorbonne University)

summary: Proper coloring of undirected graphs lies among the most studied problems in graph theory. It asks to color vertices while giving different colors to adjacent ones.
In 1982, Neumann-Lara introduced a generalization of this problem to directed graphs. When walking in an undirected graph, an undirected edge between two ...

Walking On A Line: finding S-adic walks in an ω-automaton

-- Pierre Béaur (LISN, Galac)

summary: At the heart of symbolic dynamics lies the study of languages, infinite words and the dynamical structures associated. We focus on two classical methods to generate such structures. The first one relies on substitutions, which are morphisms on words, by iterating one on an initial letter, and considering the ...

Realizing Geometrically s-Permutahedra via Flow Polytopes

-- Daniel Tamayo-Jimenez (LISN, Galac)

summary: In 2020, Ceballos and Pons defined s-decreasing trees with s being a weak composition. They described an order on these objects called the s-weak order which gives them the order structure of a lattice. They further conjectured that this structure could be realized geometrically as the 1-skeleton of a ...

Density of sphere packings: from coins to oranges

-- Daria Pchelina (LIPN, Université Paris 13)

summary: How to stack an infinite number of oranges to maximize the proportion of the covered space? Kepler conjectured that the "cannonball" packing is an optimal way to do it. This conjecture took almost 400 years to prove and the proof of Hales and Ferguson consists of 6 papers and ...

An introduction to twin-width in graphs via the study of highly inapproximable problems

-- Pierre Bergé (ISIMA, Université Clermont Auvergne)

summary: The goal of this seminar is to introduce the graph parameter "twin-width", defined by Bonnet et al. in 2020. The collection of graphs with bounded twin-width generalizes many well-known families of graphs : planar, bounded treewidth and cliquewidth, unit interval,... The first motivation behind this parameter was that FO-expressible NP-hard ...

TracInAD: Measuring Influence for Anomaly Detection

-- Hugo Thimonier (LISN, Galac)

summary: As with many other tasks, neural networks prove very effective for anomaly detection purposes. However, very few deep-learning models are suited for detecting anomalies on tabular datasets. This talk proposes a novel methodology to flag anomalies based on TracIn, an influence measure initially introduced for explicability purposes. The proposed ...

Éléments minimaux des régions de Shi

-- Balthazar Charles (LISN, Galac)

summary: L'arrangement de Shi, introduit en 1987 par J.-Y. Shi, est un arrangement d'hyperplans liés aux groupes de réflexions cristallographiques possédant de nombreuses propriétés intéressantes. En particulier, les régions définies par les hyperplans liés à un groupe W correspondent aux états d'un automate introduit par B ...

(q,t)-symmetry in triangular partitions

-- Loïc Le Mogne (LISN, Galac)

summary: The study of Dyck paths and parking functions combinatorics is a central piece of the Diagonal Harmonic Polynomials theory. It is the origin of many currents problems of algebraic combinatorics. Interactioncs between Dyck paths, parking functions, the Tamari lattice, symmetric functions and other fields of mathematics or physics have ...

Designing truthful mecanism

-- Victor Glaser (LISN, Galac)

summary: In this presentation, we will focus on the generalization of knapsack budgeting. Given a set of projects and a budget, each voter selects a subset of projects; we want to maximize social welfare. Different measures can describe this (maximizing the minimum utility of the players, maximizing the sum of ...

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