Séries génératrices et preuves d'intrinsèque ambiguïté

-- Florent Koechlin (LORIA Univ. Nancy) (LIX)

Cet exposé porte sur la connexion entre l'intrinsèque ambiguïté en théorie des langages formels, et les propriétés des séries génératrices des langages associés. Il est bien connu que les langages réguliers ont des séries génératrices rationnelles et que les séries génératrices des langages algébriques non ambigus sont algébriques. Dans ...

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 ...

Associaèdres cycliques et degrés intrinsèques des arborescences non-croisées

-- Germain Poullot (LIX)

Le polytope de pivot d'un polytope P est une généralisation de son polytope des chemins monotones qui vise a capturer le comportement de la "shadow vertex rule" (une règle de pivot importante en optimisation linéaire et dans le domaine des polytopes de fibre). Il a récemment été montré que ...

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 ...

Séminaire ouvert

-- Toute l'équipe (LIX, GALAC)

Lors d'un séminaire ouvert, le thème n'est pas décidé à l'avance. Tous les membres du séminaires sont invités à participer et peuvent proposer le jour même des interventions plus ou moins longues, des démos ou des questions ouvertes au reste de l'équipe.

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 ...

A realization of poset associahedra as sections of graph associahedra

-- Chiara Mantovani (LIX)

Poset associahedra are a family of convex polytopes introduced by Pavel Galashin in 2021, each one associated to a partially ordered set, that generalize the classical associahedron. Galashin describes the combinatorial structure of poset associahedra, and he realizes them as convex polytopes. However, his construction is not completely satisfactory. In ...

(q,t)-symmetry in triangular partitions

-- Loïc Le Mogne (LISN, Galac)

We study the \((q,t)\) enumeration of the Triangular Dyck paths, i.e. the sub-partitions of the so-called triangular partitions discussed by Bergeron and Mazin. This is a generalization of the general \((q,t)\) enumeration of Catalan objects. We present new combinatorial notions such as the triangular tableau and the ...

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