# Graph Theory

The main focus is on structural and algorithmic point of views. The team established expertise includes problems such as finding large cycles in a given graph, graph colorings, covering problems, and extremal graph theory. For example, some team members are particularly interested in Thomassen’s conjecture: Every 4-connected line graph is Hamiltonian. Finding sufficient and computationally tractable conditions for a graph to be Hamiltonian is of significant importance from both theoretical and algorithmic viewpoints as Hamiltonicity is an NP-hard problem.

Generalization of such problems has also been recently considered for edge- or vertex-colored graphs. For example, one may look for properly colored spanning trees in an edge- or a vertex-colored graph. Alternatively, one may look for a dominating set in a vertex colored graph having at least one vertex from each color. Beside their theoretical interest, these extensions have applications in areas including biocomputing and web problems.

Many of the questions we consider can be stated in terms of (integer) linear optimization that is an expertise of new members of the team with research interests focusing on the combinatorial, computational, and geometric aspects of linear optimization. In this regard the aim would be to investigate recent results illustrating the significant interconnection between the most computationally successful algorithms for linear optimization and its generalizations, and the geometric and combinatorial structure of the input. Ideally, the deeper theoretical understanding will ultimately lead to increasingly efficient algorithms. Most of our research collaborations involve French research groups including LaBRI, LIRMM, LIAFA, and LIMOS as well as research groups in Europe, North America, China, Japan, India and South America.

## Reconstruction de graphes via des requêtes sur les triplets

summary: Considérons un oracle disposant d'un graphe labellisé caché. L'objectif de la reconstruction de graphes est de retrouver ce graphe caché en interrogeant l'oracle avec certains types de requêtes. Les requêtes que nous examinons portent sur des triplets de sommets du graphe, plus précisément, sur la structure ...

## Fractional domatic number and minimum degree

summary: We present a study of a graph parameter in graph theory, named the fractional domatic number. A dominating set in a graph is a set of vertices such that every vertex outside the set is adjacent to a vertex in the set. The domatic number of a graph is ...

## Recent Advances in Distributed Coloring

summary: The study of distributed graph algorithms aims to understand the limitations inherent to local computations. In a seminal paper, Linial (1992, SIAM J. Computing) introduced the LOCAL model to formalize this question. In this model, the input graph is seen as a communication network where vertices are computers. They ...

Translations: fr