# 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.

## Fighting epidemics with the maximum spectral subgraph

Summary: Recent developments in mathematical epidemiology have identified a relationship between the time to extinction of an epidemic spreading over a network and the spectral radius of the underlying graph i.e. the largest eigenvalue of its adjacency matrix. At the same time, new generation networking technologies such as NFV ...

## Reconfiguration Distribuée de Problèmes de Graphes

Summary: En théorie des graphes, un problème de configuration est le suivant : est-il possible d'aller d'une solution valide d'un problème à une autre, en passant par un chemin de solutions acceptables ? Quelle est la longueur minimale d'un chemin ? Quelle est la complexité ? Par exemple, un problème ...

## Some recent results on the integer linear programming formulation for the Max-Cut problem

Summary: Given an undirected graph G=(V,E) where the edges are weighted by an arbitrary cost vector c, a cut S in G associated with a node subset S is the edge subset of E which contains all the edges having exactly one end-node in S. The Maximum Cut ...

Translations: fr