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.
Proper conflict-free colourings of graphs
summary: Given a graph \(G\) of maximum degree \(\Delta\), the proper colouring problem asks for the minimum number of colours that can be assigned to the vertices of \(G\) such that no pair of adjacent vertices are given the same colour; it is easy to show that at most \(\Delta ...
On the complexity of computing tree-partitions
summary: Tree-partitions are graph decompositions that correspond to mapping vertices to nodes of a tree in such a way that adjacent vertices in the graph are either mapped to adjacent nodes of the tree or to the same node. The width of a tree-partition is the maximum number of vertices ...
On the Structure of Potential Counterexamples to the Borodin-Kostochka Conjecture
summary: The Borodin-Kostochka conjecture, a long-standing problem in graph theory, asserts that every graph \(G\) with maximum degree \(\Delta \geq 9\) satisfies \(\chi(G) \leq max \{\Delta - 1, \omega(G)\}\) where \(\chi(G)\) and \(\omega(G)\) are respectively the chromatic number and the clique number of \(G\). While the conjecture ...
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