Noncrossing partitions, Bruhat order and the cluster complex

Philippe Biane (1) , Matthieu Josuat-Vergès (1)

1 LIGM - Laboratoire d'Informatique Gaspard-Monge

We introduce two order relations on finite Coxeter groups which refine the absolute and the Bruhat order, and establish some of their main properties. In particular we study the restriction of these orders to noncrossing partitions and show that the intervals for these orders can be enumerated in terms of the cluster complex. The properties of our orders permit to revisit several results in Coxeter combinatorics, such as the Chapoton triangles and how they are related, the enumera-tion of reflections with full support, the bijections between clusters and noncrossing partitions.

Mots clés: Noncrossing partitions; Bruhat order; cluster complex

Domaines: Combinatoire [math.CO]

Philippe Biane, Matthieu Josuat-Vergès. Noncrossing partitions, Bruhat order and the cluster complex. Annales de l'Institut Fourier, 2019, 69 (5), pp.2241-2289. ⟨10.5802/aif.3294⟩. ⟨hal-01687706⟩