The Local h-Vector of the Cluster Subdivision of a Simplex
Séminaire lotharingien de combinatoire, Tome 66 (2011-2012)
Citer cet article
Voir la notice de l'acte provenant de la source Séminaire Lotharingien de Combinatoire website
The cluster complex \Delta(\Phi) is an abstract simplicial complex, introduced by Fomin and Zelevinsky for a finite root system \Phi. The positive part of \Delta(\Phi) naturally defines a simplicial subdivision of the simplex on the vertex set of simple roots of \Phi. The local h-vector of this subdivision, in the sense of Stanley, is computed and the corresponding \gamma-vector is shown to be nonnegative. Combinatorial interpretations to the entries of the local h-vector and the corresponding \gamma-vector are provided for the classical root systems, in terms of noncrossing partitions of types A and B. An analogous result is given for the barycentric subdivision of a simplex.