scholarly journals A bijection between (bounded) dominant Shi regions and core partitions

2010 ◽  
Vol DMTCS Proceedings vol. AN,... (Proceedings) ◽  
Author(s):  
Susanna Fishel ◽  
Monica Vazirani
Keyword(s):  
Symmetric Group ◽  
Type A ◽  
Catalan Numbers ◽  
Natural Extensions ◽  
International Audience ◽  
Shi Arrangement

International audience It is well-known that Catalan numbers $C_n = \frac{1}{ n+1} \binom{2n}{n}$ count the number of dominant regions in the Shi arrangement of type $A$, and that they also count partitions which are both n-cores as well as $(n+1)$-cores. These concepts have natural extensions, which we call here the $m$-Catalan numbers and $m$-Shi arrangement. In this paper, we construct a bijection between dominant regions of the $m$-Shi arrangement and partitions which are both $n$-cores as well as $(mn+1)$-cores. We also modify our construction to produce a bijection between bounded dominant regions of the $m$-Shi arrangement and partitions which are both $n$-cores as well as $(mn-1)$-cores. The bijections are natural in the sense that they commute with the action of the affine symmetric group. Il est bien connu que les nombres de Catalan $C_n = \frac{1}{ n+1} \binom{2n}{n}$ comptent non seulement le nombre de régions dominantes dans le Shi arrangement de type $A$ mais aussi les partitions qui sont à la fois $n$-cœur et $(n+1)$-cœur. Ces concepts ont des extensions naturelles, que nous appelons ici les nombres $m$-Catalan et le $m$-Shi arrangement. Dans cet article, nous construisons une bijection entre régions dominantes du $m$-Shi arrangement et les partitions qui sont à la fois $n$-cœur et $(nm+1)$-coeur. Nous modifions également notre construction pour produire une bijection entre régions dominantes bornées du $m$-Shi arrangement et les partitions qui sont à la fois $n$-coeur et $(mn-1)$-cœur. Ces bijections sont naturelles dans le sens où elles commutent avec l'action du groupe affine symétrique.

scholarly journals The freeness of Ish arrangements

2015 ◽  
Vol DMTCS Proceedings, 27th... (Proceedings) ◽  
Author(s):  
Takuro Abe ◽  
Daisuke Suyama ◽  
Shuhei Tsujie
Keyword(s):  
Catalan Numbers ◽  
Sufficient Condition ◽  
Necessary And Sufficient Condition ◽  
Free Arrangement ◽  
International Audience ◽  
New Interpretation ◽  
Necessary And Sufficient ◽  
Shi Arrangement

International audience The Ish arrangement was introduced by Armstrong to give a new interpretation of the $q; t$-Catalan numbers of Garsia and Haiman. Armstrong and Rhoades showed that there are some striking similarities between the Shi arrangement and the Ish arrangement and posed some problems. One of them is whether the Ish arrangement is a free arrangement or not. In this paper, we verify that the Ish arrangement is supersolvable and hence free. Moreover, we give a necessary and sufficient condition for the deleted Ish arrangement to be free L’arrangement Ish a été introduit par Armstrong pour donner une nouvelle interprétation des nombres $q; t$-Catalan de Garsia et Haiman. Armstrong et Rhoades ont montré qu’il y avait des ressemblances frappantes entre l’arrangement Shi et l’arrangement Ish et ont posé des conjectures. L’une d’elles est de savoir si l’arrangement Ish est un arrangement libre ou pas. Dans cet article, nous vérifions que l’arrangement Ish est supersoluble et donc libre. De plus, on donne une condition nécessaire et suffisante pour que l’arrangement Ish réduit soit libre.

scholarly journals Matrix-Ball Construction of affine Robinson-Schensted correspondence

2020 ◽  
Vol DMTCS Proceedings, 28th... ◽  
Author(s):  
Michael Chmutov ◽  
Pavlo Pylyavskyy ◽  
Elena Yudovina
Keyword(s):  
Symmetric Group ◽  
Weyl Group ◽  
Type A ◽  
Group Symmetry ◽  
Dominant Weight ◽  
Dominance Condition ◽  
The Matrix ◽  
International Audience ◽  
Affine Type

International audience In his study of Kazhdan-Lusztig cells in affine type A, Shi has introduced an affine analog of Robinson- Schensted correspondence. We generalize the Matrix-Ball Construction of Viennot and Fulton to give a more combi- natorial realization of Shi's algorithm. As a biproduct, we also give a way to realize the affine correspondence via the usual Robinson-Schensted bumping algorithm. Next, inspired by Honeywill, we extend the algorithm to a bijection between extended affine symmetric group and triples (P, Q, ρ) where P and Q are tabloids and ρ is a dominant weight. The weights ρ get a natural interpretation in terms of the Affine Matrix-Ball Construction. Finally, we prove that fibers of the inverse map possess a Weyl group symmetry, explaining the dominance condition on weights.

scholarly journals Bijections between noncrossing and nonnesting partitions for classical reflection groups

2009 ◽  
Vol DMTCS Proceedings vol. AK,... (Proceedings) ◽  
Author(s):  
Alex Fink ◽  
Benjamin Iriarte Giraldo
Keyword(s):  
Type A ◽  
Reflection Group ◽  
Catalan Numbers ◽  
Reflection Groups ◽  
Generalized Catalan Numbers ◽  
Elementary Methods ◽  
International Audience ◽  
Type Sets

International audience We present $\textit{type preserving}$ bijections between noncrossing and nonnesting partitions for all classical reflection groups, answering a question of Athanasiadis and Reiner. The bijections for the abstract Coxeter types $B$, $C$ and $D$ are new in the literature. To find them we define, for every type, sets of statistics that are in bijection with noncrossing and nonnesting partitions, and this correspondence is established by means of elementary methods in all cases. The statistics can be then seen to be counted by the generalized Catalan numbers Cat$(W)$ when $W$ is a classical reflection group. In particular, the statistics of type $A$ appear as a new explicit example of objects that are counted by the classical Catalan numbers.

scholarly journals The Shi arrangement and the Ish arrangement

2011 ◽  
Vol DMTCS Proceedings vol. AO,... (Proceedings) ◽  
Author(s):  
Drew Armstrong ◽  
Brendon Rhoades
Keyword(s):  
Degrees Of Freedom ◽  
Type A ◽  
Grand Nombre ◽  
Set Partition ◽  
Affine Weyl Group ◽  
Nous Montrons ◽  
International Audience ◽  
New Interpretation ◽  
Arrangements Of Hyperplanes ◽  
Shi Arrangement

International audience This paper is about two arrangements of hyperplanes. The first — the Shi arrangement — was introduced by Jian-Yi Shi to describe the Kazhdan-Lusztig cells in the affine Weyl group of type A. The second — the Ish arrangement — was recently defined by the first author who used the two arrangements together to give a new interpretation of the q,t-Catalan numbers of Garsia and Haiman. In the present paper we will define a mysterious "combinatorial symmetry'' between the two arrangements and show that this symmetry preserves a great deal of information. For example, the Shi and Ish arrangements share the same characteristic polynomial, the same numbers of regions, bounded regions, dominant regions, regions with c "ceilings'' and d "degrees of freedom'', etc. Moreover, all of these results hold in the greater generality of "deleted'' Shi and Ish arrangements corresponding to an arbitrary subgraph of the complete graph. Our proofs are based on nice combinatorial labellings of Shi and Ish regions and a new set partition-valued statistic on these regions. Cet article traite de deux arrangements d'hyperplans. Le premier — arrangement Shi — a été introduit par Jian-Yi Shi pour décrire les cellules de Kazhdan-Lusztig du groupe de Weyl affine de type A. Le deuxième — arrangement Ish — a été récemment défini par le premier auteur pour donner une nouvelle interprétation des nombres q,t-Catalan de Garsia et Haiman. Ici nous définissons une mystérieuse "symétrie combinatoire" entre les deux arrangements et nous montrons que cette symétrie conserve un grand nombre d'informations. Par exemple, les arrangements Shi et Ish ont le même polynôme caractéristique, le même nombre de régions, de régions bornées, de régions dominantes, de régions avec c "plafonds'' et d "degrés de liberté'', etc. En outre, ces résultats se généralisent aux arrangements Shi et Ish "deleted'' correspondant à un sous-graphe arbitraire du graphe complet. Nos preuves reposent sur des étiquetages combinatoires des régions Shi et Ish, et sur une nouvelle statistique associée.

scholarly journals Bijections of dominant regions in the $m$-Shi arrangements of type $A$, $B$ and $C$

2015 ◽  
Vol DMTCS Proceedings, 27th... (Proceedings) ◽  
Author(s):  
Myrto Kallipoliti ◽  
Eleni Tzanaki
Keyword(s):  
Type A ◽  
Lattice Paths ◽  
Nous Montrons ◽  
International Audience ◽  
Shi Arrangement ◽  
Nous Utilisons

International audience In the present paper, the relation between the dominant regions in the $m$-Shi arrangement of types $B_n/C_n$, and those of the $m$-Shi arrangement of type $A_{n-1}$ is investigated. More precisely, it is shown explicitly how the sets $R^m(B_n)$ and $R^m(C_n)$, of dominant regions of the $m$-Shi arrangement of types $B_n$ and $C_n$ respectively, can be projected to the set $R^m(A_{n-1})$ of dominant regions of the $m$-Shi arrangement of type $A_{n-1}$. This is done by using two different viewpoints for the representative alcoves of these regions: the Shi tableaux and the abacus diagrams. Moreover, bijections between the sets $R^m(B_n)$, $R^m(C_n)$, and lattice paths inside a rectangle $n\times{mn}$ are provided. Dans cet article, nous étudions la relation entre les régions dominantes du $m$-arrangement de Shi de types $B_n/C_n$ et ceux du $m$-arrangement de Shi de type $A_{n-1}$. Plus précisément, nous montrons comment les ensembles $R^m(B_n)$ et $R^m(C_n)$, des régions dominantes du $m$ -arrangement de Shi de types $B_n$ et $C_n$ respectivement, peuvent être projetés sur l’ensemble $R^m(A_{n-1})$ des régions dominantes du $m$-arrangement de Shi de types $A_{n-1}$. Pour cela nous utilisons deux points de vue différents sur les alcôves représentatives de ces régions: les tableaux de Shi et les diagrammes d’abaques. De plus, nous fournissons des bijections entre les ensembles $R^m(B_n)$, $R^m(C_n)$, et les chemins à l’intérieur d’un rectangle $n\times{mn}$.

scholarly journals Coxeter-like complexes

2004 ◽  
Vol Vol. 6 no. 2 ◽  
Author(s):  
Eric Babson ◽  
Victor Reiner
Keyword(s):  
Symmetric Group ◽  
Type A ◽  
Cell Complex ◽  
Coxeter System ◽  
Coxeter Complex ◽  
Homology Groups ◽  
Finite Set ◽  
International Audience ◽  
Regular Cell Complex ◽  
Chessboard Complexes

International audience Motivated by the Coxeter complex associated to a Coxeter system (W,S), we introduce a simplicial regular cell complex Δ (G,S) with a G-action associated to any pair (G,S) where G is a group and S is a finite set of generators for G which is minimal with respect to inclusion. We examine the topology of Δ (G,S), and in particular the representations of G on its homology groups. We look closely at the case of the symmetric group S_n minimally generated by (not necessarily adjacent) transpositions, and their type-selected subcomplexes. These include not only the Coxeter complexes of type A, but also the well-studied chessboard complexes.

scholarly journals Counting Shi regions with a fixed separating wall

2011 ◽  
Vol DMTCS Proceedings vol. AO,... (Proceedings) ◽  
Author(s):  
Susanna Fishel ◽  
Eleni Tzanaki ◽  
Monica Vazirani
Keyword(s):  
Type A ◽  
Narayana Numbers ◽  
International Audience ◽  
Shi Arrangement

International audience Athanasiadis introduced separating walls for a region in the extended Shi arrangement and used them to generalize the Narayana numbers. In this paper, we fix a hyperplane in the extended Shi arrangement for type A and calculate the number of dominant regions which have the fixed hyperplane as a separating wall; that is, regions where the hyperplane supports a facet of the region and separates the region from the origin. Athanasiadis a introduit la notion d'hyperplan de séparation pour une région dans l'arrangement de Shi et l'a utilisée pour généraliser les numéros de Narayana. Dans cet article, nous fixons un hyperplan dans l'arrangement de Shi pour le type A et calculons le nombre de régions dominantes qui ont l'hyperplan fixe pour mur de séparation, c'est-à-dire les régions où l'hyperplan soutient une facette de la région et sépare la région de l'origine.

scholarly journals $q,t$-Fuß-Catalan numbers for complex reflection groups

2008 ◽  
Vol DMTCS Proceedings vol. AJ,... (Proceedings) ◽  
Author(s):  
Christian Stump
Keyword(s):  
Hilbert Series ◽  
Type A ◽  
Catalan Numbers ◽  
Finite Complex ◽  
Reflection Groups ◽  
Combinatorial Properties ◽  
Cherednik Algebras ◽  
Complex Reflection ◽  
Complex Reflection Groups ◽  
International Audience

International audience In type $A$, the $q,t$-Fuß-Catalan numbers $\mathrm{Cat}_n^{(m)}(q,t)$ can be defined as a bigraded Hilbert series of a module associated to the symmetric group $\mathcal{S}_n$. We generalize this construction to (finite) complex reflection groups and exhibit some nice conjectured algebraic and combinatorial properties of these polynomials in $q$ and $t$. Finally, we present an idea how these polynomials could be related to some graded Hilbert series of modules arising in the context of rational Cherednik algebras. This is work in progress. Dans le cas du type $A$, les $q,t$-nombres de Fuß-Catalan $\mathrm{Cat}_n^{(m)}(q,t)$ peuvent être définis comme la série de Hilbert bigraduée d'un certain module associé au groupe symétrique $\mathcal{S}_n$. Nous généralisons cette construction aux groupes de réflexion complexes (finis) et nous formulons de jolies propriétés (conjecturales) algébriques et combinatoires de ces polynômes en $q$ et $t$. Enfin, nous décrivons une idée sur la manière dont ces polynômes pourraient être liés à certaines séries de Hilbert de modules apparaissant dans le contexte des algèbres de Cherednik rationnelles. Ceci est un travail en cours.

scholarly journals Multi-cluster complexes

2012 ◽  
Vol DMTCS Proceedings vol. AR,... (Proceedings) ◽  
Author(s):  
Cesar Ceballos ◽  
Jean-Philippe Labbé ◽  
Christian Stump
Keyword(s):  
Coxeter Groups ◽  
Type A ◽  
Simplicial Complexes ◽  
Cluster Complex ◽  
Geometric Properties ◽  
Cluster Complexes ◽  
Combinatorial Description ◽  
Compatibility Relation ◽  
Positive Roots ◽  
International Audience

International audience We present a family of simplicial complexes called \emphmulti-cluster complexes. These complexes generalize the concept of cluster complexes, and extend the notion of multi-associahedra of types ${A}$ and ${B}$ to general finite Coxeter groups. We study combinatorial and geometric properties of these objects and, in particular, provide a simple combinatorial description of the compatibility relation among the set of almost positive roots in the cluster complex. Nous présentons une famille de complexes simpliciaux appelés \emphcomplexes des multi-amas. Ces complexes généralisent le concept de complexes des amas et étendent la notion de multi-associaèdre de type ${A}$ et ${B}$ aux groupes de Coxeter finis. Nous étudions des propriétés combinatoires et géométriques de ces objets et, en particulier nous fournissons une description combinatoire simple de la relation de compatibilité sur l'ensemble des racines presque positives du complexe des amas.

scholarly journals A Crystal on Decreasing Factorizations in the 0-Hecke Monoid

10.37236/9168 ◽  
2020 ◽  
Vol 27 (2) ◽  
Author(s):  
Jennifer Morse ◽  
Jianping Pan ◽  
Wencin Poh ◽  
Anne Schilling
Keyword(s):  
Crystal Structure ◽  
Symmetric Group ◽  
Type A ◽  
Young Tableaux

We introduce a type $A$ crystal structure on decreasing factorizations of fully-commu\-tative elements in the 0-Hecke monoid which we call $\star$-crystal. This crystal is a $K$-theoretic generalization of the crystal on decreasing factorizations in the symmetric group of the first and last author. We prove that under the residue map the $\star$-crystal intertwines with the crystal on set-valued tableaux recently introduced by Monical, Pechenik and Scrimshaw. We also define a new insertion from decreasing factorization to pairs of semistandard Young tableaux and prove several properties, such as its relation to the Hecke insertion and the uncrowding algorithm. The new insertion also intertwines with the crystal operators.

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