Estimating the Number of Solutions of Cardinality Constraints through range and roots Decompositions

International audienceThis paper introduces a systematic approach for estimating the number of solutions of cardinality constraints. A main difficulty of solutions counting on a specific constraint lies in the fact that it is, in general, at least as hard as developing the constraint and its propaga-tors, as it has been shown on alldifferent and gcc constraints. This paper introduces a probabilistic model to systematically estimate the number of solutions on a large family of cardinality constraints including alldifferent, nvalue, atmost, etc. Our approach is based on their decomposition into range and roots, and exhibits a general pattern to derive such estimates based on the edge density of the associated variable-value graph. Our theoretical result is finally implemented within the maxSD search heuristic, that aims at exploring first the area where there are likely more solutions

Parking Spaces

Let $W$ be a Weyl group with root lattice $Q$ and Coxeter number $h$. The elements of the finite torus $Q/(h+1)Q$ are called the $W$-{\sf parking functions}, and we call the permutation representation of $W$ on the set of $W$-parking functions the (standard) $W$-{\sf parking space}. Parking spaces have interesting connections to enumerative combinatorics, diagonal harmonics, and rational Cherednik algebras. In this paper we define two new $W$-parking spaces, called the {\sf noncrossing parking space} and the {\sf algebraic parking space}, with the following features: 1) They are defined more generally for real reflection groups. 2) They carry not just $W$-actions, but $W\times C$-actions, where $C$ is the cyclic subgroup of $W$ generated by a Coxeter element. 3) In the crystallographic case, both are isomorphic to the standard $W$-parking space. Our Main Conjecture is that the two new parking spaces are isomorphic to each other as permutation representations of $W\times C$. This conjecture ties together several threads in the Catalan combinatorics of finite reflection groups. We provide evidence for the conjecture, proofs of some special cases, and suggest further directions for the theory.Comment: 49 pages, 10 figures, Version to appear in Advances in Mathematic

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Estimer le nombre de solutions des contraintes de cardinalité grâce à leur décomposition range et roots

National audienceEn programmation par contraintes, le choix d’une heuristique de recherche plutôt qu’une autre dépend souvent du problème. Cependant il existe des heuristiques génériques utilisant plutôt des indicateurs sur la structure combinatoire du problème. Les heuristiques "Counting- Based", introduites par Pesant et al., font des choix basés sur une estimation du nombre de solutions restantes dans tel ou tel sous-arbre de l’arbre de recherche. Un inconvénient de ces heuristiques est qu’elles nécessitent des algorithmes de dénombrement spécifiques à chaque contrainte. Cette étude s’intéresse aux contraintes de cardinalité, dont alldifferent, atmost, nvalue, etc... Nous proposons une méthode de comptage de solutions pour les contraintes range et roots, introduites par Bessiere et al. Grâce à la décomposition des contraintes de cardinalité en contraintes range et roots, nous dérivons une méthode systématique de dénombrement de solutions pour la plupart de ces contraintes