### A Propagation Engine Framework

, 2012

"... Constraint propagation is at the heart of constraint solvers. Two main trends co-exist: variable-oriented propagation engines and constraint-oriented propagation engines. Those two approaches ensure the same consistency level (generally AC) but their efficiency (computation time) can be quite diff ..."

Abstract
- Add to MetaCart

Constraint propagation is at the heart of constraint solvers. Two main trends co-exist: variable-oriented propagation engines and constraint-oriented propagation engines. Those two approaches ensure the same consistency level (generally AC) but their efficiency (computation time) can be quite different depending on the instance solved. It is usually accepted that there is no best approach in general, and modern constraint solvers only implement one. In this paper, we would like to go a step forward providing an adaptive propagation engine in order to broaden constraint solver flexibility. We first introduce an architecture based on event recorders that enables to naturally and efficiently compose state-of-the-art propagation schemas. Next, we show that recent features like propagator groups can be extended in order to accurately configure revision ordering within the propagation loop. Finally, we propose a solver independent language to enable the design of propagation engines on the fly. We validate our proposal with a reference

### Quadratic Direct Encoding vs. Linear Order Encoding A One-out-of-N Transformation on CNF

"... Abstract. The translation from finite CSPs into SAT has been studied intensively. Common encodings for variable domains are the compact, direct and order encoding. The direct encoding needs a quadratic number of clauses for encoding a domain in SAT whereas the order encoding uses only linearly many. ..."

Abstract
- Add to MetaCart

(Show Context)
Abstract. The translation from finite CSPs into SAT has been studied intensively. Common encodings for variable domains are the compact, direct and order encoding. The direct encoding needs a quadratic number of clauses for encoding a domain in SAT whereas the order encoding uses only linearly many. We introduce a conversion for domains from the direct encoding to the order encoding on the CNF level by extracting the encoded domains and replacing the related clauses by the order encoding and a mapping between them. The transformation keeps the model for the original formula and transforming domains with more than 8 elements results in less clauses in the formula. Experiments showed that our SAT solver riss can solve the transformed instances with domains greater than 7 from the SAT Competition 2009 Application with 3.4 % less run time. On 105 crafted instances riss could solve 55 instead of 58 instances, but the average run time decreased by 30 %. Results for PrecoSAT, clasp and march hi will be presented as well, showing that the transformation boosts the performance of CDCL solvers. 1

### Domaine: Algorithmique, programmation, logiciels et architectures

, 2011

"... apport de recherche ..."

(Show Context)
### option Artificial Intelligence

"... I would like to thank both my promoters Peter van Roy and Sabri Skhiri for their insightful comments, critics and advices about my work during the whole academic year. I also want to thank Boris Mejias for his continuous support and for pushing me to make a talk at FOSDEM 2011. This talk really help ..."

Abstract
- Add to MetaCart

(Show Context)
I would like to thank both my promoters Peter van Roy and Sabri Skhiri for their insightful comments, critics and advices about my work during the whole academic year. I also want to thank Boris Mejias for his continuous support and for pushing me to make a talk at FOSDEM 2011. This talk really helped moved forward my work by making it more public and brought back a lot of interesting feedback. Finally, I am grateful to Nam-Luc Tran for reading back and correcting a lot of errors. Contents

### Consistency of Constraint Networks Induced by Automaton-Based Constraint Specifications

"... Abstract. We discuss the consistency of constraints for which the set of solutions can be recognised by an automaton. Such an automaton induces a decomposition of the constraint into a conjunction of constraints. The so far most general result is that if the constraint hypergraph of such a decomposi ..."

Abstract
- Add to MetaCart

(Show Context)
Abstract. We discuss the consistency of constraints for which the set of solutions can be recognised by an automaton. Such an automaton induces a decomposition of the constraint into a conjunction of constraints. The so far most general result is that if the constraint hypergraph of such a decomposition is Berge-acyclic, then the decomposition provides hyperarc consistency. We focus on constraint networks that have α-acyclic or centred-cyclic hypergraph representations and show the necessary conditions to achieve hyper-arc consistency in these cases.

### DFA-based formulation for constraint negation?

"... Abstract. Global constraint design is a key success of CP for solving hard com-binatorial problems. Many works suggest that automaton-based definitions and filtering make easier the design of new global constraints. In this paper, from such a design, we present a preliminary work that gives an autom ..."

Abstract
- Add to MetaCart

(Show Context)
Abstract. Global constraint design is a key success of CP for solving hard com-binatorial problems. Many works suggest that automaton-based definitions and filtering make easier the design of new global constraints. In this paper, from such a design, we present a preliminary work that gives an automaton-based definition of the NEGATION of a global constraint. For a given global constraint C, the idea lies in giving operators for computing an automaton that recognizes only tuples that are not solution of C, and use the REGULAR global constraint to automat-ically reason on this automaton. We implemented this approach for automaton-based global constraints, including global_contiguity and ≤lex constraints, and got experimental results that show that their automatically computed negation is highly competitive with more syntactic transformations. 1

### Constraint Acquisition∗

"... Constraint programming is used to model and solve complex combina-torial problems. The modeling task requires some expertise in constraint programming. This requirement is a bottleneck to the broader uptake of constraint technology. Several approaches have been proposed to assist the non-expert user ..."

Abstract
- Add to MetaCart

(Show Context)
Constraint programming is used to model and solve complex combina-torial problems. The modeling task requires some expertise in constraint programming. This requirement is a bottleneck to the broader uptake of constraint technology. Several approaches have been proposed to assist the non-expert user in the modelling task. This paper presents the basic architecture for acquiring constraint networks from examples classified by the user. The theoretical questions raised by constraint acquisition are stated and their complexity is given. We then propose Conacq, a sys-tem that uses a concise representation of the learner’s version space into a clausal formula. Based on this logical representation, our architecture uses strategies for eliciting constraint networks in both the passive acquisition context, where the learner is only provided a pool of examples, and the active acquisition context, where the learner is allowed to ask membership queries to the user. The computational properties of our strategies are analyzed and their practical effectiveness is experimentally evaluated. 1

### Propagating Regular Counting Constraints

, 2014

"... Constraints over finite sequences of variables are ubiquitous in sequencing and timetabling. This led to general modelling techniques and generic propagators, often based on deterministic finite automata (DFA) and their extensions. We consider counter-DFAs (cDFA), which provide concise models for re ..."

Abstract
- Add to MetaCart

(Show Context)
Constraints over finite sequences of variables are ubiquitous in sequencing and timetabling. This led to general modelling techniques and generic propagators, often based on deterministic finite automata (DFA) and their extensions. We consider counter-DFAs (cDFA), which provide concise models for regular counting constraints, that is constraints over the number of times a regular-language pattern occurs in a sequence. We show how to enforce domain consistency in polynomial time for at-most and at-least regular counting constraints based on the frequent case of a cDFA with only accepting states and a single counter that can be increased by transitions. We also show that the satisfaction of exact regular counting constraints is NP-hard and that an incomplete propagator for ex-act regular counting constraints is faster and provides more pruning than the existing propagator from (Beldiceanu, Carlsson, and Petit 2004). Finally, by avoiding the unrolling of the cDFA used by COSTREGULAR, the space complexity reduces from O(n · |Σ | · |Q|) to O(n · (|Σ | + |Q|)), where Σ is the alphabet and Q the state set of the cDFA.

### Constraints manuscript No. (will be inserted by the editor) A Constraint-Based Local Search

"... the date of receipt and acceptance should be inserted later Abstract MiniZinc is a modelling language for combinatorial problems, which can then be solved by a solver provided in a backend. There are many backends, based on technologies such as constraint programming, integer programming, or Boolean ..."

Abstract
- Add to MetaCart

(Show Context)
the date of receipt and acceptance should be inserted later Abstract MiniZinc is a modelling language for combinatorial problems, which can then be solved by a solver provided in a backend. There are many backends, based on technologies such as constraint programming, integer programming, or Boolean satisfiability solving. However, to the best of our knowledge, there is currently no constraint-based local search (CBLS) backend. We discuss the challenges to develop such a backend and give an overview of the design of a CBLS backend for MiniZinc. Experimental results show that for some MiniZinc models, our CBLS backend, based on the OscaR/CBLS solver, is able to give good-quality results in short time.

### The Balance Constraint Family

"... Abstract. The BALANCE constraint introduced by Beldiceanu ensures solutions are balanced. This is useful when, for example, there is a requirement for solutions to be fair. BALANCE bounds the difference B between the minimum and maximum number of occurrences of the values assigned to the variables. ..."

Abstract
- Add to MetaCart

(Show Context)
Abstract. The BALANCE constraint introduced by Beldiceanu ensures solutions are balanced. This is useful when, for example, there is a requirement for solutions to be fair. BALANCE bounds the difference B between the minimum and maximum number of occurrences of the values assigned to the variables. We show that achieving domain consistency on BALANCE is NP-hard. We therefore introduce a variant, ALLBALANCE with a similar semantics that is only polynomial to propagate. We consider various forms of ALLBALANCE and focus on ATMOSTALLBALANCE which achieves what is usually the main goal, namely constraining the upper bound on B. We provide a specialized propagation algorithm, and a powerful decomposition both of which run in low polynomial time. Experimental results demonstrate the promise of these new filtering methods.