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Abstract. We propose new filtering algorithms for the SEQUENCE constraint and some extensions of the SEQUENCE constraint based on network flows. We enforce domain consistency on the SEQUENCE constraint in O(n) time down a branch of the search tree. This improves upon the best existing domain consistency algorithm by a factor of O(log n). The flows used in… (More)

- Nina Narodytska, Fahiem Bacchus
- AAAI
- 2014

Core-guided approaches to solving MAXSAT have proved to be effective on industrial problems. These approaches solve a MAXSAT formula by building a sequence of SAT formulas, where in each formula a greater weight of soft clauses can be relaxed. The soft clauses are relaxed via the addition of blocking variables, and the total weight of soft clauses that can… (More)

The SEQUENCE constraint is useful in modelling car sequencing, rostering, scheduling and related problems. We introduce half a dozen new encodings of the SEQUENCE constraint, some of which do not hinder propagation. We prove that, down a branch of a search tree, domain consistency can be enforced on the SEQUENCE constraint in just O(n log n) time. This… (More)

- Jessica Davies, George Katsirelos, Nina Narodytska, Toby Walsh
- AAAI
- 2011

We prove that it is NP-hard for a coalition of two manipulators to compute how to manipulate the Borda voting rule. This resolves one of the last open problems in the computational complexity of manipulating common voting rules. Because of this NP-hardness, we treat computing a manipulation as an approximation problem where we try to minimize the number of… (More)

- Christian Bessiere, George Katsirelos, Nina Narodytska, Toby Walsh
- IJCAI
- 2009

We show that tools from circuit complexity can be used to study decompositions of global constraints. In particular, we study decompositions of global constraints into conjunctive normal form with the property that unit propagation on the decomposition enforces the same level of consistency as a specialized propagation algorithm. We prove that a constraint… (More)

- Nina Narodytska, Toby Walsh
- ECAI
- 2014

In many real world elections, agents are not required to rank all candidates. We study three of the most common methods used to modify voting rules to deal with such partial votes. These methods modify scoring rules (like the Borda count), elimination style rules (like single transferable vote) and rules based on the tournament graph (like Copeland)… (More)

The probabilistic serial (PS) rule is a prominent randomized rule for assigning indivisible goods to agents. Although it is well known for its good fairness and welfare properties, it is not strategyproof. In view of this, we address several fundamental questions regarding equilibria under PS. Firstly, we show that Nash deviations under the PS rule can… (More)

We show that some common and important global constraints like ALL-DIFFERENT and GCC can be decomposed into simple arithmetic constraints on which we achieve bound or range consistency, and in some cases even greater pruning. These decompositions can be easily added to new solvers. They also provide other constraints with access to the state of the… (More)

- Nina Narodytska, Toby Walsh
- IJCAI
- 2007

To facilitate interactive design, the solutions to configuration problems can be compiled into a decision diagram. We develop three heuristics for reducing the time and space required to do this. These heuristics are based on the distinctive clustered and hierarchical structure of the constraint graphs of configuration problems. The first heuristic attempts… (More)

- George Katsirelos, Nina Narodytska, Toby Walsh
- CPAIOR
- 2009

An attractive mechanism to specify global constraints in rostering and other domains is via formal languages. For instance, the REGULAR and GRAMMAR constraints specify constraints in terms of the languages accepted by an automaton and a context-free grammar respectively. Taking advantage of the fixed length of the constraint, we give an algorithm to… (More)