673 research outputs found
Propagators and Violation Functions for Geometric and Workload Constraints Arising in Airspace Sectorisation
Airspace sectorisation provides a partition of a given airspace into sectors,
subject to geometric constraints and workload constraints, so that some cost
metric is minimised. We make a study of the constraints that arise in airspace
sectorisation. For each constraint, we give an analysis of what algorithms and
properties are required under systematic search and stochastic local search
Constraint Propagation and Explanation over Novel Types by Abstract Compilation
© Graeme Gange and Peter J. Stuckey. The appeal of constraint programming (CP) lies in compositionality - the ability to mix and match constraints as needed. However, this flexibility typically does not extend to the types of variables. Solvers usually support only a small set of pre-defined variable types, and extending this is not typically a simple exercise: not only must the solver engine be updated, but then the library of supported constraints must be re-implemented to support the new type. In this paper, we attempt to ease this second step. We describe a system for automatically deriving a native-code implementation of a global constraint (over novel variable types) from a declarative specification, complete with the ability to explain its propagation, a requirement if we want to make use of modern lazy clause generation CP solvers. We demonstrate this approach by adding support for wrapped-integer variables to chuffed, a lazy clause generation CP solver
Status and Future Perspectives for Lattice Gauge Theory Calculations to the Exascale and Beyond
In this and a set of companion whitepapers, the USQCD Collaboration lays out
a program of science and computing for lattice gauge theory. These whitepapers
describe how calculation using lattice QCD (and other gauge theories) can aid
the interpretation of ongoing and upcoming experiments in particle and nuclear
physics, as well as inspire new ones.Comment: 44 pages. 1 of USQCD whitepapers
Flexible constrained sampling with guarantees for pattern mining
Pattern sampling has been proposed as a potential solution to the infamous
pattern explosion. Instead of enumerating all patterns that satisfy the
constraints, individual patterns are sampled proportional to a given quality
measure. Several sampling algorithms have been proposed, but each of them has
its limitations when it comes to 1) flexibility in terms of quality measures
and constraints that can be used, and/or 2) guarantees with respect to sampling
accuracy. We therefore present Flexics, the first flexible pattern sampler that
supports a broad class of quality measures and constraints, while providing
strong guarantees regarding sampling accuracy. To achieve this, we leverage the
perspective on pattern mining as a constraint satisfaction problem and build
upon the latest advances in sampling solutions in SAT as well as existing
pattern mining algorithms. Furthermore, the proposed algorithm is applicable to
a variety of pattern languages, which allows us to introduce and tackle the
novel task of sampling sets of patterns. We introduce and empirically evaluate
two variants of Flexics: 1) a generic variant that addresses the well-known
itemset sampling task and the novel pattern set sampling task as well as a wide
range of expressive constraints within these tasks, and 2) a specialized
variant that exploits existing frequent itemset techniques to achieve
substantial speed-ups. Experiments show that Flexics is both accurate and
efficient, making it a useful tool for pattern-based data exploration.Comment: Accepted for publication in Data Mining & Knowledge Discovery journal
(ECML/PKDD 2017 journal track
The Gribov problem and QCD dynamics
In 1967, Faddeev and Popov were able to quantize the Yang-Mills theory by
introducing new particles called ghost through the introduction of a gauge.
Ever since, this quantization has become a standard textbook item. Some years
later, Gribov discovered that the gauge fixing was not complete, gauge copies
called Gribov copies were still present and could affect the infrared region of
quantities like the gauge dependent gluon and ghost propagator. This feature
was often in literature related to confinement. Some years later, the
semi-classical approach of Gribov was generalized to all orders and the
so-called GZ action was born. Ever since, many related articles were published.
This review tends to give a pedagogic review of the ideas of Gribov and the
subsequent construction of the GZ action, including many other toipics related
to the Gribov region. It is shown how the GZ action can be viewed as a
non-perturbative tool which has relations with other approaches towards
confinement. Many different features related to the GZ action shall be
discussed in detail, such as BRST breaking, the KO criterion, the propagators,
etc. We shall also compare with the lattice data and other non-perturbative
approaches, including stochastic quantization.Comment: 121 pages, 12 figures, Review article, references adde
Modern techniques for constraint solving the CASPER experience
Dissertação apresentada para obtenção do
Grau de Doutor em Engenharia Informática,
pela Universidade Nova de Lisboa, Faculdade
de Ciências e TecnologiaConstraint programming is a well known paradigm for addressing combinatorial problems which has enjoyed considerable success for solving many relevant industrial and academic problems. At the heart of constraint programming lies the constraint solver, a computer program which attempts to find a solution to the problem, i.e. an assignment of all the variables in the problemsuch that all the constraints are satisfied.
This dissertation describes a set of techniques to be used in the implementation of a constraint solver. These techniques aim at making a constraint solver more extensible and efficient,two properties which are hard to integrate in general, and in particular within a constraint solver. Specifically, this dissertation addresses two major problems: generic incremental
propagation and propagation of arbitrary decomposable constraints. For both problemswe
present a set of techniques which are novel, correct, and directly concerned with extensibility and efficiency.
All the material in this dissertation emerged from our work in designing and implementing a generic constraint solver. The CASPER (Constraint Solving Platformfor Engineering and Research)solver does not only act as a proof-of-concept for the presented techniques, but also served as the common test platform for the many discussed theoretical models. Besides the work related to the design and implementation of a constraint solver, this dissertation also
presents the first successful application of the resulting platform for addressing an open research problem, namely finding good heuristics for efficiently directing search towards a solution
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