2,745 research outputs found
Flow-Based Propagators for the SEQUENCE and Related Global Constraints
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 time down a branch of the
search tree. This improves upon the best existing domain consistency algorithm
by a factor of . The flows used in these algorithms are derived from
a linear program. Some of them differ from the flows used to propagate global
constraints like GCC since the domains of the variables are encoded as costs on
the edges rather than capacities. Such flows are efficient for maintaining
bounds consistency over large domains and may be useful for other global
constraints.Comment: Principles and Practice of Constraint Programming, 14th International
Conference, CP 2008, Sydney, Australia, September 14-18, 2008. Proceeding
Quantum Control Landscapes
Numerous lines of experimental, numerical and analytical evidence indicate
that it is surprisingly easy to locate optimal controls steering quantum
dynamical systems to desired objectives. This has enabled the control of
complex quantum systems despite the expense of solving the Schrodinger equation
in simulations and the complicating effects of environmental decoherence in the
laboratory. Recent work indicates that this simplicity originates in universal
properties of the solution sets to quantum control problems that are
fundamentally different from their classical counterparts. Here, we review
studies that aim to systematically characterize these properties, enabling the
classification of quantum control mechanisms and the design of globally
efficient quantum control algorithms.Comment: 45 pages, 15 figures; International Reviews in Physical Chemistry,
Vol. 26, Iss. 4, pp. 671-735 (2007
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
Decompositions of Grammar Constraints
A wide range of constraints can be compactly specified using automata or
formal languages. In a sequence of recent papers, we have shown that an
effective means to reason with such specifications is to decompose them into
primitive constraints. We can then, for instance, use state of the art SAT
solvers and profit from their advanced features like fast unit propagation,
clause learning, and conflict-based search heuristics. This approach holds
promise for solving combinatorial problems in scheduling, rostering, and
configuration, as well as problems in more diverse areas like bioinformatics,
software testing and natural language processing. In addition, decomposition
may be an effective method to propagate other global constraints.Comment: Proceedings of the Twenty-Third AAAI Conference on Artificial
Intelligenc
Quantum Time
We give a consistent quantum description of time, based on Page and Wootters'
conditional probabilities mechanism, that overcomes the criticisms that were
raised against similar previous proposals. In particular we show how the model
allows to reproduce the correct statistics of sequential measurements performed
on a system at different times.Comment: Final version accepted for publication on Phys. Rev.
Rigorous proof of Luttinger liquid behavior in the 1d Hubbard model
We give the first rigorous (non perturbative) proof of Luttinger liquid
behavior in the one dimensional Hubbard model, for small repulsive interaction
and values of the density different from half filling. The analysis is based on
the combination of multiscale analysis with Ward identities bases on a hidden
and approximate local chiral gauge invariance. No use is done of exact
solutions or special integrability properties of the Hubbard model, and the
results can be in fact easily generalized to include non local interactions,
magnetic fields or interaction with external potential
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