151 research outputs found
Efficient Operations On MDDs For Building Constraint Programming Models
International audienceWe propose improved algorithms for defining the most common operations on Multi-Valued Decision Diagrams (MDDs): creation, reduction, complement , intersection, union, difference, symmetric difference, complement of union and complement of intersection. Then, we show that with these algorithms and thanks to the recent development of an efficient algorithm establishing arc consistency for MDD based constraints (MDD4R), we can simply solve some problems by modeling them as a set of operations between MDDs. We apply our approach to the regular constraint and obtain competitive results with dedicated algorithms. We also experiment our technique on a large scale problem: the phrase generation problem and we show that our approach gives equivalent results to those of a specific algorithm computing a complex automaton
Constraints First: A New MDD-based Model to Generate Sentences Under Constraints
This paper introduces a new approach to generating strongly constrained
texts. We consider standardized sentence generation for the typical application
of vision screening. To solve this problem, we formalize it as a discrete
combinatorial optimization problem and utilize multivalued decision diagrams
(MDD), a well-known data structure to deal with constraints. In our context,
one key strength of MDD is to compute an exhaustive set of solutions without
performing any search. Once the sentences are obtained, we apply a language
model (GPT-2) to keep the best ones. We detail this for English and also for
French where the agreement and conjugation rules are known to be more complex.
Finally, with the help of GPT-2, we get hundreds of bona-fide candidate
sentences. When compared with the few dozen sentences usually available in the
well-known vision screening test (MNREAD), this brings a major breakthrough in
the field of standardized sentence generation. Also, as it can be easily
adapted for other languages, it has the potential to make the MNREAD test even
more valuable and usable. More generally, this paper highlights MDD as a
convincing alternative for constrained text generation, especially when the
constraints are hard to satisfy, but also for many other prospects.Comment: To be published in Proceedings of the Thirty-Second International
Joint Conference on Artificial Intelligence, IJCAI 202
A Branch-and-Price Algorithm Enhanced by Decision Diagrams for the Kidney Exchange Problem
Kidney paired donation programs allow patients registered with an
incompatible donor to receive a suitable kidney from another donor, as long as
the latter's co-registered patient, if any, also receives a kidney from a
different donor. The kidney exchange problem (KEP) aims to find an optimal
collection of kidney exchanges taking the form of cycles and chains. Existing
exact solution methods for KEP either are designed for the case where only
cyclic exchanges are considered, or can handle long chains but are scalable as
long as cycles are short. We develop the first decomposition method that is
able to deal with long cycles and long chains for large realistic instances.
More specifically, we propose a branch-and-price framework, in which the
pricing problems are solved (for the first time in packing problems in a
digraph) through multi-valued decision diagrams. Also, we present a new upper
bound on the optimal value of KEP, stronger than the one proposed in the
literature, which is obtained via our master problem. Computational experiments
show superior performance of our method over the state of the art by optimally
solving almost all instances in the PrefLib library for multiple cycle and
chain lengths
A Decision Diagram Operation for Reachability
Saturation is considered the state-of-the-art method for computing fixpoints
with decision diagrams. We present a relatively simple decision diagram
operation called REACH that also computes fixpoints. In contrast to saturation,
it does not require a partitioning of the transition relation. We give
sequential algorithms implementing the new operation for both binary and
multi-valued decision diagrams, and moreover provide parallel counterparts. We
implement these algorithms and experimentally compare their performance against
saturation on 692 model checking benchmarks in different languages. The results
show that the REACH operation often outperforms saturation, especially on
transition relations with low locality. In a comparison between parallelized
versions of REACH and saturation we find that REACH obtains comparable speedups
up to 16 cores, although falls behind saturation at 64 cores. Finally, in a
comparison with the state-of-the-art model checking tool ITS-tools we find that
REACH outperforms ITS-tools on 29% of models, suggesting that REACH can be
useful as a complementary method in an ensemble tool
Emergence through conflict : the Multi-Disciplinary Design System (MDDS)
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Architecture, 2009.Includes bibliographical references (p. 413-430).This dissertation proposes a framework and a group of systematic methodologies to construct a computational Multi-Disciplinary Design System (MDDS) that can support the design of complex systems within a variety of domains. The way in which the resulting design system is constructed, and the capabilities it brings to bare, are totally different from the methods used in traditional sequential design. The MDDS embraces diverse areas of research that include design science, systems theory, artificial intelligence, design synthesis and generative algorithms, mathematical modeling and disciplinary analyses, optimization theory, data management and model integration, and experimental design among many others. There are five phases to generate the MDDS. These phases involve decomposition, formulation, modeling, integration, and exploration. These phases are not carried out in a sequential manner, but rather in a continuous move back and forth between the different phases. The process of building the MDDS begins with a top-down decomposition of a design concept. The design, seen as an object, is decomposed into its components and aspects, while the design, seen as a process, is decomposed into developmental levels and design activities. Then based on the process decomposition, the architecture of the MDDS is formulated into hierarchical levels each of which comprises a group of design cycles that include design modules at different degrees of abstraction. Based on the design object decomposition, the design activities which include synthesis, analysis, evaluation and optimization are modeled within the design modules.(cont.) Subsequently through a bottom-up approach, the design modules are integrated into a data flow network. This network forms MDDS as an integrated system that acts as a holistic structured functional unit that explores the design space in search of satisfactory solutions. The MDDS emergent properties are not detectable through the properties and behaviors of its parts, and can only be enucleated through a holistic approach. The MDDS is an adaptable system that is continuously dependent on, and responsive to, the uncertainties of the design process. The evolving MDDS is thus characterized a multi-level, multi-module, multi-variable and multi-resolution system. Although the MDDS framework is intended to be domain-independent, several MDDS prototypes were developed within this dissertation to generate exploratory building designs.by Anas Alfaris.Ph.D
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