5,912 research outputs found
Solving of constraint satisfaction problems by reduction to SAT
Mnogi realni problemi se danas mogu predstaviti u obliku problema zadovoljenja
ogranicenja (CSP) i zatim rešiti nekom od mnogobrojnih tehnika za rešavanje
ovog problema. Jedna od tehnika podrazumeva svođenje na problem SAT, tj.
problem iskazne zadovoljivosti. Promenljive i ogranicenja problema CSP se prevode
(kodiraju) u SAT instancu, ona se potom rešava pomocu modernih SAT rešavaca
i rešenje se, ako postoji, prevodi u rešenje problema CSP. Glavni cilj ove teze je
unapređenje rešavanja problema CSP svođenjem na SAT.
Razvijena su dva nova hibridna kodiranja (prevođenja u SAT formulu) koja
kombinuju dobre strane postojecih kodiranja. Dat je dokaz korektnosti jednog od
kodiranja koji do sada nije postojao u literaturi. Razvijen je sistem meSAT koji
omogucava svođenje problema CSP na SAT pomocu cetiri osnovna i dva hibridna
kodiranja, kao i rešavanje problema CSP svođenjem na dva problema srodna problemu
SAT, SMT i PB.
Razvijen je portfolio za automatski odabir kodiranja/rešavaca za ulaznu instancu
koju je potrebno rešiti i pokazano je da je razvijeni portfolio uporediv sa najefikasnijim
savremenim pristupima. Prikazan je novi pristup zasnovan na kratkim vremenskim
ogranicenjima sa ciljem da se znacajno smanji vreme pripreme portfolija.
Pokazano je da se ovim pristupom dobijaju rezultati konkurentni onima koji se dobijaju
korišcenjem standardnog vremena za pripremu. Izvršeno je poređenje nekoliko
tehnika mašinskog ucenja, sa ciljem da se ustanovi koja od njih je pogodnija za
pristup sa kratkim treniranjem.
Prikazan je jedan realan problem, problem raspoređivanja kontrolora leta, kao i
tri njegova modela. Veliki broj metoda rešavanja i raznovrsnih rešavaca je upotrebljeno
za rešavanje ovog problema. Razvijeno je više optimizacionih tehnika koje
imaju za cilj pronalaženje optimalnih rešenja problema. Pokazuje se da je najefikasnija
hibridna tehnika koja kombinuje svođenje na SAT i lokalnu pretragu.
Razmotren je i problem sudoku, kao i postojece tehnike rešavanja sudoku zagonetki
vecih dimenzija od 9 x 9. Pokazuje se da je u rešavanju ovih zagonetki
najefikasnije vec postojece svođenje na SAT. Unapređen je postojeci algoritam za
generisanje velikih sudoku zagonetki. Pokazano je da jednostavna pravila preprocesiranja
dodatno unapređuju brzinu generisanja sudokua.Many real-world problems can be modeled as constraint satisfaction
problems (CSPs) and then solved by one of many available techniques for solving
these problems. One of the techniques is reduction to SAT, i.e. Boolean Satisfiability
Problem. Variables and constraints of CSP are translated (encoded) to SAT
instance, that is then solved by state-of-the-art SAT solvers and solution, if exists,
is translated to the solution of the original CSP. The main aim of this thesis is to
improve CSP solving techniques that are using reduction to SAT.
Two new hybrid encodings of CSPs to SAT are presented and they combine good
sides of the existing encodings. We give the proof of correctness of one encoding
that did not exist in literature. We developed system meSAT that enables reduction
of CSPs to SAT by using 4 basic and 2 hybrid encodings. The system also enables
solving of CSPs by reduction to two problems related to SAT, SMT and PB.
We developed a portfolio for automated selection of encoding/solver to be used
on some new instance that needs to be solved. The developed portfolio is comparable
with the state-of-the-art portfolios. We developed a hybrid approach based on short
solving timeouts with the aim of significantly reducing the preparation time of a
portfolio. By using this approach, we got results comparable to the ones obtained
by using preparation time of usual length. We made comparison between several
machine learning techniques with the aim to find out which one is the best suited
for the short training approach.
The problem of assigning air traffic controllers to shifts is described and three
models of this problem are presented. We used a large number of different solving
methods and a diverse set of solvers for solving this problem. We developed optimization
techniques that aim to find optimal solutions of the problem. A hybrid
technique combining reduction to SAT and local search is shown to be the most
efficient one.
We also considered sudoku puzzles and the existing techniques of solving the
puzzles of greater size than 9x9. Amongst the used techniques, the existing reduction
to SAT is the most efficient in solving these puzzles. We improved the existing
algorithm for generating large sudoku puzzles. It is shown that simple preprocessing
rules additionally improve speed of generating large sudokus
An Enhanced Features Extractor for a Portfolio of Constraint Solvers
Recent research has shown that a single arbitrarily efficient solver can be
significantly outperformed by a portfolio of possibly slower on-average
solvers. The solver selection is usually done by means of (un)supervised
learning techniques which exploit features extracted from the problem
specification. In this paper we present an useful and flexible framework that
is able to extract an extensive set of features from a Constraint
(Satisfaction/Optimization) Problem defined in possibly different modeling
languages: MiniZinc, FlatZinc or XCSP. We also report some empirical results
showing that the performances that can be obtained using these features are
effective and competitive with state of the art CSP portfolio techniques
ASlib: A Benchmark Library for Algorithm Selection
The task of algorithm selection involves choosing an algorithm from a set of
algorithms on a per-instance basis in order to exploit the varying performance
of algorithms over a set of instances. The algorithm selection problem is
attracting increasing attention from researchers and practitioners in AI. Years
of fruitful applications in a number of domains have resulted in a large amount
of data, but the community lacks a standard format or repository for this data.
This situation makes it difficult to share and compare different approaches
effectively, as is done in other, more established fields. It also
unnecessarily hinders new researchers who want to work in this area. To address
this problem, we introduce a standardized format for representing algorithm
selection scenarios and a repository that contains a growing number of data
sets from the literature. Our format has been designed to be able to express a
wide variety of different scenarios. Demonstrating the breadth and power of our
platform, we describe a set of example experiments that build and evaluate
algorithm selection models through a common interface. The results display the
potential of algorithm selection to achieve significant performance
improvements across a broad range of problems and algorithms.Comment: Accepted to be published in Artificial Intelligence Journa
Proteus: A Hierarchical Portfolio of Solvers and Transformations
In recent years, portfolio approaches to solving SAT problems and CSPs have
become increasingly common. There are also a number of different encodings for
representing CSPs as SAT instances. In this paper, we leverage advances in both
SAT and CSP solving to present a novel hierarchical portfolio-based approach to
CSP solving, which we call Proteus, that does not rely purely on CSP solvers.
Instead, it may decide that it is best to encode a CSP problem instance into
SAT, selecting an appropriate encoding and a corresponding SAT solver. Our
experimental evaluation used an instance of Proteus that involved four CSP
solvers, three SAT encodings, and six SAT solvers, evaluated on the most
challenging problem instances from the CSP solver competitions, involving
global and intensional constraints. We show that significant performance
improvements can be achieved by Proteus obtained by exploiting alternative
view-points and solvers for combinatorial problem-solving.Comment: 11th International Conference on Integration of AI and OR Techniques
in Constraint Programming for Combinatorial Optimization Problems. The final
publication is available at link.springer.co
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Automated generation of computationally hard feature models using evolutionary algorithms
This is the post-print version of the final paper published in Expert Systems with Applications. The published article is available from the link below. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. Copyright @ 2014 Elsevier B.V.A feature model is a compact representation of the products of a software product line. The automated extraction of information from feature models is a thriving topic involving numerous analysis operations, techniques and tools. Performance evaluations in this domain mainly rely on the use of random feature models. However, these only provide a rough idea of the behaviour of the tools with average problems and are not sufficient to reveal their real strengths and weaknesses. In this article, we propose to model the problem of finding computationally hard feature models as an optimization problem and we solve it using a novel evolutionary algorithm for optimized feature models (ETHOM). Given a tool and an analysis operation, ETHOM generates input models of a predefined size maximizing aspects such as the execution time or the memory consumption of the tool when performing the operation over the model. This allows users and developers to know the performance of tools in pessimistic cases providing a better idea of their real power and revealing performance bugs. Experiments using ETHOM on a number of analyses and tools have successfully identified models producing much longer executions times and higher memory consumption than those obtained with random models of identical or even larger size.European Commission (FEDER), the Spanish Government and
the Andalusian Government
Fast counting with tensor networks
We introduce tensor network contraction algorithms for counting satisfying
assignments of constraint satisfaction problems (#CSPs). We represent each
arbitrary #CSP formula as a tensor network, whose full contraction yields the
number of satisfying assignments of that formula, and use graph theoretical
methods to determine favorable orders of contraction. We employ our heuristics
for the solution of #P-hard counting boolean satisfiability (#SAT) problems,
namely monotone #1-in-3SAT and #Cubic-Vertex-Cover, and find that they
outperform state-of-the-art solvers by a significant margin.Comment: v2: added results for monotone #1-in-3SAT; published versio
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