scholarly journals CNF-SAT modelling for banyan-type networks and its application for assessing the rearrangeability

2021 ◽  
Vol 2090 (1) ◽  
pp. 012133
Author(s):  
S Ohta
Keyword(s):  
Normal Form ◽  
Conjunctive Normal Form ◽  
Switching Network ◽  
Theoretical Studies ◽  
Sat Problem ◽  
Sat Solver ◽  
Theoretical Analyses

Abstract A banyan-type network is a switching network, which is constructed by placing unit switches with two inputs and two outputs in s (s > 1) stages. In each stage, 2 n – 1 (n > 1) unit switches are aligned. Past studies conjecture that this network becomes rearrangeable when s ≥ 2n-1. Although a considerable number of theoretical analyses have been done, the rearrangeability of the banyan-type network with 2n – 1 or more stages is not completely proved. As a tool to assess the rearrangeability, this study presents a CNF-SAT (conjunctive normal form - satisfiability) modelling scheme for banyan-type networks. In the proposed scheme, the routing is formulated to a SAT problem represented in CNF. By feeding the problem to a SAT solver, it is found whether the problem is satisfiable or unsatisfiable. If the problem is unsatisfiable for a certain request, the network is not rearrangeable. By contrast, if the problem is satisfiable for any requests, the network is rearrangeable. This study applies the CNF-SAT modelling scheme to various configurations of 2n – 1 stage banyan-type networks. These networks are assessed for rearrangeability by solving the SAT problems. The proposed method will be helpful to conduct future theoretical studies on banyan-type networks.

Chapter 9. Preprocessing in SAT Solving

2021 ◽  
Author(s):  
Armin Biere ◽  
Matti Järvisalo ◽  
Benjamin Kiesl
Keyword(s):  
Normal Form ◽  
Conjunctive Normal Form ◽  
Boolean Satisfiability ◽  
Sat Solving ◽  
Speed Up ◽  
Sat Solver ◽  
Main Ideas ◽  
Simplification Techniques

Preprocessing has become a key component of the Boolean satisfiability (SAT) solving workflow. In practice, preprocessing is situated between the encoding phase and the solving phase, with the aim of decreasing the total solving time by applying efficient simplification techniques on SAT instances to speed up the search subsequently performed by a SAT solver. In this chapter, we overview key preprocessing techniques proposed in the literature. While the main focus is on techniques applicable to formulas in conjunctive normal form (CNF), we also selectively cover main ideas for preprocessing structural and higher-level SAT instance representations.

scholarly journals A kommunikációs gráfok és a fekete-fehér SAT probléma közti összefüggések vizsgálata

2021 ◽  
Author(s):  
Franciska Rajna
Keyword(s):  
Wireless Sensor Networks ◽  
Sensor Networks ◽  
Normal Form ◽  
Directed Graphs ◽  
Conjunctive Normal Form ◽  
Wireless Sensor ◽  
Sat Problem ◽  
Black And White ◽  
Communication Graphs ◽  
The Relationship

Ebben a cikkben a kommunikációs gráfok és a fekete-fehér SAT probléma közötti összefüggéseket vizsgálom. A kommunikációs gráfok olyan speciális hurokélmentes irányított gráfok, amelyeknek csúcsai logikai változók, az élei pedig a kommunikációt reprezentálják. Ilyen típusú gráfokkal lehet többek között vezeték nélküli szenzorhálózatokat is modellezni. A cikkben bemutatom a fekete-fehér SAT problémát. A fekete-fehér SAT problémák olyan logikai formulák, amelyek majdnem kielégíthetetlenek, csak két megoldásuk van, az úgynevezett fehér hozzárendelés, ahol minden változó igaz, és a fekete hozzárendelés, amelyben minden változó hamis. A fekete-fehér SAT problémák ekvivalensek az olyan konjunktív normálformában lévő logikai formulákkal, amelyekben minden klózban pozitív és negatív literálok vegyesen szerepelnek (például ilyen 3SAT klózok a -++, --+), de sem a fehér klóz, amelyben minden literál pozitív, sem a fekete klóz, amelyben minden literál negatív, nem vezethető le. Továbbá ismertetem, és hatékonyság szempontjából elemzem a kommunikációs gráfok különböző logikai modelljeit (Erős modell, Balatonboglár modell, Egyszerűsített BB modell, Gyenge modell). ----- Investigation of the relationship between communication graphs and the black and white sat ----- In this article, I examine the relationships between communication graphs and the black-andwhite SAT problem. Communication graphs are special loop-free directed graphs whose vertices are logical variables and whose edges represent communication. These types of graphs can be used to model wireless sensor networks (WSNs), among other things. I present the black-and-white SAT problem. Black-and-white SAT problems are logical formulas that are almost unsatisfiable, they have only two solutions, the so-called white assignment, where all variables are true, and the black assignment, in which all variables are false. Black-and-white SAT problems are equivalent to logical formulas in a conjunctive normal form in which positive and negative literals are mixed in each clause (e.g., such 3-SAT clauses are - ++, - +), but not the white clause in which all literals are positive, nor the black clause in which all literals are negative cannot be deduced. I also describe and analyze the different logical models of communication graphs (Strong model, Balatonboglár model, Simplified BB model, Weak model) in terms of efficiency.

METHODS OF REDUCING OF LARGE BOOLEAN FORMULAS REPRESENTED IN A CONJUNCTIVE NORMAL FORM FOR DETERMINING THEIR SATISFIABILITY

2020 ◽  
Author(s):  
N.I. Gdansky ◽  
◽  
A.A. Denisov ◽  
Keyword(s):  
Normal Form ◽  
Normal Forms ◽  
Conjunctive Normal Form ◽  
Boolean Formulas

The article explores the satisfiability of conjunctive normal forms used in modeling systems.The problems of CNF preprocessing are considered.The analysis of particular methods for reducing this formulas, which have polynomial input complexity is given.

A reduction class containing formulas with one monadic predicate and one binary function symbol

1976 ◽  
Vol 41 (1) ◽  
pp. 45-49
Author(s):  
Charles E. Hughes
Keyword(s):  
Normal Form ◽  
Predicate Symbol ◽  
Conjunctive Normal Form ◽  
Function Symbol ◽  
Predicate Calculus ◽  
Binary Function ◽  
First Order ◽  
The Matrix ◽  
Reduction Class ◽  
Order Predicate Calculus

AbstractA new reduction class is presented for the satisfiability problem for well-formed formulas of the first-order predicate calculus. The members of this class are closed prenex formulas of the form ∀x∀yC. The matrix C is in conjunctive normal form and has no disjuncts with more than three literals, in fact all but one conjunct is unary. Furthermore C contains but one predicate symbol, that being unary, and one function symbol which symbol is binary.

Chapter 13. Symmetry and Satisfiability

2021 ◽  
Author(s):  
Karem A. Sakallah
Keyword(s):  
Group Theory ◽  
Normal Form ◽  
Boolean Functions ◽  
Search Algorithm ◽  
Conjunctive Normal Form ◽  
Search Space ◽  
Decision Problems ◽  
Mathematical Language ◽  
Sat Solvers ◽  
Speed Up

Symmetry is at once a familiar concept (we recognize it when we see it!) and a profoundly deep mathematical subject. At its most basic, a symmetry is some transformation of an object that leaves the object (or some aspect of the object) unchanged. For example, a square can be transformed in eight different ways that leave it looking exactly the same: the identity “do-nothing” transformation, 3 rotations, and 4 mirror images (or reflections). In the context of decision problems, the presence of symmetries in a problem’s search space can frustrate the hunt for a solution by forcing a search algorithm to fruitlessly explore symmetric subspaces that do not contain solutions. Recognizing that such symmetries exist, we can direct a search algorithm to look for solutions only in non-symmetric parts of the search space. In many cases, this can lead to significant pruning of the search space and yield solutions to problems which are otherwise intractable. This chapter explores the symmetries of Boolean functions, particularly the symmetries of their conjunctive normal form (CNF) representations. Specifically, it examines what those symmetries are, how to model them using the mathematical language of group theory, how to derive them from a CNF formula, and how to utilize them to speed up CNF SAT solvers.

NAE-resolution: A new resolution refutation technique to prove not-all-equal unsatisfiability

2020 ◽  
Vol 30 (7) ◽  
pp. 736-751
Author(s):  
Hans Kleine Büning ◽  
P. Wojciechowski ◽  
K. Subramani
Keyword(s):  
Normal Form ◽  
Conjunctive Normal Form ◽  
Principal Result ◽  
Satisfying Assignment ◽  
Boolean Formulas ◽  
Complete Procedure ◽  
Np Complete ◽  
Resolution Refutation ◽  
Original Formula ◽  
Cnf Formulas

AbstractIn this paper, we analyze Boolean formulas in conjunctive normal form (CNF) from the perspective of read-once resolution (ROR) refutation schemes. A read-once (resolution) refutation is one in which each clause is used at most once. Derived clauses can be used as many times as they are deduced. However, clauses in the original formula can only be used as part of one derivation. It is well known that ROR is not complete; that is, there exist unsatisfiable formulas for which no ROR exists. Likewise, the problem of checking if a 3CNF formula has a read-once refutation is NP-complete. This paper is concerned with a variant of satisfiability called not-all-equal satisfiability (NAE-satisfiability). A CNF formula is NAE-satisfiable if it has a satisfying assignment in which at least one literal in each clause is set to false. It is well known that the problem of checking NAE-satisfiability is NP-complete. Clearly, the class of CNF formulas which are NAE-satisfiable is a proper subset of satisfiable CNF formulas. It follows that traditional resolution cannot always find a proof of NAE-unsatisfiability. Thus, traditional resolution is not a sound procedure for checking NAE-satisfiability. In this paper, we introduce a variant of resolution called NAE-resolution which is a sound and complete procedure for checking NAE-satisfiability in CNF formulas. The focus of this paper is on a variant of NAE-resolution called read-once NAE-resolution in which each clause (input or derived) can be part of at most one NAE-resolution step. Our principal result is that read-once NAE-resolution is a sound and complete procedure for 2CNF formulas. Furthermore, we provide an algorithm to determine the smallest such NAE-resolution in polynomial time. This is in stark contrast to the corresponding problem concerning 2CNF formulas and ROR refutations. We also show that the problem of checking whether a 3CNF formula has a read-once NAE-resolution is NP-complete.

Logic on electronic computers: a practical method for reducing expressions to conjunctive normal form

1956 ◽  
Vol 52 (2) ◽  
pp. 161-173
Author(s):  
N. A. Routledge
Keyword(s):  
Normal Form ◽  
Real Number ◽  
Electronic Computer ◽  
Propositional Calculus ◽  
Practical Method ◽  
Conjunctive Normal Form ◽  
Electronic Computers ◽  
The Given

ABSTRACTIn § 1 we introduce our system and prove a theorem about its syntax. In § 2 we recall some stock results about the propositional calculus. In § 3 we consider a method of deriving an expression from a given expression and a real number. In § 4 we use this to derive a sequence of expressions from a given expression. In § 5 this sequence is shown to be just all the terms of a conjunctive normal form of the given expression. In § 6 we note that we may not need to produce all of these terms. In § 7 we describe a practical method (suitable for a binary digital electronic computer) which results from all this, and in § 8 we attempt to explain just why this is so.

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