Algorithms for propositional model counting

AbstractWe present algorithms for the propositional model counting problem #SAT. The algorithms utilize tree decompositions of certain graphs associated with the given CNF formula; in particular we consider primal, dual, and incidence graphs. We describe the algorithms coherently for a direct comparison and with sufficient detail for making an actual implementation reasonably easy. We discuss several aspects of the algorithms including worst-case time and space requirements

A Backtracking-Based Algorithm for Computing Hypertree-Decompositions

Hypertree decompositions of hypergraphs are a generalization of tree decompositions of graphs. The corresponding hypertree-width is a measure for the cyclicity and therefore tractability of the encoded computation problem. Many NP-hard decision and computation problems are known to be tractable on instances whose structure corresponds to hypergraphs of bounded hypertree-width. Intuitively, the smaller the hypertree-width, the faster the computation problem can be solved. In this paper, we present the new backtracking-based algorithm det-k-decomp for computing hypertree decompositions of small width. Our benchmark evaluations have shown that det-k-decomp significantly outperforms opt-k-decomp, the only exact hypertree decomposition algorithm so far. Even compared to the best heuristic algorithm, we obtained competitive results as long as the hypergraphs are not too large.Comment: 19 pages, 6 figures, 3 table

The ABC130 barrel module prototyping programme for the ATLAS strip tracker

For the Phase-II Upgrade of the ATLAS Detector, its Inner Detector, consisting of silicon pixel, silicon strip and transition radiation sub-detectors, will be replaced with an all new 100 % silicon tracker, composed of a pixel tracker at inner radii and a strip tracker at outer radii. The future ATLAS strip tracker will include 11,000 silicon sensor modules in the central region (barrel) and 7,000 modules in the forward region (end-caps), which are foreseen to be constructed over a period of 3.5 years. The construction of each module consists of a series of assembly and quality control steps, which were engineered to be identical for all production sites. In order to develop the tooling and procedures for assembly and testing of these modules, two series of major prototyping programs were conducted: an early program using readout chips designed using a 250 nm fabrication process (ABCN-25) and a subsequent program using a follow-up chip set made using 130 nm processing (ABC130 and HCC130 chips). This second generation of readout chips was used for an extensive prototyping program that produced around 100 barrel-type modules and contributed significantly to the development of the final module layout. This paper gives an overview of the components used in ABC130 barrel modules, their assembly procedure and findings resulting from their tests.Comment: 82 pages, 66 figure

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Abstract Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries

Reasoning about specifications in model checking

Eine der praktisch erfolgreichsten formalen Verifikationstechniken ist Model Checking, ein Ansatz um logische Eigenschaften endlicher Zustandssysteme algorithmisch zu verifizieren.Auf Eingabe eines Systemmodells in Form eines endlichen Zustandsübergangsgraphen und einer in einer Temporallogik formulierten Spezifikation, stellt ein Model Checker automatisch fest, ob das Modell die Spezifikation erfüllt. In dieser Dissertation werden verschiedene Ansätze zum Analysieren von Spezifikationen im Allgemeinen und temporallogischen Spezifikationen im Speziellen untersucht. Durch derartige Methoden können zusätzliche Informationen gewonnen werden, um zu entscheiden, ob das zu untersuchende System seine Anforderungen erfüllt. Insbesondere werden die folgenden Fragen behandelt: (i) Was kann über die Zusammensetzung zweier Teilsysteme, die ihre jeweiligen Spezifikationen erfüllen, ausgesagt werden? Diese Frage ist besonders dann von Bedeutung, wenn ein zusammengesetztes System zu groß ist um als Ganzes untersucht zu werden. Der Schwerpunkt der vorliegenden Arbeit liegt bei Systemen deren Komponenten zirkulär voneinander abhängen. In diesem Kontext wird eine abstrakte zirkuläre Schnittregel und eine abstrakte zirkuläre kompositionelle Schlussregel präsentiert.(ii) Wie kann eine unvollständige temporallogische Spezifikation effizient vervollständigt werden, so dass sie von einem gegebenen Modell erfüllt wird? Derartige unvollständige Spezifikationen werden temporallogische Queries genannt. Der Schwerpunkt der vorliegenden Arbeit liegt bei Queries mit einer einzigen stärksten Lösung. Unter anderem werden syntaktische Fragmente solcher Queries und effiziente Lösungsalgorithmen präsentiert.(iii) Wenn ein gegebenes Modell seine Spezifikation erfüllt, erfolgt dies auf die intendierte Art? Die Beantwortung dieser Frage ist in der Literatur bekannt unter dem Namen Vacuity Detection. Sie ist praktisch von großer Bedeutung, da vacuous (d.h., auf triviale Weise) erfüllte Spezifikationen oft auf ein Problem im Systemdesign oder der Spezifikation hinweisen. In der vorliegenden Arbeit wird der klassische Vacuity-Begriff durch eine Parametrisierung verallgemeinert, die es ermöglicht ein Problem zu lösen, auf das von Amir Pnueli hingewiesen wurde.One of the practically most successful formal verification techniques is model checking, an approach for algorithmically verifying logical properties of finite state systems. Given a system model in the form of a finite state transition graph and a specification expressed in some temporal logic, a model checker automatically determines whether the model satisfies the specification. In this thesis, we investigate several approaches in order to reason about specifications in general and temporal logic specifications in particular. By such reasoning methods, it is possible to obtain additional information to support verification and validation engineers in their task to decide whether the system under consideration satisfies its requirements. In particular, we are interested in three main questions:(i) Given the specifications satisfied by two systems, what can we say about the system obtained by composing these systems? This question is of great importance for composed systems that are too large to be handled at once. Our focus lies in systems whose components depend on each other in a circular manner. In this context, we present an abstract circular cut and an abstract circular compositional reasoning rule.(ii) Given a system model and an incomplete temporal logic specification, how can the given specification be efficiently completed such that it is satisfied by the model? Incomplete specifications of this kind are called temporal logic queries. Our focus lies in queries with single strongest solutions. Among other things, we present syntactic fragments of such queries and efficient algorithms for solving them.(iii) Given a system model that satisfies its specifications, does the model satisfy the specification in the intended way? In the literature, deciding this question is well known under the name vacuity detection.It is of great importance in practice, since vacuously (i.e., due to a trivial reason) satisfied specifications often point to a real problem in either the system design or the specification. We generalize the classical notion of vacuity by a parameterization, which enables us to solve a problem posed by Amir Pnueli.21

Hypertree-decomposition via branch-decomposition

Hypertree-decomposition is the most general approach in the literature for identifying tractable computation problems encoded as hypergraphs. We show how the heuristic branch-decomposition approach for ordinary graphs of [Cook and Seymour, 2003] can be used for the heuristic construction of hypertree-decompositions.

Tractable Cases of the Extended Global Cardinality Constraint

We study the consistency problem for extended global cardinality (EGC) constraints. An EGC constraint consists of a set X of variables, a set D of values, a domain D(x) ⊆ D for each variable x, anda“cardinality set ” K(d) of non-negative integers for each value d. The problem is to instantiate each variable x with a value in D(x) such that for each value d, the number of variables instantiated with d belongs to the cardinality set K(d). It is known that this problem is NP-complete in general, but solvable in polynomial time if all cardinality sets are intervals. First we pinpoint connections between EGC constraints and general factors in graphs. This allows us to extend the known polynomial-time case to certain non-interval cardinality sets. Second we consider EGC constraints under restrictions in terms of the treewidth of the value graph (the bipartite graph representing variable-value pairs) and the cardinality-width (the largest integer occurring in the cardinality sets). We show that EGC constraints can be solved in polynomial time for instances of bounded treewidth, where the order of the polynomial depends on the treewidth. We show that (subject to the complexity theoretic assumption FPT � = W[1]) this dependency cannot be avoided without imposing additional restrictions. If, however, also the cardinality-width is bounded, this dependency gets removed and EGC constraints can be solved in linear time