174,036 research outputs found
From Causes for Database Queries to Repairs and Model-Based Diagnosis and Back
In this work we establish and investigate connections between causes for
query answers in databases, database repairs wrt. denial constraints, and
consistency-based diagnosis. The first two are relatively new research areas in
databases, and the third one is an established subject in knowledge
representation. We show how to obtain database repairs from causes, and the
other way around. Causality problems are formulated as diagnosis problems, and
the diagnoses provide causes and their responsibilities. The vast body of
research on database repairs can be applied to the newer problems of computing
actual causes for query answers and their responsibilities. These connections,
which are interesting per se, allow us, after a transition -inspired by
consistency-based diagnosis- to computational problems on hitting sets and
vertex covers in hypergraphs, to obtain several new algorithmic and complexity
results for database causality.Comment: To appear in Theory of Computing Systems. By invitation to special
issue with extended papers from ICDT 2015 (paper arXiv:1412.4311
Combinatorial Hopf algebras in quantum field theory I
This manuscript stands at the interface between combinatorial Hopf algebra
theory and renormalization theory. Its plan is as follows: Section 1 is the
introduction, and contains as well an elementary invitation to the subject. The
rest of part I, comprising Sections 2-6, is devoted to the basics of Hopf
algebra theory and examples, in ascending level of complexity. Part II turns
around the all-important Faa di Bruno Hopf algebra. Section 7 contains a first,
direct approach to it. Section 8 gives applications of the Faa di Bruno algebra
to quantum field theory and Lagrange reversion. Section 9 rederives the related
Connes-Moscovici algebras. In Part III we turn to the Connes-Kreimer Hopf
algebras of Feynman graphs and, more generally, to incidence bialgebras. In
Section10 we describe the first. Then in Section11 we give a simple derivation
of (the properly combinatorial part of) Zimmermann's cancellation-free method,
in its original diagrammatic form. In Section 12 general incidence algebras are
introduced, and the Faa di Bruno bialgebras are described as incidence
bialgebras. In Section 13, deeper lore on Rota's incidence algebras allows us
to reinterpret Connes-Kreimer algebras in terms of distributive lattices. Next,
the general algebraic-combinatorial proof of the cancellation-free formula for
antipodes is ascertained; this is the heart of the paper. The structure results
for commutative Hopf algebras are found in Sections 14 and 15. An outlook
section very briefly reviews the coalgebraic aspects of quantization and the
Rota-Baxter map in renormalization.Comment: 94 pages, LaTeX figures, precisions made, typos corrected, more
references adde
Learning participation as systems practice
We describe an evolving praxeology for Systems Practice for managing complexity built on 30 years of developing supported open learning opportunities in the area of Systems within the curriculum of The Open University (UK). We ground this description in two specific examples of how notions of participation are incorporated conceptually and practically into a learners programme of study by considering: (i) the postgraduate course 'Environmental Decision Making. A Systems Approach' (T860) and (ii) the undergraduate course 'Managing complexity. A systems approach' (T306)
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Some reflections on a knowledge transfer strategy: a systemic inquiry
This paper presents a case study of a systemic inquiry into a knowledge transfer strategy (KTS) by a division of a UK Ministry. Two main points are made. Firstly that it is possible to 'build' a generalisable form of practice as a response to experiences of complexity by initiating a systemic inquiry that fosters the emergence of a learning system. Secondly, that exploring how metaphors reveal and conceal offers scope for shifting the 'mental furniture' of participants as part of a systemic inquiry.
This inquiry proceeded with a process designed for the circumstances - there are no blue-prints. A key design aspiration was that those participating might experience a coherence between espoused theory and theory in use in relation to considering the KTS as if it were a second-order learning system. In this aim it succeeded. The inquiry suggested two sets of considerations for the design of learning systems and a potentially fruitful line of further inquiry
Stable Invitations
We consider the situation in which an organizer is trying to convene an
event, and needs to choose a subset of agents to be invited. Agents have
preferences over how many attendees should be at the event and possibly also
who the attendees should be. This induces a stability requirement: All invited
agents should prefer attending to not attending, and all the other agents
should not regret being not invited. The organizer's objective is to find the
invitation of maximum size subject to the stability requirement. We investigate
the computational complexity of finding the maximum stable invitation when all
agents are truthful, as well as the mechanism design problem when agents may
strategically misreport their preferences.Comment: To appear in COMSOC 201
Paradox as invitation to act in problematic change situations
It has been argued that organizational life typically contains paradoxical situations such as efforts to manage change which nonetheless seem to reinforce inertia. Four logical options for coping with paradox have been explicated, three of which seek resolution and one of which âkeeps the paradox openâ. The purpose of this article is to explore the potential for managerial action where the paradox is held open through the use of theory on âserious playfulnessâ. Our argument is that paradoxes, as intrinsic features in organizational life, cannot always be resolved through cognitive processes. What may be possible, however, is that such paradoxes are transformed, or âmoved onâ through action and as a result the overall change effort need not be stalled by the existence of embedded paradoxes
Building an adiabatic quantum computer simulation in the classroom
We present a didactic introduction to adiabatic quantum computation (AQC) via the explicit construction of a classical simulator of quantum computers. This constitutes a suitable route to introduce several important concepts for advanced undergraduates in physics: quantum many-body systems, quantum phase transitions, disordered systems, spin-glasses, and computational complexity theory. (C) 2018 American Association of Physics Teachers.The authors want to acknowledge the faculty and students of the Facultad de InformĂĄtica of UCM (Madrid) for their kind invitation to deliver this crash course, particularly to I. RodrĂguez-Laguna and N. MartĂ. The authors would also like to thank G. Sierra for very useful comments on the manuscript. This work was funded by the Spanish government through Grant Nos. FIS2015-69167-C2-1-P and FIS2015-66020-C2-1-
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