180,856 research outputs found
Building and Refining Abstract Planning Cases by Change of Representation Language
ion is one of the most promising approaches to improve the performance of
problem solvers. In several domains abstraction by dropping sentences of a
domain description -- as used in most hierarchical planners -- has proven
useful. In this paper we present examples which illustrate significant
drawbacks of abstraction by dropping sentences. To overcome these drawbacks, we
propose a more general view of abstraction involving the change of
representation language. We have developed a new abstraction methodology and a
related sound and complete learning algorithm that allows the complete change
of representation language of planning cases from concrete to abstract.
However, to achieve a powerful change of the representation language, the
abstract language itself as well as rules which describe admissible ways of
abstracting states must be provided in the domain model. This new abstraction
approach is the core of Paris (Plan Abstraction and Refinement in an Integrated
System), a system in which abstract planning cases are automatically learned
from given concrete cases. An empirical study in the domain of process planning
in mechanical engineering shows significant advantages of the proposed
reasoning from abstract cases over classical hierarchical planning.Comment: See http://www.jair.org/ for an online appendix and other files
accompanying this articl
BeSpaceD: Towards a Tool Framework and Methodology for the Specification and Verification of Spatial Behavior of Distributed Software Component Systems
In this report, we present work towards a framework for modeling and checking
behavior of spatially distributed component systems. Design goals of our
framework are the ability to model spatial behavior in a component oriented,
simple and intuitive way, the possibility to automatically analyse and verify
systems and integration possibilities with other modeling and verification
tools. We present examples and the verification steps necessary to prove
properties such as range coverage or the absence of collisions between
components and technical details
Conceptual modelling: Towards detecting modelling errors in engineering applications
Rapid advancements of modern technologies put high demands on mathematical modelling of engineering systems. Typically, systems are no longer “simple” objects, but rather coupled systems involving multiphysics phenomena, the modelling of which involves coupling of models that describe different phenomena. After constructing a mathematical model, it is essential to analyse the correctness of the coupled models and to detect modelling errors compromising the final modelling result. Broadly, there are two classes of modelling errors: (a) errors related to abstract modelling, eg, conceptual errors concerning the coherence of a model as a whole and (b) errors related to concrete modelling or instance modelling, eg, questions of approximation quality and implementation. Instance modelling errors, on the one hand, are relatively well understood. Abstract modelling errors, on the other, are not appropriately addressed by modern modelling methodologies. The aim of this paper is to initiate a discussion on abstract approaches and their usability for mathematical modelling of engineering systems with the goal of making it possible to catch conceptual modelling errors early and automatically by computer assistant tools. To that end, we argue that it is necessary to identify and employ suitable mathematical abstractions to capture an accurate conceptual description of the process of modelling engineering systems
Size-Change Termination, Monotonicity Constraints and Ranking Functions
Size-Change Termination (SCT) is a method of proving program termination
based on the impossibility of infinite descent. To this end we may use a
program abstraction in which transitions are described by monotonicity
constraints over (abstract) variables. When only constraints of the form x>y'
and x>=y' are allowed, we have size-change graphs. Both theory and practice are
now more evolved in this restricted framework then in the general framework of
monotonicity constraints. This paper shows that it is possible to extend and
adapt some theory from the domain of size-change graphs to the general case,
thus complementing previous work on monotonicity constraints. In particular, we
present precise decision procedures for termination; and we provide a procedure
to construct explicit global ranking functions from monotonicity constraints in
singly-exponential time, which is better than what has been published so far
even for size-change graphs.Comment: revised version of September 2
Looking at Mean-Payoff through Foggy Windows
Mean-payoff games (MPGs) are infinite duration two-player zero-sum games
played on weighted graphs. Under the hypothesis of perfect information, they
admit memoryless optimal strategies for both players and can be solved in
NP-intersect-coNP. MPGs are suitable quantitative models for open reactive
systems. However, in this context the assumption of perfect information is not
always realistic. For the partial-observation case, the problem that asks if
the first player has an observation-based winning strategy that enforces a
given threshold on the mean-payoff, is undecidable. In this paper, we study the
window mean-payoff objectives that were introduced recently as an alternative
to the classical mean-payoff objectives. We show that, in sharp contrast to the
classical mean-payoff objectives, some of the window mean-payoff objectives are
decidable in games with partial-observation
Algebraic Quantum Theory on Manifolds: A Haag-Kastler Setting for Quantum Geometry
Motivated by the invariance of current representations of quantum gravity
under diffeomorphisms much more general than isometries, the Haag-Kastler
setting is extended to manifolds without metric background structure. First,
the causal structure on a differentiable manifold M of arbitrary dimension
(d+1>2) can be defined in purely topological terms, via cones (C-causality).
Then, the general structure of a net of C*-algebras on a manifold M and its
causal properties required for an algebraic quantum field theory can be
described as an extension of the Haag-Kastler axiomatic framework.
An important application is given with quantum geometry on a spatial slice
within the causally exterior region of a topological horizon H, resulting in a
net of Weyl algebras for states with an infinite number of intersection points
of edges and transversal (d-1)-faces within any neighbourhood of the spatial
boundary S^2.Comment: 15 pages, Latex; v2: several corrections, in particular in def. 1 and
in sec.
Electromagnetic Potential in Pre-Metric Electrodynamics: Causal Structure, Propagators and Quantization
An axiomatic approach to electrodynamics reveals that Maxwell electrodynamics
is just one instance of a variety of theories for which the name
electrodynamics is justified. They all have in common that their fundamental
input are Maxwell's equations (or ) and
and a constitutive law H = # F which relates the field
strength two-form and the excitation two-form . A local and linear
constitutive law defines what is called local and linear pre-metric
electrodynamics whose best known application are the effective description of
electrodynamics inside media including, e.g., birefringence. We analyze the
classical theory of the electromagnetic potential before we use methods
familiar from mathematical quantum field theory in curved spacetimes to
quantize it in a locally covariant way. Our analysis of the classical theory
contains the derivation of retarded and advanced propagators, the analysis of
the causal structure on the basis of the constitutive law (instead of a metric)
and a discussion of the classical phase space. This classical analysis sets the
stage for the construction of the quantum field algebra and quantum states.
Here one sees, among other things, that a microlocal spectrum condition can be
formulated in this more general setting.Comment: 34 pages, references added, update to published version, title
updated to published versio
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