903,571 research outputs found

    Building and Refining Abstract Planning Cases by Change of Representation Language

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    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

    On the solution of Lambert’s problem by regularization

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    Lambert’s problem is the two-point boundary-value problem resulting from a two-body orbital transfer between two position vectors in a given time. It lies at the very heart of several fundamental astrodynamics and space engineering problems and, as such, it has attracted the interest of scientists over centuries. In this work, we revisit the solution of Lambert’s problem based on Levi-Civita regularization developed by Carles Simó in 1973. We offer an exhaustive derivation of the theory, including proofs of all the results and the formulae employed, and we extend the algorithm to deal with multi-revolution transfers. Then, after investigating a range of initial guess search techniques and testing different numerical methods to approximate the solution, we propose a procedure in which the initial guess is assigned very efficiently by querying a pre-defined interpolating table. Then, in order to achieve both speed and robustness, we combine Newton-Raphson with safety checks to avoid out of boundary deviations to approximate the solution. We validate the method through several tests and applications, and we assess its convergence and performance. The algorithm presents no singularities, converges in all realistic scenarios and its computational cost is comparable with state of the art algorithms

    Deconstructing ‘Troops for Influence’: A First Attempt at Revealing the Anatomy of the Acclaimed ‘Troops for Influence’- Assumption

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    Having notoriously escaped the operation table to be cut open for a full intestine check-up, the anatomy of the acclaimed ‘troops for influence’- assumption finally faces a full body search. Although appearing to be somewhat of a tacitly accepted ‘truth’ both in the academic and political world, there is confusion as to how we might actually understand the assumption of ‘troops for influence’ and what it entails, as no one seems to have a clear image of how to address it. So how can we understand the assumption of ‘troops for influence’? The aim of the thesis is to develop preliminary conceptual building-blocks and a tentative analytical model as a basis for the future development of a ‘troops for influence’-theory. Through a building-block procedure, the assumption will be deconstructed and possible ways to understand and define its various components: ‘troops’ and ‘influence’ sought. Thereinafter, attention will be brought to understanding why one could expect the assumption to be valid in the first place, as well as how such a relationship might unfold in practice. As such, this thesis will constitute a pure theoretical contribution to the subject in question, illustrating the assumption by Norway’s experience in Operation EUNAVFOR Atalanta
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