5,706 research outputs found
Postcondition-preserving fusion of postorder tree transformations
Tree transformations are commonly used in applications such as program rewriting in compilers. Using a series of simple transformations to build a more complex system can make the resulting software easier to understand, maintain, and reason about. Fusion strategies for combining such successive tree transformations promote this modularity, whilst mitigating the performance impact from increased numbers of tree traversals. However, it is important to ensure that fused transformations still perform their intended tasks. Existing approaches to fusing tree transformations tend to take an informal approach to soundness, or be too restrictive to consider the kind of transformations needed in a compiler. We use postconditions to define a more useful formal notion of successful fusion, namely postcondition-preserving fusion. We also present criteria that are sufficient to ensure postcondition-preservation and facilitate modular reasoning about the success of fusion
Space-time S-matrix and Flux-tube S-matrix IV. Gluons and Fusion
We analyze the pentagon transitions involving arbitrarily many flux-tube
gluonic excitations and bound states thereof in planar N=4 Super-Yang-Mills
theory. We derive all-loop expressions for all these transitions by
factorization and fusion of the elementary transitions for the lightest gluonic
excitations conjectured in a previous paper. We apply the proposals so obtained
to the computation of MHV and NMHV scattering amplitudes at any loop order and
find perfect agreement with available perturbative data up to four loops.Comment: 26+14 page
Kinetic equations for Stark line shapes
The BBGKY formalism is revisited in the framework of plasma spectroscopy. We
address the issue of Stark line shape modeling by using kinetic transport
equations. In the most simplified treatment of these equations, triple
correlations between an emitter and the perturbing charged particles are
neglected and a collisional description of Stark effect is obtained. Here we
relax this assumption and retain triple correlations using a generalization of
the Kirkwood truncature hypothesis to quantum operator. An application to
hydrogen lines is done in the context of plasma diagnostic, and indicates that
the neglect of triple correlations can lead to a significant overestimate of
the line width.Comment: 13 pages, 1 figur
Multiple intermediate structure deforestation by shortcut fusion
Shortcut fusion is a well-known optimization technique for functional programs. Its aim is to transform multi-pass algorithms into single pass ones, achieving deforestation of the intermediate structures that multi-pass algorithms need to construct. Shortcut fusion has already been extended in several ways. It can be applied to monadic programs, maintaining the global effects, and also to obtain circular and higher-order programs. The techniques proposed so far, however, only consider programs defined as the composition of a single producer with a single consumer. In this paper, we analyse shortcut fusion laws to deal with programs consisting of an arbitrary number of function compositions. (C) 2016 Elsevier B.V. All rights reserved.We would like to thank the anonymous reviewers for their detailed and helpful comments. This work was partially funded by ERDF - European Regional Development Fund through the COMPETE Programme (operational programme for competitiveness) and by National Funds through the FCT - Fundacao para a Ciencia e a Tecnologia (Portuguese Foundation for Science and Technology) within projects FCOMP-01-0124-FEDER-020532 and FCOMP-01-0124-FEDER-022701
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