3,460 research outputs found
Faithful (meta-)encodings of programmable strategies into term rewriting systems
Rewriting is a formalism widely used in computer science and mathematical
logic. When using rewriting as a programming or modeling paradigm, the rewrite
rules describe the transformations one wants to operate and rewriting
strategies are used to con- trol their application. The operational semantics
of these strategies are generally accepted and approaches for analyzing the
termination of specific strategies have been studied. We propose in this paper
a generic encoding of classic control and traversal strategies used in rewrite
based languages such as Maude, Stratego and Tom into a plain term rewriting
system. The encoding is proven sound and complete and, as a direct consequence,
estab- lished termination methods used for term rewriting systems can be
applied to analyze the termination of strategy controlled term rewriting
systems. We show that the encoding of strategies into term rewriting systems
can be easily adapted to handle many-sorted signa- tures and we use a
meta-level representation of terms to reduce the size of the encodings. The
corresponding implementation in Tom generates term rewriting systems compatible
with the syntax of termination tools such as AProVE and TTT2, tools which
turned out to be very effective in (dis)proving the termination of the
generated term rewriting systems. The approach can also be seen as a generic
strategy compiler which can be integrated into languages providing pattern
matching primitives; experiments in Tom show that applying our encoding leads
to performances comparable to the native Tom strategies
A Type System for Tom
Extending a given language with new dedicated features is a general and quite
used approach to make the programming language more adapted to problems. Being
closer to the application, this leads to less programming flaws and easier
maintenance. But of course one would still like to perform program analysis on
these kinds of extended languages, in particular type checking and inference.
In this case one has to make the typing of the extended features compatible
with the ones in the starting language.
The Tom programming language is a typical example of such a situation as it
consists of an extension of Java that adds pattern matching, more particularly
associative pattern matching, and reduction strategies.
This paper presents a type system with subtyping for Tom, that is compatible
with Java's type system, and that performs both type checking and type
inference. We propose an algorithm that checks if all patterns of a Tom program
are well-typed. In addition, we propose an algorithm based on equality and
subtyping constraints that infers types of variables occurring in a pattern.
Both algorithms are exemplified and the proposed type system is showed to be
sound and complete
What are the early degrees of freedom in ultra-relativistic nucleus-nucleus collisions?
The Parton-Hadron-String-Dynamics (PHSD) transport model is used to study the
impact on the choice of initial degrees of freedom on the final hadronic and
electromagnetic observables in Au+Au collisions at = 200 GeV.
We find that a non-perturbative system of massive gluons (scenario I) and a
system dominated by quarks and antiquarks (scenario II) lead to different
hadronic observables when imposing the same initial energy-momentum tensor
just after the passage of the impinging nuclei. In case of the
gluonic initial condition the formation of pairs in the QGP
proceeds rather slow such that the anti-strange quarks and accordingly the
mesons do not achieve chemical equilibrium even in central Au+Au
collisions at = 200 GeV. Accordingly, the rapidity
distribution is suppressed in the gluonic scenario and in conflict with the
data from the BRAHMS Collaboration. The proton and antiproton rapidity
distributions also disfavor the scenario I. Furthermore, a clear suppression of
direct photon and dilepton production is found for the pure gluonic initial
conditions which is not so clearly seen in the present photon and dilepton
spectra from Au+Au collisions at = 200 GeV due to a large
contribution from other channels. It is argued that dilepton spectra in the
invariant mass range 1.2 GeV 3 GeV will provide a definitive answer
once the background from correlated -meson decays is subtracted
experimentally.Comment: 9 pages, 9 figure
Towards Fully Dynamic Surface Illumination in Real-Time Rendering using Acceleration Data Structures
The improvements in GPU hardware, including hardware-accelerated ray tracing, and the push for fully dynamic realistic-looking video games, has been driving more research in the use of ray tracing in real-time applications. The work described in this thesis covers multiple aspects such as optimisations, adapting existing offline methods to real-time constraints, and adding effects which were hard to simulate without the new hardware, all working towards a fully dynamic surface illumination rendering in real-time.Our first main area of research concerns photon-based techniques, commonly used to render caustics. As many photons can be required for a good coverage of the scene, an efficient approach for detecting which ones contribute to a pixel is essential. We improve that process by adapting and extending an existing acceleration data structure; if performance is paramount, we present an approximation which trades off some quality for a 2–3× improvement in rendering time. The tracing of all the photons, and especially when long paths are needed, had become the highest cost. As most paths do not change from frame to frame, we introduce a validation procedure allowing the reuse of as many as possible, even in the presence of dynamic lights and objects. Previous algorithms for associating pixels and photons do not robustly handle specular materials, so we designed an approach leveraging ray tracing hardware to allow for caustics to be visible in mirrors or behind transparent objects.Our second research focus switches from a light-based perspective to a camera-based one, to improve the picking of light sources when shading: photon-based techniques are wonderful for caustics, but not as efficient for direct lighting estimations. When a scene has thousands of lights, only a handful can be evaluated at any given pixel due to time constraints. Current selection methods in video games are fast but at the cost of introducing bias. By adapting an acceleration data structure from offline rendering that stochastically chooses a light source based on its importance, we provide unbiased direct lighting evaluation at about 30 fps. To support dynamic scenes, we organise it in a two-level system making it possible to only update the parts containing moving lights, and in a more efficient way.We worked on top of the new ray tracing hardware to handle lighting situations that previously proved too challenging, and presented optimisations relevant for future algorithms in that space. These contributions will help in reducing some artistic constraints while designing new virtual scenes for real-time applications
Imitation der Affekte und zwischenmenschliche Beziehungen
présentation et commentaire de la théorie des Affects dans la IIIe partie de l'Ethique, à partir de la théorie de l'imitation et de ses conséquences
¿Por qué Salomón?
Spinoza, que apenas reconoce predecesor alguno, parece, en ocasiones, considerar a SalomĂłn y a Pablo como verdaderos filĂłsofos spinozistas. Dejemos de lado a Pablo por esta vez. ÂżQuĂ© dice Spinoza de SalomĂłn? ÂżY cĂłmo es posible que diga lo que de Ă©l dice, cuando, por una parte, los textos que se le atribuyen carecen de la forma matemática, y, por otra, Spinoza afirma explĂcitamente que ningĂşn hebreo fue filĂłsofo?
Addendum to "Local Controllability of the Two-Link Magneto-Elastic Micro-Swimmer"
In the above mentioned note (, , published in
IEEE Trans. Autom. Cont., 2017), the first and fourth authors proved a local
controllability result around the straight configuration for a class of
magneto-elastic micro-swimmers.That result is weaker than the usual small-time
local controllability (STLC), and the authors left the STLC question open. The
present addendum closes it by showing that these systems cannot be STLC
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