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101.
Michael Buro Hans Kleine Büning 《Annals of Mathematics and Artificial Intelligence》1996,18(2):243-260
We investigate properties ofk-resolution, a restricted version of resolution in which one parent clause must have length at mostk. Starting from a unit-preference strategy, we compare minimal proof lengths of unit-resolution and unrestricted resolution. In particular, we show that the speed-up by using resolution is bound by
if the shortest unit-resolution refutation needst steps. Next we present an algorithm which decides whether the empty clause can be deduced by 2-resolution from a formula and has time complexity O(length()4). Finally we describe effects onk-resolution if a formula is transformed intot-CNF and show that extended 3-resolution is complete and sound. 相似文献
102.
Haptic texture represents the fine-grained attributes of an object's surface and is related to physical characteristics such as roughness and stiffness. We introduce an interactive and mobile scanning system for the acquisition and synthesis of haptic textures that consists of a visually tracked handheld touch probe. The most novel aspect of our work is an estimation method for the contact stiffness of an object based solely on the acceleration and forces measured during stroking of its surface with the handheld probe. We establish an experimental relationship between the estimated stiffness and the contact stiffness observed during compression. We also measure the height-displacement profile of an object's surface enabling us to generate haptic textures. We show an example of mapping the textures on to a coarse surface mesh obtained with an image-based technique, but the textures may also be combined with coarse surface meshes obtained by manual modeling. 相似文献
103.
This paper is the first attempt to successfully design efficient approximation algorithms for the single-machine weighted
flow-time minimization problem when jobs have different release dates and weights equal to their processing times under the
assumption that one job is fixed (i.e., the machine is unavailable during a fixed interval corresponding to the fixed job).
Our work is motivated by an interesting algorithmic application to the generation of valid inequalities in a branch-and-cut
method. Our analysis shows that the trivial FIFO sequence can lead to an arbitrary large worst-case performance bound. Hence,
we modify this sequence so that a new 2-approximation solution can be obtained for every instance and we prove the tightness
of this bound. Then, we propose a fully polynomial-time approximation algorithm with efficient running time for the considered
problem. Especially, the complexity of our algorithm is strongly polynomial. 相似文献
104.
Hans De Sterck Killian Miller Geoffrey Sanders 《Computing and Visualization in Science》2011,14(2):51-65
Recently, it was shown how the convergence of a class of multigrid methods for computing the stationary distribution of sparse,
irreducible Markov chains can be accelerated by the addition of an outer iteration based on iterant recombination. The acceleration
was performed by selecting a linear combination of previous fine-level iterates with probability constraints to minimize the
two-norm of the residual using a quadratic programming method. In this paper we investigate the alternative of minimizing
the one-norm of the residual. This gives rise to a nonlinear convex program which must be solved at each acceleration step.
To solve this minimization problem we propose to use a deep-cuts ellipsoid method for nonlinear convex programs. The main
purpose of this paper is to investigate whether an iterant recombination approach can be obtained in this way that is competitive
in terms of execution time and robustness. We derive formulas for subgradients of the one-norm objective function and the
constraint functions, and show how an initial ellipsoid can be constructed that is guaranteed to contain the exact solution
and give conditions for its existence. We also investigate using the ellipsoid method to minimize the two-norm. Numerical
tests show that the one-norm and two-norm acceleration procedures yield a similar reduction in the number of multigrid cycles.
The tests also indicate that one-norm ellipsoid acceleration is competitive with two-norm quadratic programming acceleration
in terms of running time with improved robustness. 相似文献
105.
Anita Petrick Jochen Gönsch Claudius Steinhardt Robert Klein 《Computers & Operations Research》2010,37(11):2027-2039
Revenue management with flexible products has experienced a growing interest in the academic literature within the last few years. Flexible products allow supply-side substitution between resources and can therefore help to maximize overall revenue as well as capacity utilization in markets with highly uncertain demand. This paper addresses the question of how the mathematical models which have been developed for capacity control with flexible products should be used over time to exploit the substitution opportunities, while keeping practical applicability in mind. Several dynamic control mechanisms are proposed, each of which makes use of the flexibility to a different extent. A comprehensive computational study shows the potential of the different approaches by revealing their strengths and weaknesses. 相似文献
106.
107.
Hummel M Garth C Hamann B Hagen H Joy KI 《IEEE transactions on visualization and computer graphics》2010,16(6):1319-1328
Integral surfaces are ideal tools to illustrate vector fields and fluid flow structures. However, these surfaces can be visually complex and exhibit difficult geometric properties, owing to strong stretching, shearing and folding of the flow from which they are derived. Many techniques for non-photorealistic rendering have been presented previously. It is, however, unclear how these techniques can be applied to integral surfaces. In this paper, we examine how transparency and texturing techniques can be used with integral surfaces to convey both shape and directional information. We present a rendering pipeline that combines these techniques aimed at faithfully and accurately representing integral surfaces while improving visualization insight. The presented pipeline is implemented directly on the GPU, providing real-time interaction for all rendering modes, and does not require expensive preprocessing of integral surfaces after computation. 相似文献
108.
Making changes to software systems can prove costly and it remains a challenge to understand the factors that affect the costs
of software evolution. This study sought to identify such factors by investigating the effort expended by developers to perform
336 change tasks in two different software organizations. We quantitatively analyzed data from version control systems and
change trackers to identify factors that correlated with change effort. In-depth interviews with the developers about a subset
of the change tasks further refined the analysis. Two central quantitative results found that dispersion of changed code and
volatility of the requirements for the change task correlated with change effort. The analysis of the qualitative interviews
pointed to two important, underlying cost drivers: Difficulties in comprehending dispersed code and difficulties in anticipating
side effects of changes. This study demonstrates a novel method for combining qualitative and quantitative analysis to assess
cost drivers of software evolution. Given our findings, we propose improvements to practices and development tools to manage
and reduce the costs. 相似文献
109.
In certain situations the state of a quantum system, after transmission through a quantum channel, can be perfectly restored.
This can be done by “coding” the state space of the system before transmission into a “protected” part of a larger state space,
and by applying a proper “decoding” map afterwards. By a version of the Heisenberg Principle, which we prove, such a protected
space must be “dark” in the sense that no information leaks out during the transmission. We explain the role of the Knill–Laflamme
condition in relation to protection and darkness, and we analyze several degrees of protection, whether related to error correction,
or to state restauration after a measurement. Recent results on higher rank numerical ranges of operators are used to construct
examples. In particular, dark spaces are constructed for any map of rank 2, for a biased permutations channel and for certain
separable maps acting on multipartite systems. Furthermore, error correction subspaces are provided for a class of tri-unitary
noise models. 相似文献
110.
Pathological use of computer and video games has been associated with indicators of psychosocial well-being, such as loneliness, low self-esteem, low social competence, and low life satisfaction. However, few studies have decisively demonstrated whether these indicators of psychosocial well-being are causes or consequences of pathological gaming. To address this gap in the literature, we conducted a two-wave panel study among 851 Dutch adolescents (543 gamers). Causal relations were analyzed using autoregressive structural equation models. These analyses indicated that social competence, self-esteem, and loneliness were significant predictors of pathological gaming six months later. Thus, lower psychosocial well-being can be considered an antecedent of pathological gaming among adolescent gamers. Our analyses further indicated that loneliness was also a consequence of pathological gaming. This suggests that displacement of real-world social interaction resulting from pathological use of video games may deteriorate existing relationships, which could explain the increase in adolescent gamers’ feelings of loneliness. 相似文献