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1.
Estimation of distribution algorithms (EDAs) are stochastic optimization techniques that explore the space of potential solutions by building and sampling explicit probabilistic models of promising candidate solutions. While the primary goal of applying EDAs is to discover the global optimum or at least its accurate approximation, besides this, any EDA provides us with a sequence of probabilistic models, which in most cases hold a great deal of information about the problem. Although using problem-specific knowledge has been shown to significantly improve performance of EDAs and other evolutionary algorithms, this readily available source of problem-specific information has been practically ignored by the EDA community. This paper takes the first step toward the use of probabilistic models obtained by EDAs to speed up the solution of similar problems in the future. More specifically, we propose two approaches to biasing model building in the hierarchical Bayesian optimization algorithm (hBOA) based on knowledge automatically learned from previous hBOA runs on similar problems. We show that the proposed methods lead to substantial speedups and argue that the methods should work well in other applications that require solving a large number of problems with similar structure. 相似文献
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DI Alois Lashofer DI Werner Hawle DI Florian Kaltenberger ao.Univ.-Prof. DI Bernhard Pelikan 《?sterreichische Wasser- und Abfallwirtschaft》2013,65(9-10):339-347
Since 2001 Archimedean screws have been used for commercial power generation. However, due to a lack of distribution, this comparatively new, ultra-low-head technology is essentially still a niche product. This work examines their potential, combining an operator survey, field measurements as well as laboratory tests. In extensive lab experiments, efficiencies were measured and compared for seven different screw types at varying speed-to-flow-rate combinations and inclination angles. Here, both excellent efficiencies and the impact of different parameters were observed and significant potential for improvement on the state of the art was found. This article summarizes the area of application, practical experience to date, and the latest developments concerning this highly efficient, low-maintenance, and ecologically promising low-head technology. In doing so, it also provides a well-founded basis for decision-making involving turbine selection at small hydropower sites. 相似文献
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Linkage problem, distribution estimation, and Bayesian networks 总被引:10,自引:0,他引:10
This paper proposes an algorithm that uses an estimation of the joint distribution of promising solutions in order to generate new candidate solutions. The algorithm is settled into the context of genetic and evolutionary computation and the algorithms based on the estimation of distributions. The proposed algorithm is called the Bayesian Optimization Algorithm (BOA). To estimate the distribution of promising solutions, the techniques for modeling multivariate data by Bayesian networks are used. The BOA identifies, reproduces, and mixes building blocks up to a specified order. It is independent of the ordering of the variables in strings representing the solutions. Moreover, prior information about the problem can be incorporated into the algorithm, but it is not essential. First experiments were done with additively decomposable problems with both nonoverlapping as well as overlapping building blocks. The proposed algorithm is able to solve all but one of the tested problems in linear or close to linear time with respect to the problem size. Except for the maximal order of interactions to be covered, the algorithm does not use any prior knowledge about the problem. The BOA represents a step toward alleviating the problem of identifying and mixing building blocks correctly to obtain good solutions for problems with very limited domain information. 相似文献
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We develop an approach for segmenting radiographic images of focal bone lesions possibly caused by bone tumour. A neural
network is used to classify individual pixels by a convolution operation based on a feature vector. We design eight features
that characterise the local texture in the neighbourhood of a pixel. Four of the features are based on co-occurrence matrices
computed from the neighbourhood. The true class label of the pixels in the radiographs are obtained from annotations made
by an experienced radiologist. Neural networks and self-organising feature maps are trained to perform the segmentation task.
The experiments confirm the feasibility of using a feature-based neural network for finding pathologic bone changes in radiographic
images. An analysis of the eight features indicates that the presence of edges and transitions, the complexity of the texture,
as well as the amount of high frequencies in the texture, are the main features discriminating (soft) tissue from pathologic
bone, the two classes most likely to be confused.
Receiveed: 4 June 1998?,Received in revised form: 15 September 1999?Accepted: 11 December 1998 相似文献
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Oil of Cotia, a new semi-drying oil, obtained from a Brazilian nut is described. Some chemical constants are determined and
tabulated. The high Diene Value of this oil and other properties indicate that it might be used in the paint and varnish industries. 相似文献
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Materials Science - We propose a way to increase the wear and crack resistance of the main working tools for roller mills. Bimetallic rollers (with a diameter of 252 mm and a length of 1620 mm) are... 相似文献
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a) | The study describes the basic fracture micromechanisms of porous materials with dominantly ferritic matrix structures. |
b) | Quantitative fractography is used to describe the basic mechanisms of crack propagation in the porous body corresponding to the non-monotonous temperature dependence of fracture toughness values. |
c) | Behavior of fracture toughness values and relevant fracture micromechanisms indicate that the state of plane deformation in microvolumes in front of the crack tip cannot be reached at higher porosities and temperatures. This piece of information corresponds to the knowledge of independence of fracture toughness values of porous materials on the specimen thickness, as is presented in the literature [5]. |
10.
Martin Pelikan Kumara Sastry David E. Goldberg 《Genetic Programming and Evolvable Machines》2008,9(1):53-84
Efficiency enhancement techniques—such as parallelization and hybridization—are among the most important ingredients of practical
applications of genetic and evolutionary algorithms and that is why this research area represents an important niche of evolutionary
computation. This paper describes and analyzes sporadic model building, which can be used to enhance the efficiency of the hierarchical Bayesian optimization algorithm (hBOA) and other estimation
of distribution algorithms (EDAs) that use complex multivariate probabilistic models. With sporadic model building, the structure
of the probabilistic model is updated once in every few iterations (generations), whereas in the remaining iterations, only
model parameters (conditional and marginal probabilities) are updated. Since the time complexity of updating model parameters
is much lower than the time complexity of learning the model structure, sporadic model building decreases the overall time
complexity of model building. The paper shows that for boundedly difficult nearly decomposable and hierarchical optimization
problems, sporadic model building leads to a significant model-building speedup, which decreases the asymptotic time complexity of model building in hBOA by a factor of to where n is the problem size. On the other hand, sporadic model building also increases the number of evaluations until convergence;
nonetheless, if model building is the bottleneck, the evaluation slowdown is insignificant compared to the gains in the asymptotic complexity of model building. The paper also presents a dimensional
model to provide a heuristic for scaling the structure-building period, which is the only parameter of the proposed sporadic
model-building approach. The paper then tests the proposed method and the rule for setting the structure-building period on
the problem of finding ground states of 2D and 3D Ising spin glasses. 相似文献