Reactive GRASP for the strip-packing problem

This paper presents a greedy randomized adaptive search procedure (GRASP) for the strip packing problem, which is the problem of placing a set of rectangular pieces into a strip of a given width and infinite height so as to minimize the required height. We investigate several strategies for the constructive and improvement phases and several choices for critical search parameters. We perform extensive computational experiments with well-known instances which have been previously reported, first to select the best alternatives and then to compare the efficiency of our algorithm with other procedures. The results show that the GRASP algorithm outperforms recently reported metaheuristics.     

A parallel algorithm for constrained two-staged two-dimensional cutting problems

In this paper, we solve the two-staged two-dimensional cutting problem using a parallel algorithm. The proposed approach combines two main features: beam search (BS) and strip generation solution procedures (SGSP). BS employs a truncated tree-search, where a selected subset of generated nodes are retuned for further search. SGSP, a constructive procedure, combines a (sub)set of strips for providing both partial lower and complementary upper bounds. The algorithm explores in parallel a subset of selected nodes following the master-slave paradigm. The master processor serves to guide the search-resolution and each slave processor develops its proper way, trying a global convergence. The aim of such an approach is to show how the parallelism is able to efficiently solve large-scale instances, by providing new solutions within a consistently reduced runtime. Extensive computational testing on instances, taken from the literature, shows the effectiveness of the proposed approach.     

A high-continuity finite element model for two-dimensional elastic problems

A finite element model for the analysis of two-dimensional elastic problems is presented. The proposed discretization is based on a biquadratic interpolation for the displacement components and takes advantage of the enforcement of the interelement continuity to obtain a profitable reduction of the total number of the degrees of freedom. One node (two kinematical parameters) per element only is required.Numerical results obtained for some test problems show the accuracy of the model in analyzing both the deformations and the stress distribution.     

Numerical techniques for two-dimensional laplacian problems

Two numerical methods, an integral equation method and a conformal transformation method, are described for the solution of harmonic boundary value problems. The methods are designed to deal with problems involving curved boundaries, boundary singularities and discontinuous boundary conditions and are applied to a number of illustrative examples.     

Upon sector elements for two-dimensional problems

Different sector elements for two-dimensional problems for linear elastic analysis are developed and their utility for different types of problems is discussed. One of these elements (Type 1) fulfils the rigid body criterion for the two translatory motions as well as interelement compatibility conditions. This element is used together with a triangular element for the solution of Kirsch's problem. A considerable accuracy of the results is obtained with a relatively small number of elements.     

Case problems for problem-based pedagogical approaches: A comparative analysis

A comparative analysis of 51 case problems used in five problem-based pedagogical models was conducted to examine whether there are differences in their characteristics and the implications of such differences on the selection and generation of ill-structured case problems. The five pedagogical models were: situated learning, goal-based scenario, learning-by-design, problem-based learning and cognitive flexibility hypertext. The analysis revealed that while all case problems were authentic and multi-disciplinary, they varied across six themes for the pedagogical models examined: problem complexity, nature of problem topic, problem task, problem product, problem solving activity, and type of effort. The analysis also revealed that different kinds of case problems (e.g., dilemmas, design problems, case-analysis problems) are appropriate for different problem-based pedagogical models. These findings and their educational implications are described.     

A theory of portfolio revision: robustness and truncation problems

A set of decision criteria, different from bayesian methods is developed here, which is useful for making optimal portfolio decisions in a mean variance framework, These criteria which emphasize robustness and sensitivity to outliers are applied to revise a given size portfolio by including new securities or excluding old ones. A set of theorems is utilized to characterize situations when revisions are unnecessary due to the original portfolio being robust in some sense     

Portfolio approaches for constraint optimization problems

Within the Constraint Satisfaction Problems (CSP) context, a methodology that has proven to be particularly performant consists of using a portfolio of different constraint solvers. Nevertheless, comparatively few studies and investigations have been done in the world of Constraint Optimization Problems (COP). In this work, we provide a generalization to COP as well as an empirical evaluation of different state of the art existing CSP portfolio approaches properly adapted to deal with COP. The results obtained by measuring several evaluation metrics confirm the effectiveness of portfolios even in the optimization field, and could give rise to some interesting future research.     

Operational and complete approaches to belief revision

Two operational approaches to belief revision are presented in this paper.The rules of R-calculus are modified in order to deduce all the maximal consistent subsets.Another set of given in order to deduce all the minimal inconsistent subsets.Then a procedure,which can generate all the maximal consistent subsets,is presented.They are complete approaches,since all the maximal consistent subsets can be deduced or generated.In this paper,only the case of propositional logic is considered.     

A posteriori discontinuous finite element error estimation for two-dimensional hyperbolic problems

We analyze the discontinuous finite element errors associated with p-degree solutions for two-dimensional first-order hyperbolic problems. We show that the error on each element can be split into a dominant and less dominant component and that the leading part is O(h^p+1) and is spanned by two (p+1)-degree Radau polynomials in the x and y directions, respectively. We show that the p-degree discontinuous finite element solution is superconvergent at Radau points obtained as a tensor product of the roots of (p+1)-degree Radau polynomial. For a linear model problem, the p-degree discontinuous Galerkin solution flux exhibits a strong O(h^2p+2) local superconvergence on average at the element outflow boundary. We further establish an O(h^2p+1) global superconvergence for the solution flux at the outflow boundary of the domain. These results are used to construct simple, efficient and asymptotically correct a posteriori finite element error estimates for multi-dimensional first-order hyperbolic problems in regions where solutions are smooth.     

A numerical scheme for two-dimensional optimal control problems with memory effect

A new formulation for multi-dimensional fractional optimal control problems is presented in this article. The fractional derivatives which are coming from the formulation of the problem are defined in the Riemann–Liouville sense. Some terminal conditions are imposed on the state and control variables whose dimensions need not be the same. A numerical scheme is described by using the Grünwald–Letnikov definition to approximate the Riemann–Liouville Fractional Derivatives. The set of fractional differential equations, which are obtained after the discretization of the time domain, are solved within the Grünwald–Letnikov approximation to obtain the state and the control variable numerically. A two-dimensional fractional optimal control problem is studied as an example to demonstrate the performance of the scheme.     

The Dirichlet-to-Neumann map for two-dimensional crack problems

A coupled analytic/finite-element method is presented for two-dimensional crack problems. Two classes of problems are studied. The first considers problems where non-linear constitutive processes occur in a region near the crack tip and the remotely applied loading can be characterized by the linear elastic K-field and perhaps the T-stress. In this case, the finite-element method is applied in a circular region around the crack tip where non-linear constitutive response is occurring, and stiffness contributions associated with a numerically implemented Dirichlet-to-Neumann map are imposed on the circular boundary to account for the large surrounding elastic domain and the remote applied loading. The second class of problems considers entirely linear elastic domains with irregular external boundaries and/or complex applied loadings. Here, the discrete Dirichlet-to-Neumann map is used to represent a circular region surrounding the crack tip, and finite-elements are used for the external region. In this case the mixed mode stress intensity factors and the T-stress are retrieved from the map.     

Reduction approaches for robust shortest path problems

We investigate the uncertain versions of two classical combinatorial optimization problems, namely the Single-Pair Shortest Path Problem (SP-SPP) and the Single-Source Shortest Path Problem (SS-SPP). The former consists of finding a path of minimum length connecting two specific nodes in a finite directed graph G; the latter consists of finding the shortest paths from a fixed node to the remaining nodes of G. When considering the uncertain versions of both problems we assume that cycles may occur in G and that arc lengths are (possibly degenerating) nonnegative intervals. We provide sufficient conditions for a node and an arc to be always or never in an optimal solution of the Minimax regret Single-Pair Shortest Path Problem (MSP-SPP). Similarly, we provide sufficient conditions for an arc to be always or never in an optimal solution of the Minimax regret Single-Source Shortest Path Problem (MSS-SPP). We exploit such results to develop pegging tests useful to reduce the overall running time necessary to exactly solve both problems.     

A survey of computational approaches to three-dimensional layout problems

The component layout or packaging problem requires efficient search of large, discontinuous spaces. This survey paper reviews the state-of-the-art in product layout algorithms. The focus on optimization and geometric interference calculation strategies addresses the common aspects of the layout problem for all applications.     

Time-accelerated integral equations for twodimensional transient scattering problems

Based on the Hilbert transform, this paper presents a totally new method to obtain the time-accelerated electric field, magnetic field and combined field integral equations for the two-dimensional transient scattering problems. The computational complexity of the time-accelerated integral equations is analysed, which can be reduced to O(N_s~2NtlogNt) from the conventional O(N_s~2N_t~2). Numerical results verify the computational complexity of this time-accelerated method, and show that the time-accelerated integral equations can provide accurate and stable solutions for both the open and closed objects.     

A review on face recognition systems: recent approaches and challenges

Face recognition is an efficient technique and one of the most preferred biometric modalities for the identification and verification of individuals as compared to voice, fingerprint, iris, retina eye scan, gait, ear and hand geometry. This has over the years necessitated researchers in both the academia and industry to come up with several face recognition techniques making it one of the most studied research area in computer vision. A major reason why it remains a fast-growing research lies in its application in unconstrained environments, where most existing techniques do not perform optimally. Such conditions include pose, illumination, ageing, occlusion, expression, plastic surgery and low resolution. In this paper, a critical review on the different issues of face recognition systems are presented, and different approaches to solving these issues are analyzed by presenting existing techniques that have been proposed in the literature. Furthermore, the major and challenging face datasets that consist of the different facial constraints which depict real-life scenarios are also discussed stating the shortcomings associated with them. Also, recognition performance on the different datasets by researchers are also reported. The paper is concluded, and directions for future works are highlighted.

     

Cluster ensembles: A survey of approaches with recent extensions and applications

Cluster ensembles have been shown to be better than any standard clustering algorithm at improving accuracy and robustness across different data collections. This meta-learning formalism also helps users to overcome the dilemma of selecting an appropriate technique and the corresponding parameters, given a set of data to be investigated. Almost two decades after the first publication of a kind, the method has proven effective for many problem domains, especially microarray data analysis and its down-streaming applications. Recently, it has been greatly extended both in terms of theoretical modelling and deployment to problem solving. The survey attempts to match this emerging attention with the provision of fundamental basis and theoretical details of state-of-the-art methods found in the present literature. It yields the ranges of ensemble generation strategies, summarization and representation of ensemble members, as well as the topic of consensus clustering. This review also includes different applications and extensions of cluster ensemble, with several research issues and challenges being highlighted.     

A recent survey on computational techniques for solving singularly perturbed boundary value problems

This survey paper contains a surprisingly large amount of material and indeed can serve as an introduction to some of ideas and methods of singular perturbation theory. In continuation of a survey performed earlier, this paper limits its coverage to some standard numerical methods developed by numerous researchers between 2000 and 2005. A summary of the results of some recent methods is presented and this leads to conclusions and recommendations regarding methods to use on singular perturbation problems. Because of space constraints, we considered one-dimensional singularly perturbed boundary value problems only.     

Knowledge-based approaches for scheduling problems: a survey

Recent developments in artificial intelligence (AI) have led to the use of knowledge-based techniques for solving scheduling problems. The authors survey several existing intelligent planning and scheduling systems with the aim of providing a guide to the main AI techniques used. In view of the prevailing difference is usage of the terms planning and scheduling between AI and operations research (OR), a taxonomy of planning and scheduling problems is presented. The modeling of real world problems from closed deterministic worlds to complex real worlds is illustrated with a project scheduling example. Some of the more successful planning and scheduling systems are surveyed, and their features are highlighted. The AI approaches are consolidated into knowledge representation and problem solving in the project management context