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Solution Methods (solution + methods)
Kinds of Solution Methods Selected AbstractsSocial Infrastructure Planning: A Location Model and Solution MethodsCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 8 2007João F. Bigotte Authorities want to determine where to locate the facilities of a social infrastructure network and what should be the capacity of these facilities. Each user must be assigned to its closest facility and, to be economically viable, each facility must serve at least a pre-specified level of demand. The objective is to maximize the accessibility to facilities (i.e., to minimize the distance traveled by users to reach the facilities). A location model that captures the above features is formulated and different solution methods are tested. Among the methods tested, tabu search and a specialized local search heuristic provided the best solutions. The application of the model is illustrated through a case study involving the location of preschools in the municipality of Miranda do Corvo, Portugal. [source] Optimal Control of Iterative Solution Methods for Linear Systems of EquationsPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2005Uwe Helmke Iterative solution methods for linear systems of equations can be regarded as discrete-time control systems, for which a stabilizing feedback control has to be found. Well known algorithms such as GMRES(m) may exhibit unstable dynamics or sensitive dependence on initial conditions, thus preventing the algorithm to converge to the desired solution. Based on linear system feedback design techniques a new algorithm is proposed that does not suffer under such shortcomings. Global convergence to the desired solution is shown for any initial state. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Geomechanics and Tunnelling 2/2010GEOMECHANICS AND TUNNELLING, Issue 1 2010Article first published online: 24 FEB 2010 Semmering and Koralm tunnels Neue Südbahn, Semmering und Koralm Tunnel F. Bauer: Investment in the Austrian rail network , overview of new and upgrading projects , Investitionen in das österreichische Schienennetz , Überblick Neu- und Ausbauvorhaben G. Gobiet and D. Haas: New Semmering Base Tunnel project , an interdisciplinary challenge , Semmering Basistunnel Neu , eine interdisziplinäre Herausforderung A. Fasching, R. Vanek, Th. Stadlmann, P. Reichl, G. Domberger, G. Forstinger and O. Wagner: New Semmering Base Tunnel , the investigation programme 2008/2009 and the knowledge gained in the areas of geology, hydrogeology and geotechnical engineering , Semmering-Basistunnel Neu , Das Erkundungsprogramm 2008/2009 und die daraus gewonnenen Erkenntnisse auf den Gebieten der Geologie, Hydrogeologie und Geotechnik J. Daller, A. Vigl and O. Wagner: New Semmering Base Tunnel , the current state of tunnel design taking the newest investigation results into account , Semmering-Basistunnel Neu , Aktueller Stand der Tunnelplanung unter Berücksichtigung der neuesten Erkundungsergebnisse R. Bopp, V. Langer, Ch. Neumann and O. Wagner: The ventilation and tunnel safety concept for the New Semmering Base Tunnel , Das Lüftungs- und Tunnelsicherheitskonzept für den Semmering-Basistunnel Neu G. Harer and J. Koinig: Current state of design, investigation and construction work at the Koralm Tunnel , Aktueller Stand der Planungs-, Erkundungs- und Ausführungsarbeiten beim Koralmtunnel P. Schubert, H. Hölzl, P. Sellner and F. Fasching: Geomechanical knowledge gained from the Paierdorf Investigation Tunnel in the section through the Lavanttal main fault zone , Geomechanischer Wissenszuwachs durch den Erkundungstunnel Paierdorf im Abschnitt der Lavanttaler Hauptstörungszone D. Handke, M. Nolden, K. Mussger and A. Steidl: Solution methods for the design and construction of contract KAT 3 , Lösungsansätze für Planung und Bauausführung des Bauloses KAT 3 M. Vill, H. Wagner, A. Schweighofer, H. Huber, W. Pichler and J. Kollegger: New development of a crack-limited invert slab , Neuentwicklung der rissebeschränkten Sohlplatte M. Stopka: Hengsberg Tunnel , the construction contract as seen by the contractor , Hengsbergtunnel , der Bauvertrag aus Sicht des Auftragnehmers T. Schachinger, H. Gaube and G. Krainer: Results from the Untersammelsdorf test field for the planning of the tunnelling work , Erkenntnisse aus dem Versuchsfeld Untersammelsdorf für die Gestaltung der Vortriebsmaßnahmen K. Chmelina and K. Rabensteiner: Improvement of the safety and profitability of tunnel drives through the use of automated measurement and alarm systems , examples in practice , Verbesserung der Sicherheit und Wirtschaftlichkeit von Tunnelvortrieben durch den Einsatz automatisierter Mess- und Alarm-systeme , Ausführungsbeispiele [source] Emergency service systems: The use of the hypercube queueing model in the solution of probabilistic location problemsINTERNATIONAL TRANSACTIONS IN OPERATIONAL RESEARCH, Issue 5 2008Roberto D. Galvão Abstract Probabilistic location problems are surveyed from the perspective of their use in the design of emergency service systems, with special emphasis on emergency medical systems. Pioneering probabilistic models were defined in the 1980s, as a natural extension of deterministic covering models (first generation models) and backup models (second generation). These probabilistic models, however, adopted simplifying assumptions that in many cases do not correspond to real-world situations, where servers usually cooperate and have specific individual workloads. Thus the idea of embedding the hypercube queueing model into these formulations is to make them more adherent to the real world. The hypercube model and its extensions are initially presented in some detail, which is followed by a brief review of exact and approximate methods for its solution. Probabilistic models for the design of emergency service systems are then reviewed. The pioneering models of Daskin and ReVelle and Hogan are extended by embedding the hypercube model into them. Solution methods for these models are surveyed next, with comments on specialized models for the design of emergency medical systems for urban areas and highways. [source] A mean-variance model for the minimum cost flow problem with stochastic arc costsNETWORKS: AN INTERNATIONAL JOURNAL, Issue 3 2010Stephen D. Boyles Abstract This article considers a minimum cost flow problem where arc costs are uncertain, and the decision maker wishes to minimize both the expected flow cost and the variance of this cost. Two optimality conditions are given, one based on cycle marginal costs, and another based on concepts of network equilibrium. Solution methods are developed based on these conditions. The value of information is also studied, and efficient approximation techniques are developed for the specific case of learning the exact cost of one or more arcs a priori. Finally, numerical results compare the solution methods developed in this work: the minimum mean cycle canceling algorithm performs better on all of the networks tested, although the equilibrium-based algorithm is more competitive for large networks. Solution sensitivity to input parameters is also examined, as is the performance of the approximation techniques for the value of information. Approximation techniques based on arc cost distributions were found to outperform those based on properties of optimal flows. © 2009 Wiley Periodicals, Inc. NETWORKS, 2010 [source] Solution methods for the p -median problem: An annotated bibliographyNETWORKS: AN INTERNATIONAL JOURNAL, Issue 3 2006J. Reese Abstract The p -median problem is a network problem that was originally designed for, and has been extensively applied to, facility location. In this bibliography, we summarize the literature on solution methods for the uncapacitated and capacitated p -median problem on a network. © 2006 Wiley Periodicals, Inc. NETWORKS, Vol. 48(3), 125,142 2006 [source] On introducing approximate solution methods in theory of elasticityCOMPUTER APPLICATIONS IN ENGINEERING EDUCATION, Issue 2 2006Autar Kaw Abstract This work presents how approximate solution methods were introduced in a graduate level course of Theory of Elasticity. The three methods introduced are the finite difference method, the finite element method, and the boundary element method. All methods are exemplified by the problem of a thick-walled cylinder subject to internal pressure with an axisymmetric response. Choosing a single problem to introduce the three methods demonstrates accuracy and efficacy of each method. © 2006 Wiley Periodicals, Inc. Comput Appl Eng Educ 14: 120,134, 2006; Published online in Wiley InterScience (www.interscience.wiley.com); DOI 10.1002/cae.20070 [source] Time-dependent groundwater modeling using spreadsheetCOMPUTER APPLICATIONS IN ENGINEERING EDUCATION, Issue 3 2005Halil Karahan Abstract Time-dependent groundwater modeling using spreadsheet simulation (TGMSS) model is developed as solution technique. It is a practical method that uses spreadsheets instead of the conventional solution methods. All of the aquifer parameters can easily be described in TGMSS model. The results of TGMSS are validated with MODFLOW. Results showed that TGMSS and MODFLOW results were in good agreement in terms of resulting values of hydraulic heads. © 2005 Wiley Periodicals, Inc. Comput Appl Eng Educ 13: 192,199, 2005; Published online in Wiley InterScience (www.interscience.wiley.com); DOI 10.1002/cae.20048 [source] Social Infrastructure Planning: A Location Model and Solution MethodsCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 8 2007João F. Bigotte Authorities want to determine where to locate the facilities of a social infrastructure network and what should be the capacity of these facilities. Each user must be assigned to its closest facility and, to be economically viable, each facility must serve at least a pre-specified level of demand. The objective is to maximize the accessibility to facilities (i.e., to minimize the distance traveled by users to reach the facilities). A location model that captures the above features is formulated and different solution methods are tested. Among the methods tested, tabu search and a specialized local search heuristic provided the best solutions. The application of the model is illustrated through a case study involving the location of preschools in the municipality of Miranda do Corvo, Portugal. [source] Review of the Integrated Groundwater and Surface-Water Model (IGSM)GROUND WATER, Issue 2 2003Eric M. LaBolle Development of the finite-element-based Integrated Groundwater and Surface-Water Model (IGSM) began in the 1970s. Its popularity grew in the early 1990s with its application to California's Central Valley Groundwater Surface-Water Model in support of the Central Valley Project Improvement Act. Since that time, IGSM has been applied by federal, state, and local agencies to model a number of major basins in California. Our review of the recently released version 5.0 of IGSM reveals a solution methodology that deviates from established solution techniques, potentially compromising its reliability under many circumstances. One difficulty occurs because of the semi-explicit time discretization used. Combined with the fixed monthly time step of IGSM, this approach can prevent applications from accurately converging when using parameter values typically found in nature. Additionally, IGSM fails to properly couple and simultaneously solve ground water and surface water models with appropriate mass balance and head convergence under the reasonable conditions considered herein. As a result, IGSM-predicted streamflow is error prone, and errors could exceed 100%. IGSM does not inform the user that there may be a convergence problem with the solution, but instead generally reports good mass balance. Although our review touches on only a few aspects of the code, which exceeds 17,000 lines, our experience is that similar problems arise in other parts of IGSM. Review and examples demonstrate the potential consequences of using the solution methods in IGSM for the prediction, planning, and management of water resources, and provide perspective on the roles of standards and code validation in ground water modeling. [source] Rank deficiency in superconvergent patch recovery techniques with 4-node quadrilateral elementsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 1 2007Z. Yue Abstract The linear systems of equations generated by the Superconvergent Patch Recovery technique (Int. J. Numer. Methods Eng. 1992; 33:1331,1382; Comput. Methods Appl. Mech. Eng. 1992; 101:207,224) can exhibit rank deficiency under certain purely geometric conditions. The rank deficiency problem can be corrected simply and efficiently by utilizing a local rotated co-ordinate system. This rotated SPR procedure is easily automated and adds robustness to automatic adaptive solution methods. Copyright © 2006 John Wiley & Sons, Ltd. [source] Algebraic preconditioning versus direct solvers for dense linear systems as arising in crack propagation problemsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 2 2005Erik Bängtsson Abstract Preconditioned iterative solution methods are compared with the direct Gaussian elimination method to solve dense linear systems Ax=b which originate from problems, discretized by boundary element method (BEM) techniques. Numerical experiments are presented and compared with the direct solution method available in a commercial BEM package, which show that the preconditioned iterative schemes are highly competitive with respect to both arithmetic operations required and memory demands. Copyright © 2004 John Wiley & Sons, Ltd. [source] A cut-cell non-conforming Cartesian mesh method for compressible and incompressible flowINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 11 2007J. Pattinson Abstract This paper details a multigrid-accelerated cut-cell non-conforming Cartesian mesh methodology for the modelling of inviscid compressible and incompressible flow. This is done via a single equation set that describes sub-, trans-, and supersonic flows. Cut-cell technology is developed to furnish body-fitted meshes with an overlapping mesh as starting point, and in a manner which is insensitive to surface definition inconsistencies. Spatial discretization is effected via an edge-based vertex-centred finite volume method. An alternative dual-mesh construction strategy, similar to the cell-centred method, is developed. Incompressibility is dealt with via an artificial compressibility algorithm, and stabilization achieved with artificial dissipation. In compressible flow, shocks are captured via pressure switch-activated upwinding. The solution process is accelerated with full approximation storage (FAS) multigrid where coarse meshes are generated automatically via a volume agglomeration methodology. This is the first time that the proposed discretization and solution methods are employed to solve a single compressible,incompressible equation set on cut-cell Cartesian meshes. The developed technology is validated by numerical experiments. The standard discretization and alternative methods were found equivalent in accuracy and computational cost. The multigrid implementation achieved decreases in CPU time of up to one order of magnitude. Copyright © 2007 John Wiley & Sons, Ltd. [source] Accelerating iterative solution methods using reduced-order models as solution predictorsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 5 2006R. Markovinovi Abstract We propose the use of reduced-order models to accelerate the solution of systems of equations using iterative solvers in time stepping schemes for large-scale numerical simulation. The acceleration is achieved by determining an improved initial guess for the iterative process based on information in the solution vectors from previous time steps. The algorithm basically consists of two projection steps: (1) projecting the governing equations onto a subspace spanned by a low number of global empirical basis functions extracted from previous time step solutions, and (2) solving the governing equations in this reduced space and projecting the solution back on the original, high dimensional one. We applied the algorithm to numerical models for simulation of two-phase flow through heterogeneous porous media. In particular we considered implicit-pressure explicit-saturation (IMPES) schemes and investigated the scope to accelerate the iterative solution of the pressure equation, which is by far the most time-consuming part of any IMPES scheme. We achieved a substantial reduction in the number of iterations and an associated acceleration of the solution. Our largest test problem involved 93 500 variables, in which case we obtained a maximum reduction in computing time of 67%. The method is particularly attractive for problems with time-varying parameters or source terms. Copyright © 2006 John Wiley & Sons, Ltd. [source] A comparison of preconditioners for incompressible Navier,Stokes solversINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 12 2008M. ur Rehman Abstract We consider solution methods for large systems of linear equations that arise from the finite element discretization of the incompressible Navier,Stokes equations. These systems are of the so-called saddle point type, which means that there is a large block of zeros on the main diagonal. To solve these types of systems efficiently, several block preconditioners have been published. These types of preconditioners require adaptation of standard finite element packages. The alternative is to apply a standard ILU preconditioner in combination with a suitable renumbering of unknowns. We introduce a reordering technique for the degrees of freedom that makes the application of ILU relatively fast. We compare the performance of this technique with some block preconditioners. The performance appears to depend on grid size, Reynolds number and quality of the mesh. For medium-sized problems, which are of practical interest, we show that the reordering technique is competitive with the block preconditioners. Its simple implementation makes it worthwhile to implement it in the standard finite element method software. Copyright © 2007 John Wiley & Sons, Ltd. [source] Extension of a combined analytical/numerical initial value problem solver for unsteady periodic flowINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 9 2002Lawrence J. De Chant Abstract Here we describe analytical and numerical modifications that extend the Differential Reduced Ejector/ mixer Analysis (DREA), a combined analytical/numerical, multiple species ejector/mixing code developed for preliminary design applications, to apply to periodic unsteady flow. An unsteady periodic flow modelling capability opens a range of pertinent simulation problems including pulse detonation engines (PDE), internal combustion engine ICE applications, mixing enhancement and more fundamental fluid dynamic unsteadiness, e.g. fan instability/vortex shedding problems. Although mapping between steady and periodic forms for a scalar equation is a classical problem in applied mathematics, we will show that extension to systems of equations and, moreover, problems with complex initial conditions are more challenging. Additionally, the inherent large gradient initial condition singularities that are characteristic of mixing flows and that have greatly influenced the DREA code formulation, place considerable limitations on the use of numerical solution methods. Fortunately, using the combined analytical,numerical form of the DREA formulation, a successful formulation is developed and described. Comparison of this method with experimental measurements for jet flows with excitation shows reasonable agreement with the simulation. Other flow fields are presented to demonstrate the capabilities of the model. As such, we demonstrate that unsteady periodic effects can be included within the simple, efficient, coarse grid DREA implementation that has been the original intent of the DREA development effort, namely, to provide a viable tool where more complex and expensive models are inappropriate. Copyright © 2002 John Wiley & Sons, Ltd. [source] LS-DYNA and the 8:1 differentially heated cavityINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 8 2002Mark A. Christon Abstract This paper presents results computed using LS-DYNA's new incompressible flow solver for a differentially heated cavity with an 8:1 aspect ratio at a slightly super-critical Rayleigh number. Three Galerkin-based solution methods are applied to the 8:1 thermal cavity on a sequence of four grids. The solution methods include an explicit time-integration algorithm and two second-order projection methods,one semi-implicit and the other fully implicit. A series of ad hoc modifications to the basic Galerkin finite element method are shown to result in degraded solution quality with the most serious effects introduced by row-sum lumping the mass matrix. The inferior accuracy of a lumped mass matrix relative to a consistent mass matrix is demonstrated with the explicit algorithm which fails to obtain a transient solution on the coarsest grid and exhibits a general trend to under-predict oscillation amplitudes. The best results are obtained with semi-implicit and fully implicit second-order projection methods where the fully implicit method is used in conjunction with a ,smart' time integrator. Copyright © 2002 John Wiley & Sons, Ltd. [source] Optimization models and solution methods for load managementINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 4 2004Stig-Inge Gustafsson Abstract The electricity market in Sweden has changed during recent years. Electricity for industrial use can now be purchased from a number of competing electricity suppliers. Hence, the price for each kilowatt-hour is significantly lower than it was just two years ago and interest in electricity conservation measures has declined. However, part of the electricity tariff, i.e. the demand cost expressed in Swedish Kronor (SEK) for each kilowatt, is almost the same as before. Attention has thereby been drawn to load management measures in order to reduce this specific cost. Saving one kWh might lead to a monetary saving of between SEK 0.22 and SEK 914; this paper demonstrates how to eliminate only those kWh that actually save a significant amount of money. A load management system has been installed in a small carpentry factory that can turn off equipment based on a pre-set priority and number of minutes each hour. The question now is what level of the electricity load is optimal in a strictly mathematical sense, i.e. how many kW should be set in the load management computer in order to maximise profitability? In this paper, we develop a mathematical model that can be used as a tool both to find the most profitable subscription level and to control the choices to be made. Numerical results from a case study are presented. Copyright © 2004 John Wiley & Sons, Ltd. [source] An investigation of genetic algorithms for the optimization of multi-objective fisheries bioeconomic modelsINTERNATIONAL TRANSACTIONS IN OPERATIONAL RESEARCH, Issue 1 2000S.J. Mardle Abstract The use of genetic algorithms (GA) for optimization problems offers an alternative approach to the traditional solution methods. GA follow the concept of solution evolution, by stochastically developing generations of solution populations using a given fitness statistic, for example the achievement function in goal programs. They are particularly applicable to problems which are large, non-linear and possibly discrete in nature, features that traditionally add to the degree of complexity of solution. Owing to the probabilistic development of populations, GA do not distinguish solutions, e.g. local optima from other solutions, and therefore cannot guarantee optimality even though a global optimum may be reached. In this paper, a non-linear goal program of the North Sea demersal fisheries is used to develop a genetic algorithm for optimization. Comparisons between the GA approach and traditional solution methods are made, in order to measure the relative effectiveness. General observations of the use of GA in multi-objective fisheries bioeconomic models, and other similar models, are discussed. [source] Private road competition and equilibrium with traffic equilibrium constraintsJOURNAL OF ADVANCED TRANSPORTATION, Issue 1 2009Hai Yang Abstract Toll road competition is one of the important issues under a build-operate-transfer (BOT) scheme, which is being encountered nowadays in many cities. When there are two or more competing firms and each firm operates a competitive toll road, their profits are interrelated due to the competitors' choices and demand inter-dependence in the network. In this paper we develop game-theoretic approaches to the study of the road network, on which multiple toll roads are operated by competitive private firms. The strategic interactions and market equilibria among the private firms are analyzed both in determining their supply (road capacity) and price (toll level) over the network. The toll road competition problems in general traffic equilibrium networks are formulated as an equilibrium program with equilibrium constraints or bi-level variational inequalities. Heuristic solution methods are proposed and their convergences are demonstrated with simple network examples. It is shown that private pricing and competition can be both profitable and welfare-improving. [source] One-dimensional model of vacuum filtration of compressible flocculated suspensionsAICHE JOURNAL, Issue 10 2010Anthony D. Stickland Abstract This work details the one-dimensional modeling of the different processes that may occur during the vacuum filtration of compressible flocculated suspensions. Depending on the operating conditions of the applied pressure and the initial solids concentration relative to the material properties of the compressive yield stress and the effective capillary pressure at the air,liquid interface, the dewatering process undergoes a combination of cake formation, consolidation, and/or desaturation. Mathematical models for these processes based on the compressional rheology approach are presented and appropriate solution methods outlined. Results using customary material properties are given for different operating conditions to illustrate the three dewatering processes. This approach lays the theoretical basis for further work understanding two- and three-dimensional effects during desaturation, such as cracking and wall detachment. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source] Hybrid ,/,3 -peptides with proteinogenic side chains. monosubstituted analogues of the chemotactic tripeptide For-Met-Leu-Phe-OMeJOURNAL OF PEPTIDE SCIENCE, Issue 8 2004Cesare Giordano Abstract The ,/,3 -mixed tripeptides R-CO-,3 -HMet-Leu-Phe-OMe (1a,b), R-CO-Met-,3 -HLeu-Phe-OMe (2a,b) and R-CO-Met-Leu-,3 -HPhe-OMe (3a,b) (a, R = tert -butyloxy-; b, R = H,), analogues of the potent chemoattractant For-Met-Leu-Phe-OMe, have been synthesized by classical solution methods and fully characterized. The activities of the new analogues as chemoattractants, superoxide anion producers and lysozyme releasers have been determined on human neutrophils. Whereas all of the three N -formyl derivatives are significantly less active than the parent tripeptide as chemoattractants, compound 1b has been found to be highly active as a superoxide anion producer and 3b as a lysozyme releaser. The results show that the replacement of the native Leu residue at the central position is, in each of the examined cases, the least favourable modification. The three N -Boc derivatives are, as expected, devoid of activity as agonists, but they are all good inhibitors of chemotaxis. Information on the solution conformation has been obtained by examining the involvement of the NH groups in intramolecular H-bonds using 1H NMR. The conformation of the N -Boc analogue 1a has also been determined in the crystal state by x-ray diffraction analysis. The molecule is extended at the ,3 -HMet residue (,1 = ,87°;,1 = 172°;,1 = 126° ) and no intramolecular H-bond is present. Copyright © 2004 European Peptide Society and John Wiley & Sons, Ltd. [source] Explicitly Teaching for Transfer: Effects on the Mathematical Problem-Solving Performance of Students with Mathematics DisabilitiesLEARNING DISABILITIES RESEARCH & PRACTICE, Issue 2 2002Lynn S. Fuchs The purpose of this study was to explore methods to enhance mathematical problem solving for students with mathematics disabilities (MD). A small-group problem-solving tutoring treatment incorporated explicit instruction on problem-solution rules and on transfer. The transfer component was designed to increase awareness of the connections between novel and familiar problems by broadening the categories by which students group problems requiring the same solution methods and by prompting students to search novel problems for these broad categories. To create a stringent test of efficacy, we incorporated a computer-assisted practice condition, which provided students with direct practice on real-world problem-solving tasks. We randomly assigned 40 students to problem-solving tutoring, computer-assisted practice, problem-solving tutoring plus computer-assisted practice, or control, and pre- and posttested students on three problem-solving tasks. On story problems and transfer story problems, tutoring (with or without computer-assisted practice) effected reliably stronger growth compared to control; effects on real-world problem solving, although moderate to large, were not statistically significant. Computer-assisted practice added little value beyond tutoring but, alone, yielded moderate effects on two measures. [source] A trust-region method with a conic model for unconstrained optimizationMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 15 2008Shao-Jian Qu Abstract In this paper, we propose and analyze a new conic trust-region algorithm for solving the unconstrained optimization problems. A new strategy is proposed to construct the conic model and the relevant conic trust-region subproblems are solved by an approximate solution method. This approximate solution method is not only easy to implement but also preserves the strong convergence properties of the exact solution methods. Under reasonable conditions, the locally linear and superlinear convergence of the proposed algorithm is established. The numerical experiments show that this algorithm is both feasible and efficient. Copyright © 2008 John Wiley & Sons, Ltd. [source] Sparse factorization of finite element matrices using overlapped localizing solution modesMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 4 2008J.-S. Choi Abstract Local-global solution (LOGOS) modes provide a computationally efficient framework for developing fast, direct solution methods for electromagnetic simulations. In this article, we demonstrate that the LOGOS framework yields fast direct solutions for finite element discretizations of the wave equation in two dimensions. For fixed-frequency applications, numerical examples demonstrate that the memory and CPU complexities of the proposed solver are nearly linear. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1050,1054, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23298 [source] Flexibility and complexity in periodic distribution problemsNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 2 2007Peter Francis Abstract In this paper, we explore trade-offs between operational flexibility and operational complexity in periodic distribution problems. We consider the gains from operational flexibility in terms of vehicle routing costs and customer service benefits, as well as the costs of operational complexity in terms of modeling, solution methods, and implementation challenges for drivers and customers. The period vehicle routing problem (PVRP) is a variation of the classic vehicle routing problem in which delivery routes are constructed for a period of time; the PVRP with service choice (PVRP-SC) extends the PVRP to allow service (visit) frequency to become a decision of the model. For the periodic distribution problems represented by PVRP and PVRP-SC, we introduce operational flexibility levers and a set of quantitative measures to evaluate the trade-offs between flexibility and complexity. We develop a Tabu Search heuristic to incorporate a range of operational flexibility options. We analyze the potential value and the increased operational complexity of the flexibility levers. © 2006 Wiley Periodicals, Inc. Naval Research Logistics, 2007 [source] New heuristic methods for the capacitated multi-facility Weber problemNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 1 2007Necati Aras Abstract In this paper we consider the capacitated multi-facility Weber problem with the Euclidean, squared Euclidean, and ,p -distances. This problem is concerned with locating m capacitated facilities in the Euclidean plane to satisfy the demand of n customers with the minimum total transportation cost. The demand and location of each customer are known a priori and the transportation cost between customers and facilities is proportional to the distance between them. We first present a mixed integer linear programming approximation of the problem. We then propose new heuristic solution methods based on this approximation. Computational results on benchmark instances indicate that the new methods are both accurate and efficient. © 2006 Wiley Periodicals, Inc. Naval Research Logistics 2006 [source] Maximizing project cash availabilityNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 4 2006Joseph G. Szmerekovsky Abstract Consider a project during the life cycle of which there are cash payouts and in-flows. To better meet his financial commitments, the project owner would like to meet all deadlines without running out of cash. We show that the cash availability objective is similar to the total weighted flowtime used to measure work-in-progress performance in the scheduling and inventory control literatures. In this article we provide several specialized solution methods for the problem of minimizing total weighted flowtime in an arbitrary acyclic project network, subject to activity release times and due dates, where the activity weights may be positive or negative and represent cash in- and out-flows. We describe the structure of an optimal solution and provide several efficient algorithms and their complexity based on mincost and maxflow formulations. © 2006 Wiley Periodicals, Inc. Naval Research Logistics, 2006 [source] Algorithms for the multi-item multi-vehicles dynamic lot sizing problemNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 2 2006Shoshana Anily Abstract We consider a two-stage supply chain, in which multi-items are shipped from a manufacturing facility or a central warehouse to a downstream retailer that faces deterministic external demand for each of the items over a finite planning horizon. The items are shipped through identical capacitated vehicles, each incurring a fixed cost per trip. In addition, there exist item-dependent variable shipping costs and inventory holding costs at the retailer for items stored at the end of the period; these costs are constant over time. The sum of all costs must be minimized while satisfying the external demand without backlogging. In this paper we develop a search algorithm to solve the problem optimally. Our search algorithm, although exponential in the worst case, is very efficient empirically due to new properties of the optimal solution that we found, which allow us to restrict the number of solutions examined. Second, we perform a computational study that compares the empirical running time of our search methods to other available exact solution methods to the problem. Finally, we characterize the conditions under which each of the solution methods is likely to be faster than the others and suggest efficient heuristic solutions that we recommend using when the problem is large in all dimensions. © 2005 Wiley Periodicals, Inc. Naval Research Logistics, 2006. [source] Radar pulse interleaving for multi-target trackingNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 1 2004Moustafa Elshafei Abstract In a multifunction radar, the maximum number of targets that can be managed or tracked is an important performance measure. Interleaving algorithms developed to operate radars exploit the dead-times between the transmitted and the received pulses to allocate new tracking tasks that might involve transmitting or receiving pulses, thus increasing the capacity of the system. The problem of interleaving N targets involves a search among N! possibilities, and suboptimal solutions are usually employed to satisfy the real-time constraints of the radar system. In this paper, we present new tight 0,1 integer programming models for the radar pulse interleaving problem and develop effective solution methods based on Lagrangian relaxation techniques. © 2003 Wiley Periodicals, Inc. Naval Research Logistics, 2004. 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