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OPTIMIZATION ABSTRACTS"Mathematical Models for Planning Support"
LEO KROON, Erasmus University Rotterdam (EUR) - Department of Decision and Information Sciences, Erasmus Research Institute of Management (ERIM) - Joint Research Institute of Rotterdam School of Management (RSM) and Erasmus School of Economics(ESE), EUR, NS Reizigers - Department of Logistics
In this paper we describe how computer systems can provide planners with active planning support, when these planners are carrying out their daily planning activities. This means that computer systems actively participate in the planning process by automatically generating plans or partial plans. Active planning support by computer systems requires the application of mathematical models and solution techniques. In this paper we describe the modeling process in general terms, as well as several modeling and solution techniques. We also present some background information on computational complexity theory, since most practical planning problems are hard to solve. We also describe how several objective functions can be handled, since it is rare that solutions can be evaluated by just one single objective. Furthermore, we give an introduction into the use of mathematical modeling systems, which are useful tools in a modeling context, especially during the development phases of a mathematical model. We finish the paper with a real life example related to the planning process of the rolling stock circulation of a railway operator.
"Optimization of GTAW Pulse Parameters Affecting Residual Stress in 304 Stainless Steel Weldments"
NAVNEET ARORA, Indian Institute of Technology The paper reports the effect of pulsing parameters on the magnitude of welding residual stresses by using gas tungsten arc welding on type 304 austenitic stainless steel. The problems related to residual stresses in weldments are of major concern, as they may modify the resistance to brittle fracture, fatigue strength and stress corrosion cracking of a welded part or structure. The residual stress has been determined by hole drilling strain gauge method of ASTM standard E-837. Optimization analysis has been carried out to find out the optimum magnitude of pulsing parameters, viz., amplitude ratio, pulse frequency, duration ratio and root gap corresponding to the least residual stresses. To reduce the number of samples to minimum, Taguchi experimental design technique has been used and values of the pulsing parameters at which the residual stress is minimal have been obtained. The experimental results show that a greater amplitude ratio and duration ratio can increase the magnitude of residual stresses and greater pulse frequency can reduce the magnitude of residual stresses. "Heuristic Optimisation in Financial Modelling"
MANFRED GILLI, University of Geneva, Swiss Finance Institute There is a large number of optimisation problems in theoretical and applied finance that are difficult to solve as they exhibit multiple local optima or are not 'well-behaved' in other ways (e.g., discontinuities in the objective function). One way to deal with such problems is to adjust and to simplify them, for instance by dropping constraints, until they can be solved with standard numerical methods. This paper argues that an alternative approach is the application of optimisation heuristics like Simulated Annealing or Genetic Algorithms. These methods have been shown to be capable to handle non-convex optimisation problems with all kinds of constraints. To motivate the use of such techniques in finance, the paper presents several actual problems where classical methods fail. Next, several well-known heuristic techniques that may be deployed in such cases are described. Since such presentations are quite general, the paper describes in some detail how a particular problem, portfolio selection, can be tackled by a particular heuristic method, Threshold Accepting. Finally, the stochastics of the solutions obtained from heuristics are discussed. It is shown, again for the example from portfolio selection, how this random character of the solutions can be exploited to inform the distribution of computations. "Optimised Search Heuristic Combining Valid Inequalities and Tabu Search"
HELENA RAMALHINHO DIAS LOURENÇO, Universitat Pompeu This paper presents an Optimised Search Heuristic that combines a tabu search method with the verification of violated valid inequalities. The solution delivered by the tabu search is partially destroyed by a randomised greedy procedure, and then the valid inequalities are used to guide the reconstruction of a complete solution. An application of the new method to the Job-Shop Scheduling problem is presented. | |||||||||
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Solicitation of Abstracts
This abstracting journal distributes working and accepted papers that use optimization models and methods to handle a wide variety of Operations Research problems, either theoretical or computational. The journal welcomes research with a focus on novel applications and interfaces with operations management, computer science, and Internet and network economics. Topics of interest include, but are not limited to, combinatorial optimization, linear optimization, nonlinear optimization, integer optimization, stochastic optimization, equilibrium and game theory, and techniques for formulating and applying optimization models in practice.
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