http://www.hindawi.com The latest articles from Hindawi Publishing Corporation © 2013 , Hindawi Publishing Corporation . All rights reserved. Mon, 13 May 2013 15:51:17 +0000 http://www.hindawi.com/journals/aor/2013/680539/ We consider two parallel queues, each with independent Poisson arrival rates, that are tended by a single server. The exponential server devotes all of its capacity to the longer of the queues. If both queues are of equal length, the server devotes of its capacity to the first queue and the remaining to the second. We obtain exact integral representations for the joint probability distribution of the number of customers in this two-node network. Then we evaluate this distribution in various asymptotic limits, such as large numbers of customers in either/both of the queues, light traffic where arrivals are infrequent, and heavy traffic where the system is nearly unstable. Charles Knessl and Haishen Yao Copyright © 2013 Charles Knessl and Haishen Yao. All rights reserved. Mon, 15 Apr 2013 13:49:54 +0000 http://www.hindawi.com/journals/aor/2013/279030/ We focus on some convex separable optimization problems, considered by the author in previous papers, for which problems, necessary and sufficient conditions or sufficient conditions have been proved, and convergent algorithms of polynomial computational complexity have been proposed for solving these problems. The concepts of well-posedness of optimization problems in the sense of Tychonov, Hadamard, and in a generalized sense, as well as calmness in the sense of Clarke, are discussed. It is shown that the convex separable optimization problems under consideration are calm in the sense of Clarke. The concept of stability of the set of saddle points of the Lagrangian in the sense of Gol'shtein is also discussed, and it is shown that this set is not stable for the “classical” Lagrangian. However, it turns out that despite this instability, due to the specificity of the approach, suggested by the author for solving problems under consideration, it is not necessary to use modified Lagrangians but only the “classical” Lagrangians. Also, a primal-dual analysis for problems under consideration in view of methods for solving them is presented. Stefan M. Stefanov Copyright © 2013 Stefan M. Stefanov. All rights reserved. Wed, 13 Feb 2013 09:54:56 +0000 http://www.hindawi.com/journals/aor/2013/584762/ This paper presents the use and validation of a generalized learning curve in the economies of scale purchasing experience. The model, based on Wright’s curve, incorporates two extra degrees of freedom to accommodate initial purchases of multiple (instead of single) units and a finite asymptotic price at high volumes. The study shows that each time the part purchase quantity is doubled, the price is reduced either by a constant percentage (a learning rate) or by an approach to an asymptotic plateau rate indicating a point of diminishing returns. Supplier price quotations at multiple purchase quantities were obtained for a pool of 17 critical parts. The data were fitted with the generalized learning curve by the method of least squares regression. The regressed learning rate, first unit price, and the asymptotic price can be used to infer supplier pricing strategies. Coupled with a “should-cost” analysis based on estimates of standard time and material, a system cost reduction task was carried out by the supply chain organization. Lam F. Wong Copyright © 2013 Lam F. Wong. All rights reserved. Sun, 10 Feb 2013 16:16:59 +0000 http://www.hindawi.com/journals/aor/2013/127497/ An Integrated Logistic Support (ILS) service has the objective of improving a system’s efficiency and availability for the life cycle. The system constructor offers the service to the customer, and she becomes the Contractor Logistic Support (CLS). The aim of this paper is to propose an approach to support the CLS in the budget formulation. Specific goals of the model are the provision of the annual cost of ILS activities through a specific cost model and a comprehensive examination of expected benefits, costs and savings under alternative ILS strategies. A simple example derived from an industrial application is also provided to illustrate the idea. Scientific literature is lacking in the topic and documents from the military are just dealing with the issue of performance measurement. Moreover, they are obviously focused on the customer’s perspective. Other scientific papers are general and focused only on maintenance or life cycle management. The model developed in this paper approaches the problem from the perspective of the CLS, and it is specifically tailored on the main issues of an ILS service. M. Elena Nenni Copyright © 2013 M. Elena Nenni. All rights reserved. Thu, 31 Jan 2013 08:10:58 +0000 http://www.hindawi.com/journals/aor/2013/513918/ In the survey of the continuous nonlinear resource allocation problem, Patriksson pointed out that Newton-type algorithms have not been proposed for solving the problem of search theory in the theoretical perspective. In this paper, we propose a Newton-type algorithm to solve the problem. We prove that the proposed algorithm has global and superlinear convergence. Some numerical results indicate that the proposed algorithm is promising. Liping Zhang Copyright © 2013 Liping Zhang. All rights reserved. Mon, 17 Dec 2012 08:29:16 +0000 http://www.hindawi.com/journals/aor/2012/279181/ Most of the real-life decision-making problems have more than one conflicting and incommensurable objective functions. In this paper, we present a multiobjective two-stage stochastic linear programming problem considering some parameters of the linear constraints as interval type discrete random variables with known probability distribution. Randomness of the discrete intervals are considered for the model parameters. Further, the concepts of best optimum and worst optimum solution are analyzed in two-stage stochastic programming. To solve the stated problem, first we remove the randomness of the problem and formulate an equivalent deterministic linear programming model with multiobjective interval coefficients. Then the deterministic multiobjective model is solved using weighting method, where we apply the solution procedure of interval linear programming technique. We obtain the upper and lower bound of the objective function as the best and the worst value, respectively. It highlights the possible risk involved in the decision-making tool. A numerical example is presented to demonstrate the proposed solution procedure. S. K. Barik, M. P. Biswal, and D. Chakravarty Copyright © 2012 S. K. Barik et al. All rights reserved. Mon, 12 Nov 2012 13:55:52 +0000 http://www.hindawi.com/journals/aor/2012/321471/ The main objective of this paper is to develop a two-warehouse inventory model with partial backordering and Weibull distribution deterioration. We consider inflation and apply the discounted cash flow in problem analysis. The discounted cash flow (DCF) and optimization framework are presented to derive the optimal replenishment policy that minimizes the total present value cost per unit time. When only rented or own warehouse model is considered, the present value of the total relevant cost is higher than the case when two-warehouse is considered. The results have been validated with the help of a numerical example. Sensitivity analysis with respect to various parameters is also performed. From the sensitivity analysis, we show that the total cost of the system is influenced by the deterioration rate, the inflation rate, and the backordering ratio. Neeraj Kumar, S. R. Singh, and Rachna Kumari Copyright © 2012 Neeraj Kumar et al. All rights reserved. Tue, 02 Oct 2012 15:25:39 +0000 http://www.hindawi.com/journals/aor/2012/904797/ The introduction of a hybrid genetic programming method (hGP) in fitting and forecasting of the broadband penetration data is proposed. The hGP uses some well-known diffusion models, such as those of Gompertz, Logistic, and Bass, in the initial population of the solutions in order to accelerate the algorithm. The produced solutions models of the hGP are used in fitting and forecasting the adoption of broadband penetration. We investigate the fitting performance of the hGP, and we use the hGP to forecast the broadband penetration in OECD (Organisation for Economic Co-operation and Development) countries. The results of the optimized diffusion models are compared to those of the hGP-generated models. The comparison indicates that the hGP manages to generate solutions with high-performance statistical indicators. The hGP cooperates with the existing diffusion models, thus allowing multiple approaches to forecasting. The modified algorithm is implemented in the Python programming language, which is fast in execution time, compact, and user friendly. Konstantinos Salpasaranis and Vasilios Stylianakis Copyright © 2012 Konstantinos Salpasaranis and Vasilios Stylianakis. All rights reserved. Tue, 02 Oct 2012 13:44:01 +0000 http://www.hindawi.com/journals/aor/2012/175176/ The concept of -convex function and its generalizations is studied with differentiability assumption. Generalized differentiable -convexity and generalized differentiable -invexity are used to derive the existence of optimal solution of a general optimization problem. S. Jaiswal and G. Panda Copyright © 2012 S. Jaiswal and G. Panda. All rights reserved. Thu, 13 Sep 2012 11:02:15 +0000 http://www.hindawi.com/journals/aor/2012/925915/ Abdellah Bnouhachem and Min Li Copyright © 2012 Abdellah Bnouhachem and Min Li. All rights reserved. Thu, 06 Sep 2012 10:20:11 +0000 http://www.hindawi.com/journals/aor/2012/748597/ We mainly study the 𝐶max problem of scheduling n groups of jobs on n special-purpose processors and m general-purpose processors at different speeds provided that the setup time of each job is less than 𝛼 times of its processing time. We first propose an improved LS algorithm. Then, by applying this new algorithm, we obtain two bounds for the ratio of the approximate solution 𝑇LS to the optimal solution T* under two different conditions. Wei Ding Copyright © 2012 Wei Ding. All rights reserved. Mon, 03 Sep 2012 15:25:59 +0000 http://www.hindawi.com/journals/aor/2012/393890/ This paper presents a novel application of operations research to support decision making in blood distribution management. The rapid and dynamic increasing demand, criticality of the product, storage, handling, and distribution requirements, and the different geographical locations of hospitals and medical centers have made blood distribution a complex and important problem. In this study, a real blood distribution problem containing 24 hospitals was tackled by the authors, and an exact approach was presented. The objective of the problem is to distribute blood and its products among hospitals and medical centers such that the total waiting time of those requiring the product is minimized. Following the exact solution, a hybrid heuristic algorithm is proposed. Computational experiments showed the optimal solutions could be obtained for medium size instances, while for larger instances the proposed hybrid heuristic is very competitive. Amir Salehipour and Mohammad Mehdi Sepehri Copyright © 2012 Amir Salehipour and Mohammad Mehdi Sepehri. All rights reserved. Mon, 13 Aug 2012 12:56:28 +0000 http://www.hindawi.com/journals/aor/2012/357954/ Let S be a closed convex set of matrices and C be a given matrix. The matrix nearness problem considered in this paper is to find a matrix X in the set S at which max {|𝑥𝑖𝑗−𝑐𝑖𝑗|} reaches its minimum value. In order to solve the matrix nearness problem, the problem is reformulated to a min-max problem firstly, then the relationship between the min-max problem and a monotone linear variational inequality (LVI) is built. Since the matrix in the LVI problem has a special structure, a projection and contraction method is suggested to solve this LVI problem. Moreover, some implementing details of the method are presented in this paper. Finally, preliminary numerical results are reported, which show that this simple algorithm is promising for this matrix nearness problem. M. H. Xu and H. Shao Copyright © 2012 M. H. Xu and H. Shao. All rights reserved. Tue, 31 Jul 2012 10:19:42 +0000 http://www.hindawi.com/journals/aor/2012/574710/ Deriving the weights of criteria from the pairwise comparison matrix with fuzzy elements is investigated. In the proposed method we first convert each element of the fuzzy comparison matrix into the nearest weighted interval approximation one. Then by using the goal programming method we derive the weights of criteria. The presented method is able to find weights of fuzzy pairwise comparison matrices in any form. We compare the results of the presented method with some of the existing methods. The approach is illustrated by some numerical examples. Mohammad Izadikhah Copyright © 2012 Mohammad Izadikhah. All rights reserved. Tue, 24 Jul 2012 13:22:28 +0000 http://www.hindawi.com/journals/aor/2012/483479/ This paper presents modified halfspace-relaxation projection (HRP) methods for solving the split feasibility problem (SFP). Incorporating with the techniques of identifying the optimal step length with positive lower bounds, the new methods improve the efficiencies of the HRP method (Qu and Xiu (2008)). Some numerical results are reported to verify the computational preference. Min Li Copyright © 2012 Min Li. All rights reserved. Thu, 19 Jul 2012 15:33:39 +0000 http://www.hindawi.com/journals/aor/2012/843486/ We study the existence and the algorithmic aspect of a System of Generalized Mixed Equilibrium Problems involving variational-like inequalities (SGMEPs) in the setting of Banach spaces. The approach adopted is based on the auxiliary principle technique and arguments from generalized convexity. A new existence theorem for the auxiliary problem is established; this leads us to generate an algorithm which converges strongly to a solution of (SGMEP) under weaker assumptions. When the study is reduced to the setting of reflexive Banach spaces, then it can be more relaxed by dropping the coercivity condition. The results obtained in this paper are new and improve some recent studies in this field. H. Mahdioui and O. Chadli Copyright © 2012 H. Mahdioui and O. Chadli. All rights reserved. Wed, 18 Jul 2012 10:48:11 +0000 http://www.hindawi.com/journals/aor/2012/279215/ A new class of generalized functions (𝑑-𝜌-𝜂-𝜃)-type I univex is introduced for a nonsmooth multiobjective programming problem. Based upon these generalized functions, sufficient optimality conditions are established. Weak, strong, converse, and strict converse duality theorems are also derived for Mond-Weir-type multiobjective dual program. Pallavi Kharbanda, Divya Agarwal, and Deepa Sinha Copyright © 2012 Pallavi Kharbanda et al. All rights reserved. Tue, 10 Jul 2012 15:24:45 +0000 http://www.hindawi.com/journals/aor/2012/270910/ Demand unconstraining is one of the key techniques to the success of revenue management systems. This paper surveys the history of research on unconstraining methods and reviews over 130 references including the latest research works in the area. We discuss the relationship between censored data unconstraining and forecasting and review five alternative unconstraining approaches. These methods consider data unconstraining in various situations such as single-class, multi-class, and multi-flight. The paper also proposes some future research questions to bridge the gap between theory and applications. Peng Guo, Baichun Xiao, and Jun Li Copyright © 2012 Peng Guo et al. All rights reserved. Mon, 28 May 2012 09:08:58 +0000 http://www.hindawi.com/journals/aor/2012/543215/ M. Bouznif and R. Giroudeau Copyright © 2012 M. Bouznif and R. Giroudeau. All rights reserved. Wed, 23 May 2012 16:28:26 +0000 http://www.hindawi.com/journals/aor/2012/490983/ An adaptive control of a reverse logistic inventory system with unknown deterioration and disposal rates is considered. An adaptive control approach with a feedback is applied to track the inventory levels toward their goal levels. Also, the updating rules of both deterioration and disposal rates are derived from the conditions of asymptotic stability of the reference model. Important characteristics of the adaptive inventory system are discussed. The adaptive controlled system is modeled by a nonlinear system of differential equations. Finally, the numerical solution of the controlled system is discussed and displayed graphically. Ahmad Alshamrani Copyright © 2012 Ahmad Alshamrani. All rights reserved. Mon, 21 May 2012 10:17:41 +0000 http://www.hindawi.com/journals/aor/2012/768929/ This paper is concerned with the problem of finding the optimal production schedule for an inventory model with time-varying demand and deteriorating items over a finite planning horizon. This problem is formulated as a mixed-integer nonlinear program with one integer variable. The optimal schedule is shown to exist uniquely under some technical conditions. It is also shown that the objective function of the nonlinear obtained from fixing the integrality constraint is convex as a function of the integer variable. This in turn leads to a simple procedure for finding the optimal production plan. Lakdere Benkherouf and Dalal Boushehri Copyright © 2012 Lakdere Benkherouf and Dalal Boushehri. All rights reserved. Sun, 06 May 2012 14:23:47 +0000 http://www.hindawi.com/journals/aor/2012/346358/ We study the cutting and packing (C&P) problems in two dimensions by using phi-functions. Our phi-functions describe the layout of given objects; they allow us to construct a mathematical model in which C&P problems become constrained optimization problems. Here we define (for the first time) a complete class of basic phi-functions which allow us to derive phi-functions for all 2D objects that are formed by linear segments and circular arcs. Our phi-functions support translations and rotations of objects. In order to deal with restrictions on minimal or maximal distances between objects, we also propose adjusted phi-functions. Our phi-functions are expressed by simple linear and quadratic formulas without radicals. The use of radical-free phi-functions allows us to increase efficiency of optimization algorithms. We include several model examples. N. Chernov, Yu. Stoyan, T. Romanova, and A. Pankratov Copyright © 2012 N. Chernov et al. All rights reserved. Mon, 30 Apr 2012 09:08:25 +0000 http://www.hindawi.com/journals/aor/2012/385371/ In today’s competitive markets, selling price and purchasing cost are usually fluctuating with economic conditions. Both selling price and purchasing cost are vital to the profitability of a firm. Therefore, in this paper, I extend the inventory model introduced by Teng and Yang (2004) to allow for not only the selling price but also the purchasing cost to change from one replenishment cycle to another during a finite time horizon. The objective is to find the optimal replenishment schedule and pricing policy to obtain the profit as maximum as possible. The conditions that lead to a maximizing solution guarantee that the existence, uniqueness, and global optimality are proposed. An efficient solution procedure and some theoretical results are presented. Finally, numerical examples for illustration and sensitivity analysis for managerial decision making are also performed. Hui-Ling Yang Copyright © 2012 Hui-Ling Yang. All rights reserved. Thu, 12 Apr 2012 13:24:26 +0000 http://www.hindawi.com/journals/aor/2012/281396/ The problems studied are the separable variational inequalities with linearly coupling constraints. Some existing decomposition methods are very problem specific, and the computation load is quite costly. Combining the ideas of proximal point algorithm (PPA) and augmented Lagrangian method (ALM), we propose an asymmetric proximal decomposition method (AsPDM) to solve a wide variety separable problems. By adding an auxiliary quadratic term to the general Lagrangian function, our method can take advantage of the separable feature. We also present an inexact version of AsPDM to reduce the computation load of each iteration. In the computation process, the inexact version only uses the function values. Moreover, the inexact criterion and the step size can be implemented in parallel. The convergence of the proposed method is proved, and numerical experiments are employed to show the advantage of AsPDM. Xiaoling Fu, Xiangfeng Wang, Haiyan Wang, and Ying Zhai Copyright © 2012 Xiaoling Fu et al. All rights reserved. Thu, 08 Mar 2012 13:02:07 +0000 http://www.hindawi.com/journals/aor/2012/548493/ Operating room scheduling is an important operational problem in most hospitals. In this paper, a novel mixed integer programming (MIP) model is presented for minimizing Cmax and operating room idle times in hospitals. Using this model, we can determine the allocation of resources including operating rooms, surgeons, and assistant surgeons to surgeries, moreover the sequence of surgeries within operating rooms and the start time of them. The main features of the model will include the chronologic curriculum plan for training residents and the real-life constraints to be observed in teaching hospitals. The proposed model is evaluated against some real-life problems, by comparing the schedule obtained from the model and the one currently developed by the hospital staff. Numerical results indicate the efficiency of the proposed model compared to the real-life hospital scheduling, and the gap evaluations for the instances show that the results are generally satisfactory. Somayeh Ghazalbash, Mohammad Mehdi Sepehri, Pejman Shadpour, and Arezoo Atighehchian Copyright © 2012 Somayeh Ghazalbash et al. All rights reserved. Wed, 07 Mar 2012 12:47:56 +0000 http://www.hindawi.com/journals/aor/2012/635282/ We present a solution procedure for a quadratic programming problem with some probabilistic constraints where the model parameters are either triangular fuzzy number or trapezoidal fuzzy number. Randomness and fuzziness are present in some real-life situations, so it makes perfect sense to address decision making problem by using some specified random variables and fuzzy numbers. In the present paper, randomness is characterized by Weibull random variables and fuzziness is characterized by triangular and trapezoidal fuzzy number. A defuzzification method has been introduced for finding the crisp values of the fuzzy numbers using the proportional probability density function associated with the membership functions of these fuzzy numbers. An equivalent deterministic crisp model has been established in order to solve the proposed model. Finally, a numerical example is presented to illustrate the solution procedure. S. K. Barik and M. P. Biswal Copyright © 2012 S. K. Barik and M. P. Biswal. All rights reserved. Mon, 13 Feb 2012 16:08:41 +0000 http://www.hindawi.com/journals/aor/2012/956498/ The performance of a genetic algorithm is dependent on the genetic operators, in general, and on the type of crossover operator, in particular. The population diversity is usually used as the performance measure for the premature convergence. In this paper, a fuzzy genetic algorithm is proposed for solving binary encoded combinatorial optimization problems. A new crossover operator and probability selection technique is proposed based on the population diversity using a fuzzy logic controller. The measurement of the population diversity is based on the genotype and phenotype properties. In this fuzzy inference system, the selection of the crossover operator and its probability are controlled by a set of fuzzy rules derived from the fuzzy logic controller. Extensive computational experiments are conducted on the proposed algorithm, and the results are compared with some crossover operators commonly used for solving multidimensional 0/1 knapsack problems published in the literature. The results indicate that the proposed algorithm is effective in finding better quality solutions. Mohammad Jalali Varnamkhasti, Lai Soon Lee, Mohd Rizam Abu Bakar, and Wah June Leong Copyright © 2012 Mohammad Jalali Varnamkhasti et al. All rights reserved. Wed, 18 Jan 2012 10:21:30 +0000 http://www.hindawi.com/journals/aor/2012/648070/ We introduce the notion of relaxed (ρ-θ)-η-invariant pseudomonotone mappings, which is weaker than invariant pseudomonotone maps. Using the KKM technique, we establish the existence of solutions for variational-like inequality problems with relaxed (ρ-θ)-η-invariant pseudomonotone mappings in reflexive Banach spaces. We also introduce the concept of (ρ-θ)-pseudomonotonicity for bifunctions, and we consider some examples to show that (ρ-θ)-pseudomonotonicity generalizes both monotonicity and strong pseudomonotonicity. The existence of solution for equilibrium problem with (ρ-θ)-pseudomonotone mappings in reflexive Banach spaces are demonstrated by using the KKM technique. N. K. Mahato and C. Nahak Copyright © 2012 N. K. Mahato and C. Nahak. All rights reserved. Tue, 27 Dec 2011 11:34:15 +0000 http://www.hindawi.com/journals/aor/2012/126254/ Globalization, product proliferation, and fast product innovation have significantly increased the complexities of supply chains in many industries. One of the most important advancements of supply chain management in recent years is the development of models and methodologies for controlling inventory in general supply networks under uncertainty and their widefspread applications to industry. These developments are based on three generic methods: the queueing-inventory method, the lead-time demand method and the flow-unit method. In this paper, we compare and contrast these methods by discussing their strengths and weaknesses, their differences and connections, and showing how to apply them systematically to characterize and evaluate various supply networks with different supply processes, inventory policies, and demand processes. Our objective is to forge links among research strands on different methods and various network topologies so as to develop unified methodologies. David Simchi-Levi and Yao Zhao Copyright © 2012 David Simchi-Levi and Yao Zhao. All rights reserved. Tue, 22 Nov 2011 09:39:24 +0000 http://www.hindawi.com/journals/aor/2011/154516/ The selection of the computer language to adopt is usually driven by intuition and expertise, since it is very diffcult to compare languages taking into account all their characteristics. In this paper, we analyze the effciency of programming languages through Data Envelopment Analysis. We collected the input data from The Computer Language Benchmarks Game: we consider a large set of languages in terms of computational time, memory usage, and source code size. Various benchmark problems are tackled. We analyze the results first of all considering programming languages individually. Then, we evaluate families of them sharing some characteristics, for example, being compiled or interpreted. Andrea Ellero and Paola Pellegrini Copyright © 2011 Andrea Ellero and Paola Pellegrini. All rights reserved.