Browsing by Subject "Heuristics"
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Item Open Access A dynamic multi-level iterative algorithm for clearing European electricity day-ahead markets: an application to the Turkish market(Taylor and Francis Ltd., 2023-05-12) Büke, B.; Sayın, M.; Tanrısever, FehmiDesigning and clearing day-ahead electricity market auctions have recently received significant attention from academia and practice alike. Given the size and the complexity of day-ahead market auctions, clearing them within the time limits imposed by the market is a major practical concern. In this paper, we model all the practical details of the Turkish day-ahead electricity market and provide a new multi-level iterative heuristic to clear the market. We compare our results with a commercial solver using data provided by Energy Exchange Istanbul. Our heuristic achieves an average optimality gap less than 0.09%, with an average solution time of just 14 s; whereas the commercial solver takes, on average, 18 min (and in some cases up to three hours) to find the optimal solution. We also demonstrate that using our heuristic solution to warm-start the commercial solver further reduces the solution time by 25%, on average. Overall, our heuristic proves to be very efficient in clearing the Turkish day-ahead market. We also test the performance of our algorithm as the problem size grows.Item Open Access Analytical loading models in flexible manufacturing systems(Elsevier, 1993) Kırkavak, N.; Dinçer, C.It would be difficult to efficiently implement a manufacturing system without solving its design and operational problems. Based on this framework, a system configuration and tooling problem is modeled. The model turns out to be a large mixed integer linear program, so that some alternative optimal seeking and heuristic techniques are used to solve the model for constructing a flow line structured Flexible Manufacturing System. As a result, it may be possible to construct flexible, efficient, simple and easily controllable manufacturing systems. © 1993.Item Open Access Application mapping algorithms for mesh-based network-on-chip architectures(Springer New York LLC, 2015-03) Tosun, S.; Ozturk, O.; Ozkan, E.; Ozen, M.Due to shrinking technology sizes, more and more processing elements and memory blocks are being integrated on a single die. However, traditional communication infrastructures (e.g., bus or point-to-point) cannot handle the synchronization problems of these large systems. Using network-on-chip (NoC) is a step towards solving this communication problem. Energy- and communication-efficient application mapping is a previously studied problem for mesh-based NoC architectures; however, there is still need for intelligent mapping algorithms since current algorithms either take too much running time or do not determine accurate results. To fill this need, in this study, we propose two mapping algorithms (one based on simulated annealing and one based on genetic algorithm) for energy- and communication-aware mapping problems of mesh-based NoC architectures. We compare these two algorithms with an integer linear programming-based method and a heuristic method using several multimedia and synthetic benchmarks.Item Open Access Arguing to defeat: eristic argumentation and irrationality in resolving moral concerns(Springer, 2020) Kurdoğlu, Rasim Serdar; Ateş, N. Y.By synthesizing the argumentation theory of new rhetoric with research on heuristics and motivated reasoning, we develop a conceptual view of argumentation based on reasoning motivations that sheds new light on the morality of decision-making. Accordingly, we propose that reasoning in eristic argumentation is motivated by psychological (e.g., anxiety reduction) or material (e.g., vested interests) gains that do not depend on resolving the problem in question truthfully. Contrary to heuristic argumentation, in which disputants genuinely argue to reach a practically rational solution, eristic argumentation aims to defeat the counterparty rather than seeking a reasonable solution. Eristic argumentation is susceptible to arbitrariness and power abuses; therefore, it is inappropriate for making moral judgments with the exception of judgments concerning moral taboos, which are closed to argumentation by their nature. Eristic argumentation is also problematic for strategic and entrepreneurial decision-making because it impedes the search for the right heuristic under uncertainty as an ecologically rational choice. However, our theoretical view emphasizes that under extreme uncertainty, where heuristic solutions are as fallible as any guesses, pretense reasoning by eristic argumentation may be instrumental for its adaptive benefts. Expanding the concept of eristic argumentation based on reasoning motivations opens a new path for studying the psychology of reasoning in connection to morality and decision-making under uncertainty. We discuss the implications of our theoretical view to relevant research streams, including ethical, strategic and entrepreneurial decision-making.Item Open Access Bicriteria multiresource generalized assignment problem(John Wiley & Sons, 2014) Karsu, O.; Azizoglu, M.In this study,we consider a bicriteria multiresource generalized assignment problem. Our criteria are the total assignment load and maximum assignment load over all agents. We aim to generate all nondominated objective vectors and the corresponding efficient solutions. We propose several lower and upper bounds and use them in our optimization and heuristic algorithms. The computational results have shown the satisfactory behaviors of our approaches.Item Open Access CCİ Ankara için talep toplama sistemi tasarımı(TMMOB Makina Mühendisleri Odası, 2010) Anasoy, Şeyma; Kara, Semiha; Koçer, Oğuz; Taşkın, Gülce Simge; Yılmaz, Eren; Kara, Bahar Yetiş; Taysı, Tansel; Kökten, SimgeCCİ Satış ile müşteriler arasında bir arayüz oluşturan ön satış elemanları sabah ve akşam ofise gelmektedir. Harcanan bu zaman müşteri ilişkilerinin azalmasına, dolayısıyla CCİ’nin satış sistemindeki verimliliğinin azalmasına sebep olmaktadır. Ayrıca araç yakıt ve ofis giderlerini arttırmakta, ön satış elemanlarının yaşam kalitesini olumsuz yönde etkilemektedir. Bu projenin amacı, CCİ Ankara için yeni bir “Talep Toplama Sistemi” oluşturmaktır. Sistem, ön satış elemanlarının günlük iş akış süreçlerini yenilemiş ve talep toplama ağını yeniden oluşturmuştur. Ayrıca ön satış elemanlarının motivasyonlarının artırılması amacıyla yıllık aktivite plan takvimi düzenlenmiştir. Firmaya önerilen sistem şu an uygulanmakta olup yapılan analizler sonucunda giderlerde ofiste ortalama %30, araçta %12, personel servislerinde ise %60 oranında azalma olduğu saptanmıştır. Ön satış elemanlarının sayısı 84’ten 76’ya düşürülmüş olup, müşteri başına harcanan zaman artırılmıştır.Item Open Access Climbing depth-bounded discrepancy search for solving hybrid flow shop problems(Inderscience Publishers, 2007) Hmida, A. B.; Huguet, M.-J.; Lopez, P.; Haouari, M.This paper investigates how to adapt some discrepancy-based search methods to solve Hybrid Flow Shop (HFS) problems in which each stage consists of several identical machines operating in parallel. The objective is to determine a schedule that minimises the makespan. We present here an adaptation of the Depth-bounded Discrepancy Search (DDS) method to obtain near-optimal solutions with makespan of high quality. This adaptation for the HFS contains no redundancy for the search tree expansion. To improve the solutions of our HFS problem, we propose a local search method, called Climbing Depth-bounded Discrepancy Search (CDDS), which is a hybridisation of two existing discrepancy-based methods: DDS and Climbing Discrepancy Search (CDS). CDDS introduces an intensification process around promising solutions. These methods are tested on benchmark problems. Results show that discrepancy methods give promising results and CDDS method gives the best solutions.Item Open Access A comparative study of computational procedures for the resource constrained project scheduling problem(Elsevier, 1994) Oğuz, O.; Bala, H.Performance of two new integer programming based heuristics together with some special purpose algorithms for project scheduling are tested from a computational point of view. The objective of the study is to compare the quality of solutions obtained by using these algorithms and reach conclusions about their relative merits on this specific problem. © 1994.Item Unknown A comparison of fixed and dynamic pricing policies in revenue management(2013) Şen, A.We consider the problem of selling a fixed capacity or inventory of items over a finite selling period. Earlier research has shown that using a properly set fixed price during the selling period is asymptotically optimal as the demand potential and capacity grow large and that dynamic pricing has only a secondary effect on revenues. However, additional revenue improvements through dynamic pricing can be important in practice and need to be further explored. We suggest two simple dynamic heuristics that continuously update prices based on remaining inventory and time in the selling period. The first heuristic is based on approximating the optimal expected revenue function and the second heuristic is based on the solution of the deterministic version of the problem. We show through a numerical study that the revenue impact of using these dynamic pricing heuristics rather than fixed pricing may be substantial. In particular, the first heuristic has a consistent and remarkable performance leading to at most 0.2% gap compared to optimal dynamic pricing. We also show that the benefits of these dynamic pricing heuristics persist under a periodic setting. This is especially true for the first heuristic for which the performance is monotone in the frequency of price changes. We conclude that dynamic pricing should be considered as a more favorable option in practice.Item Open Access Computational aspects of the maximum diversity problem(Elsevier, 1996) Ghosh, J. B.We address two variations of the maximum diversity problem which arises when m elements are to be selected from an n-element population based on inter-element distances. We study problem complexity and propose randomized greedy heuristics. Performance of the heuristics is tested on a limited basis.Item Open Access Constrained min-cut replication for K-way hypergraph partitioning(Institute for Operations Research and the Management Sciences (I N F O R M S), 2014) Yazici V.; Aykanat, CevdetReplication is a widely-used technique in information retrieval and database systems for providing fault tolerance and reducing parallelization and processing costs. Combinatorial models based on hypergraph partitioning are proposed for various problems arising in information retrieval and database systems. We consider the possibility of using vertex replication to improve the quality of hypergraph partitioning. In this study, we focus on the constrained min-cut replication (CMCR) problem, where we are initially given a maximum replication capacity and a K-way hypergraph partition with an initial imbalance ratio. The objective in the CMCR problem is finding the optimal vertex replication sets for each part of the given partition such that the initial cut size of the partition is minimized, where the initial imbalance is either preserved or reduced under the given replication capacity constraint. In this study, we present a complexity analysis of the CMCR problem and propose a model based on a unique blend of coarsening and integer linear programming (ILP) schemes. This coarsening algorithm is derived from a novel utilization of the Dulmage-Mendelsohn decomposition. Experiments show that the ILP formulation coupled with the Dulmage-Mendelsohn decomposition-based coarsening provides high quality results in practical execution times for reducing the cut size of a given K-way hypergraph partition. © 2014 INFORMS.Item Open Access Data dependent worst case bound improving techniques in zero-one programming(Elsevier BV, 1991) Oğuz, OsmanA simple perturbation of data is suggested for use in conjunction with approximation algorithms for the purpose of improving the available bounds (upper and lower), and the worst case bounds. The technique does not require the approximation algorithm (heuristic) to provide a worst case bound to be applicable.Item Open Access Debris removal during disaster response: a case for Turkey(Elsevier, 2016) Sahin, H.; Kara, B. Y.; Karasan, O. E.Debris occurs from the ruin and wreckage of structures during a disaster. Proper removal of debris is of great importance because it blocks roads and prohibits emergency aid teams from accessing disaster-affected regions. Poor disaster management, lack of efficiency and delays in debris removal cause disruptions in providing shelter, nutrition, healthcare and communication services to disaster victims, and more importantly, result in loss of lives. Due to the importance of systematic and efficient debris removal from the perspectives of improving disaster victims quality of life and allowing the transportation of emergency relief materials, the focus of this study is on providing emergency relief supplies to disaster-affected regions as soon as possible by unblocking roads through removing the accumulated debris. We develop a mathematical model for the problem that requires long CPU times for large instances. Since it is crucial to act quickly in an emergency case, we also propose a heuristic methodology that solves instances with an average gap of 1% and optimum ratio of 80.83%.Item Open Access Dynamic lot sizing for a warm/cold process: heuristics and insights(Elsevier, 2013-09) Toy, A. Ö.; Berk, E.We consider the dynamic lot sizing problem for a warm/cold process where the process can be kept warm at a unit variable cost for the next period if more than a prespecified quantity has been produced. Exploiting the optimal production plan structures, we develop nine rule-based forward solution heuristics. Proposed heuristics are modified counterparts of the heuristics developed previously for the classical dynamic lot sizing problem. In a numerical study, we investigate the performance of the proposed heuristics and identify operating environment characteristics where each particular heuristic is the best or among the best. Moreover, for a warm/cold process setting, our numerical studies indicate that, when used on a rolling horizon basis, a heuristic may also perform better costwise than a solution obtained using a dynamic programming approach.Item Open Access The dynamic lot-sizing problem with convex economic production costs and setups(Elsevier, 2014-09) Kian, R.; Gurler, U.; Berk, E.In this work the uncapacitated dynamic lot-sizing problem is considered. Demands are deterministic and production costs consist of convex costs that arise from economic production functions plus set-up costs. We formulate the problem as a mixed integer, non-linear programming problem and obtain structural results which are used to construct a forward dynamic-programming algorithm that obtains the optimal solution in polynomial time. For positive setup costs, the generic approaches are found to be prohibitively time-consuming; therefore we focus on approximate solution methods. The forward DP algorithm is modified via the conjunctive use of three rules for solution generation. Additionally, we propose six heuristics. Two of these are single-stepSilver-Meal and EOQ heuristics for the classical lot-sizing problem. The third is a variant of the Wagner-Whitin algorithm. The remaining three heuristics are two-step hybrids that improve on the initial solutions of the first three by exploiting the structural properties of optimal production subplans. The proposed algorithms are evaluated by an extensive numerical study. The two-step Wagner-Whitin algorithm turns out to be the best heuristic.Item Open Access The effect of economies-of-scale on the performance of lot-sizing heuristics in rolling horizon basis(Taylor & Francis, 2020-02-26) Kian, R.; Berk, Emre; Gürler, Ülkü; Rezazadeh, H.; Yazdani, B.In this article, we consider the production planning problem in the presence of (dis)economies-of-scale in production costs on a rolling horizon basis with a fixed forecast horizon. We propose variants of three well-known and commonly used heuristics (Wagner–Whitin, Silver–Meal and Least Unit Cost) adapted for this particular setting. In an extensive numerical study with demands exhibiting stationary, increasing and decreasing trends and seasonality, we demonstrate that having longer forecast horizon is less effective in obtaining more cost effective production plans when the production cost function is convex and also when fixed setup cost is lower, which both are proxy to lack of economies-of-scale.Item Open Access Effects of ignorance and information on judgments and decisions(Society for Judgment and Decision Making, 2011) Ayton, P.; Önkal D.; McReynolds, L.We compared Turkish and English students’ soccer forecasting for English soccer matches. Although the Turkish students knew very little about English soccer, they selected teams on the basis of familiarity with the team (or its identified city); their prediction success was surprisingly similar to knowledgeable English students—consistent with Goldstein and Gigerenzer’s (1999; 2002) characterization of the recognition heuristic. The Turkish students made forecasts for some of the matches with additional information—the half-time scores. In this and a further study, where British students predicting matches for foreign teams could choose whether or not to use half-time information, we found that predictions that could be made by recognition alone were influenced by the half-time information. We consider the implications of these findings in the context of Goldstein and Gigerenzer’s (2002, p. 82) suggestion that “. . . no other information can reverse the choice determined by recognition” and a recent more qualified statement (Gigerenzer & Goldstein, 2011) indicating that two processes, recognition and evaluation guide the adaptive selection of the recognition heuristic.Item Open Access Evsel atık toplama ağı tasarımı ve geri kazanım süreçlerinin iyileştirilmesi(TMMOB MAKİNA MÜHENDİSLERİ ODASI, 2008) Aydın, Hande; Başoğlu, Deniz; Demirel, Melih; Güleç, Ali; Palağlu, Ekin; Şimşek, Aslı; Yetiş-Kara, BaharMevcut sistemin analizi neticesinde problem evsel atık toplama ve ayrıştırma süreçlerinin yüksek maliyetli olması olarak tanımlanmış ve bu süreçler için maliyetleri azaltacak iyileştirme çalışmaları yapılmıştır. Ayrıca palet atölyesinin önceki yerleşiminin ayrıştırma süreçlerinin verimini olumsuz yönde etkilediği gözlemlendikten sonra firmanın isteğiyle yeni yapılacak palet atölyesi için bir yerleşim planı tasarlanmıştır. Yapılan çalışmalar sonucunda firmaya tüm problemlerin çözümüne yönelik öneriler sunulmuştur. Bu öneriler şu an uygulanmaktadır. Sunulan önerilerin uygulanması neticesinde palet atölyesi için malzemelerin dolaşma mesafelerin ortalama %70 oranında azalması, ayrıştırma bandına eklenen teknolojik donanımlarla ayrıştırılan atık miktarının %17 oranında artması ve tasarımı bizlere ait RotaÇiz programı ile toplam toplama mesafesinin %42 oranında azalması beklenmektedir.Item Open Access An exact approach to minimize single machine total weighted tardiness problem with unequal release dates(Bilkent University, 1998) Özdemir, DenizIn this research, the problem of scheduling a set of jobs on a single machine to minimize total weighted tardiness with unequal release dates is considered. We present a new dominance rule by considering the time depending orderings between each pair of jobs. The proposed rule provides a sufficient condition for local optimality. Therefore, if any sequence violates the dominance rule then switching the violating jobs either lowers the total weighted tardiness or leaves it unchanged. Based on the dominance rule, an algorithm is developed which is compared to a number of heuristics in the literature. Our computational results indicate that the proposed algorithm dominates the competing algorithms in all runs, therefore it can improve the upper bounding scheme and can be used in reducing the number of alternatives in any enumerative algorithm. Furthermore, the proposed dominance rule is incorporated in a branch and bound algorithm in conjunction with lower bounding scheme, branching condition and search strcitegy. To the best of our knowledge, author know of no other published exact approach for l|rj| problem. This enhances contribution of our study in the literature.Item Open Access Match-up scheduling under a machine breakdown(Elsevier, 1999) Aktürk, M. S.; Görgülü, E.When a machine breakdown forces a modified flow shop (MFS) out of the prescribed state, the proposed strategy reschedules part of the initial schedule to match up with the preschedule at some point. The objective is to create a new schedule that is consistent with the other production planning decisions like material flow, tooling and purchasing by utilizing the time critical decision making concept. We propose a new rescheduling strategy and a match-up point determination procedure through a feedback mechanism to increase both the schedule quality and stability. The proposed approach is compared with alternative reactive scheduling methods under different experimental settings. © 1999 Elsevier Science B.V. All rights reserved.