16,249 research outputs found
Models, algorithms, and heuristics for multiobjective commercial territory design
In general, distribution ïŹrms have complex product distribution networks which are formed by thousands of sales points. In this kind of industry there are many interesting problems from the logistic point of view that can appear in different stages of the decision process.
For instance, when a ïŹrm is starting, a ïŹrst problem could be the facility location: where to install the warehouses and/or distribution centers. After that, in order to provide efïŹcient service and to reduce total costs (i.e., production, stock and distribution costs) some questions such as how many products need to be produced, and how to deliver the products to
the ïŹnal customer, need to be answered
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Optimization models and methods for transportation services
Managing transportation services efficiently is essential to both public and private sectors. This dissertation addresses three scheduling problems in modern transportation systems: the network design problem, the train dispatching problem, and the service route design problem. The transportation network design problem with service requirements designs arcs on a directed network and route commodities on the designed arcs so that i) commodities satisfy service requirements and ii) the total cost is minimized. We develop three mathematical programming models: a compact but weak arc-flow formulation, a large but strong path-flow formulation, and a hybrid formulation that uses both the arc-flow and the path-flow representations. We show that the hybrid formulation can significantly strengthen the LP formulation without introducing many variables. To find a good hybrid formulation, we develop columnization and decolumnization algorithms that uses the LP relaxation information to identify commodities that should use the path-flow representation. We also develop valid inequalities for commodities using the path-flow representation. The train dispatching problem schedules the movements of trains on scarce railroad tracks so as to improve the average velocity of trains. We develop a mathematical programming model and strengthen the model using valid inequalities. Besides, we present a heuristic to find a feasible solution quickly, which can serve as the warm-start solution to the MIP solver. For the third problem, we seek to design vehicle routes to deliver and pickup orders for a major grocery chain. We design a GRASP that can incorporate various operational requirements, including warehouse loading capacity, loading sequence, time window requirements, truck volume and weight capacities, and driver time limits. Our GRASP procedure consists of two phases: the solution construction (Phase I) and the Tabu search (Phase II). We show that the neighborhood structure of solutions is highly degenerate, which limits the solution space explored by the Tabu search. We apply the Tabu search with random variable neighborhood to increase the solution space explored.Operations Research and Industrial Engineerin
Embotelladoras ARCA Uses Operations Research to Improve Territory Design Plans
Embotelladoras ARCA was formed in 2001 by integrating three of the oldest bottlers in Mexico and became the second largest bottler of Coca-Cola products in Latin America. The company distributes its products in the northern region of Mexico and, since 2008, in the north of Argentina and Ecuador. The company have soft-drink sales of more than 1.2 billion unit cases and ranks as the third-largest Coca-Cola bottler in the world. The large size of the market and the relevance of a number of problems faced by the company motivate the use and application of operations research models and techniques One of the most relevant problems the company faces is that of how to segment or partition their customers into clusters or territories to accomodate for a better handling of marketing and distribution decisions. This territory design is not entirely arbitrary since it must satisfy several planning requirements such as territory compactness, territory connectivity, territory balancing, and similarity with existing design. Before 2009, these units were defined by âexperienceâ without quantitative tools giving more weight to the territory compactness criterion. This led to a number of undesirable issues such as highly unbalanced territories, that is, the plans ended up with a large disparity in size with respect to both number of customers and total product sales. This imbalance had a negative effect among company workers since each territory (customer order capturing by sales associates, product routing by truck drivers, and so on) is handled by a different team. In this paper, we apply operations research methods to determine better configurations of the territorial units to ensure that each formed territory is relatively similar in size with respect to both number of customers and total product sales while ensuring some other important planning requirements and maximizing territory compactness. The usage of this methodology has resulted in many important benefits for the company, in particular, it has had a significant improvement with respect to the territory imbalances improving from 30 to 5 %. We highlight some other side benefits resulting from this approach. The company has adopted this proposed tool to make their territory design decisions
IR theory, historical materialism, and the false promise of international historical sociology
The three-decades old call for an inter-disciplinary rapprochement between IR Theory and Historical Sociology, starting in the context of the post-positivist debate in the 1980s, has generated a proliferating repertory of contending paradigms within the field of IR, including Neo-Weberian, Post-Structuralist, and Constructivist approaches. Within the Marxist literature, this project comprises an equally rich and diverse set of theoretical traditions, including World-Systems Theory, Neo-Gramscian IR/IPE, the Amsterdam School, Political Marxism, Neo-Leninism, and Postcolonial Theory. More recently, a âthird waveâ of approaches has been announced from within the field of IR, suggesting to move the dialogue from inter-disciplinarity towards an integrated super-discipline of International Historical Sociology (IHS). This proposition has been most persistently advanced by advocates of the theory of Uneven and Combined Development (UCD), claiming to constitute a universal, unitary and sociological theory of IR. This article charts the intellectual trajectory of this ongoing IR/HS dialogue. It moves from a critique of Neo-Weberianism to a critique of UCD against the background of the original promise of the turn in IR to Historical Sociology: the supersession of the prevailing rationalism, structuralism, and positivism in extant mainstream IR approaches through the mobilization of alternative and non-positivistic traditions in the social sciences. This critique will be performed by setting UCD in dialogue with Political Marxism. By anchoring both approaches at opposite ends on the spectrum of Marxist conceptions of social science â respectively the scientistic and the historicist - the argument is that UCD reneges on the promise of Historical Sociology for IR by re-aligning, first by default and now by design, with the meta-theoretical premises of Neo-Realism. This is most visibly expressed in the articulation of a deductive-nomological covering law, leading towards acute conceptual and ontological anachronisms, premised on the radical de-historicisation of the fields of ontology, conceptuality and disciplinarity. This includes the semantic neutering and hyper-abstract re-articulation of the very category, which in IRâs self-perception lends legitimacy to its claim of disciplinary distinctiveness: the international. The article concludes by suggesting that an understanding of Marxism as a historicist social science subverts all calls for the construction of grand theories and, a fortiori, a unitary super-discipline of IHS, premised on a set of universal, space-time indifferent, and abstract categories that hold across the spectrum of world history. In contrast, recovering the historicist credentials of Marxism demands a constant temporalisation and specification of the fields of ontology, agency, conceptuality and disciplinarity. The objective is to lay the foundations for a historicist social science of geopolitics
A GRASP-Tabu Heuristic Approach to Territory Design for Pickup and Delivery Operations for Large-Scale Instances
Weaddressalogisticsdistrictingproblemfacedbyaparcelcompanywhoseoperationsconsistofpickingupanddeliveringpackages overaserviceregion.Thedistrictingprocessaimstofindapartitionoftheserviceregionintodeliveryandcollectionzonesthat may be served by a single vehicle that departs from a central depot. Criteria to be optimized are to balance workload content among the districts and to create districts of compact shape. A solution approach based on a hybrid procedure that combines elements of GRASP and Tabu Search (TS) is proposed to solve large-scale instances. Numerical experimentation is performed consideringdifferentinstancesizesandtypes.Resultsshowthattheproposedsolutionapproachisabletosolvelarge-scaleinstances inreasonablecomputationaltimeswithgoodqualityofthesolutionsobtained.Todeterminethequalityofthesolutions,resultsare comparedwithCPLEXsolutionsandwiththecurrentrealsolutiontohighlightthebenefitsoftheproposedapproach.Conclusions andrecommendationsforfurtherresearchareprovided
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