Arild Hoff

• Knudseth, Sunniva Haukvik; Molland, Even; Hoff, Arild; Hvattum, Lars Magnus & Oppen, Johan (2024). Decision support for allocating farmed fish to customer orders using a bi-objective optimization model. Decision Making in Manufacturing and Services. ISSN 1896-8325. 16, p. 67–90. doi: 10.7494/dmms.2022.16.5019. Full text in Research Archive Show summary

  Aquaculture is an important industry in certain coastal areas. Focusing on farming of salmon and trout, an operational planning problem arises with the goal of allocating supply of fish to demand expressed through customer orders. This paper provides a conceptual model of such a planning problem, defines a corresponding bi-objective mathematical programming model. The problem is novel with respect to the structure of the transportation of fish, and the rules for satisfying customer orders with respect to fish size, quality, certification, and health status. Computational experiments are conducted to gain further insights into the use of the provided model to provide support for planners involved in the operational decision making. Results indicate that the bi-objective optimization model can be useful in situations where supply is insufficient to cover all the demand within a given planning horizon.

• Shaabani, Homayoun; Hvattum, Lars Magnus; Laporte, Gilbert & Hoff, Arild (2024). Stability metrics for a maritime inventory routing problem under sailing time uncertainty. EURO Journal on Transportation and Logistics. ISSN 2192-4376. 13. doi: 10.1016/j.ejtl.2024.100146. Full text in Research Archive Show summary

  We study a multi-product maritime inventory routing problem (MIRP) with sailing time uncertainty. We explicitly consider the replanning that happens after uncertainty is revealed. The objective is to determine the stability of the adjusted plans after the occurrence of an uncertain event and to evaluate the effect of incorporating different stability metrics in the rescheduling process. Five stability metrics are introduced, and mathematical formulations of the MIRP incorporating each metric are presented. A reoptimization framework is then used to analyze the impact of each stability metric. Calculations are performed using 360 instances. The main result is that adjustments to the original plan occur at no additional cost almost 50% of the time. If decision makers want a more stable plan, they should accept a 5% cost deterioration, resulting in 20% more stable solutions.

• Shaabani, Homayoun; Hvattum, Lars Magnus; Laporte, Gilbert & Hoff, Arild (2023). A goal programming model for the stability analysis of a maritime inventory routing replanning problem. Maritime Transport Research. 5(December). doi: 10.1016/j.martra.2023.100101. Full text in Research Archive
• Shaabani, Homayoun; Hoff, Arild; Hvattum, Lars Magnus & Laporte, Gilbert (2023). A matheuristic for the multi-product maritime inventory routing problem. Computers & Operations Research. ISSN 0305-0548. 154(June), p. 1–19. doi: 10.1016/j.cor.2023.106214. Full text in Research Archive Show summary

  This paper considers a multi-product maritime inventory routing problem in which the routes of the vessels are determined while inventories in the ports must remain within given bounds. Since there is more than one product, each port can be a consumption port for one product and a production port for another product. We propose a matheuristic to deal with large-size instances with a planning horizon of 60 days. The first phase of the heuristic identifies a subset of the arcs in order to use them as input parameters for the second phase. In the second phase, a mathematical model is solved with the selected arcs fixed. These two phases are iterated until a stopping criterion is satisfied. The solutions produced by the matheuristic are compared with those obtained by CPLEX. Comparing the single-product version of the problem with the multi-product version revealed that instances with multiple products require significantly more run time compared with the single-product instances.

• Bentsen, Håkon; Hoff, Arild & Hvattum, Lars Magnus (2022). Exponential extrapolation memory for tabu search. EURO Journal on Computational Optimization. ISSN 2192-4406. 10. doi: 10.1016/j.ejco.2022.100028. Full text in Research Archive Show summary

  Tabu search is a well-established metaheuristic framework for solving hard combinatorial optimization problems. At its core, the method uses different forms of memory to guide a local search through the solution space so as to identify high-quality local optima while avoiding getting stuck in the vicinity of any particular local optimum. This paper examines characteristics of moves that can be exploited to make good decisions about steps that lead away from recently visited local optima and towards a new local optimum. Our approach uses a new type of adaptive memory based on a construction called exponential extrapolation. The memory operates by means of threshold inequalities that ensure selected moves will not lead to a specified number of most recently encountered local optima. Computational experiments on a set of one hundred different benchmark instances for the binary integer programming problem suggest that exponential extrapolation is a useful type of memory to incorporate into a tabu search. Keywords: 0-1 Integer programming, binary optimization, adaptive memory, tabu search

• Hrabec, Dušan; Hvattum, Lars Magnus & Hoff, Arild (2022). The value of integrated planning for production, inventory, and routing decisions : a systematic review and meta-analysis. International Journal of Production Economics. ISSN 0925-5273. 248(June), p. 1–13. doi: 10.1016/j.ijpe.2022.108468. Full text in Research Archive Show summary

  This paper presents a comparison of sequential and integrated planning for the production routing problem, in which production, inventory, and routing decisions must be made. The aim is to estimate the expected value of treating the problems as a whole, rather than making decisions sequentially. In particular, the following research questions are posed: What is the expected cost reduction when combining production, inventory, and routing in a single modeling framework, compared to solving the problems individually in a sequence? Under which circumstances is it most beneficial to tackle an integrated problem? In other words, the goal is to establish whether the solutions obtained by the integration are clearly better than approximate solutions obtained by a more simplified process, and if so, under which circumstances this difference is the most pronounced. To answer these research questions, a systematic review was performed, resulting in a set of 20 relevant articles that were analyzed in depth. For the first research question, computational results from 15 articles were obtained and analyzed through a meta-analysis. The analysis estimated an expected cost savings provided by integration of 11.08%, with a 95% confidence interval of [6.58%, 15.58%]. For the second research question, individual results obtained via sensitivity analyses in 20 relevant articles were summarized qualitatively, enabling insights into how the potential savings by integration is influenced by parameters such as the degrees of freedom, the cost, and the capacity. Keywords: sequential planning, value of integration, distribution, production routing problem

• Saeed, Naima; Hoff, Arild & Larsen, Odd I (2021). Analysis of hinterland transport strategies when exporting perishable products. Research in Transportation Business and Management (RTBM). ISSN 2210-5395. 43(June), p. 1–9. doi: 10.1016/j.rtbm.2021.100766. Full text in Research Archive Show summary

  Since a good hinterland connection is considered an important factor in port competitiveness, the objective of this paper is to analyse the impact of the development of hinterland transport strategies on the competitiveness of the port by taking the Port of Cape Town, the Republic of South Africa as an example. The development of transport strategies is reflected in terms of a lower cost and higher frequency of inland transport. To investigate the interplay among export products, transport, and access to a port for exporters, we use a linear programming model. The model considers both the choice of transport modes and the impacts of improved inland transport strategies. The model could easily be extended to deal with other modes or transport alternatives. It is assumed that, initially, two modes of transport – trucks and railway − are available for transportation of the export product from the farm to the port. The analysis is extended by including intermodal transportation as a combination of railway and road transport. The results of the analysis show that improving the rail services and offering more frequent rail services from the farm to the port, could lead to a better and more flexible transportation strategy. Keywords: port competitiveness, inland hinterland, dry ports, perishable products, intermodal transport, linear programming

• Mecler, Davi; Abu-Marrul, Victor; Martinelli, Rafael & Hoff, Arild (2021). Iterated greedy algorithms for a complex parallel machine scheduling problem. European Journal of Operational Research. ISSN 0377-2217. 300(2), p. 545–560. doi: 10.1016/j.ejor.2021.08.005. Full text in Research Archive Show summary

  This paper addresses a complex parallel machine scheduling problem with jobs divided into operations and operations grouped in families. Non-anticipatory family setup times are held at the beginning of each batch, defined by the combination of one setup-time and a sequence of operations from a unique family. Other aspects are also considered in the problem, such as release dates for operations and machines, operation’s sizes, and machine’s eligibility and capacity. We consider item availability to define the completion times of the operations within the batches, to minimize the total weighted completion time of jobs. We developed Iterated Greedy (IG) algorithms combining destroy and repair operators with a Random Variable Neighborhood Descent (RVND) local search procedure, using four neighborhood structures to solve the problem. The best algorithm variant outperforms the current literature methods for the problem, in terms of average deviation for the best solutions and computational times, in a known benchmark set of 72 instances. New upper bounds are also provided for some instances within this set. Besides, computational experiments are conducted to evaluate the proposed methods’ performance in a more challenging set of instances introduced in this work. Two IG variants using a greedy repair operator showed superior performance with more than 70% of the best solutions found uniquely by these variants. Despite the simplicity, the method using the most common destruction and repair operators presented the best results in different evaluated criteria, highlighting its potential and applicability in solving a complex machine scheduling problem. Keywords: metaheuristics, machine scheduling, family scheduling, batchingm setup times

• Hrydziushka, Darya; Pasha, Urooj & Hoff, Arild (2021). An extended model for disaster relief operations used on the Hagibis typhoon case in Japan. Logistics. 5(2), p. 1–30. doi: 10.3390/logistics5020039. Full text in Research Archive Show summary

  This paper presents a generalization of a previously defined lexicographical dynamic flow model based on multi-objective optimization for solving the multi-commodity aid distribution problem in the aftermath of a catastrophe. The model considers distribution of the two major commodities of food and medicine, and seven different objectives, and the model can easily be changed to include more commodities in addition to other and different priorities between the objectives. The first level in the model is to maximize the amount of aid distributed under the given constraints. Keeping the optimal result from the first level, the second level can be solved considering objectives such as the cost of the operation, the time of the operation, the equity of distribution for each type of humanitarian aid, the priority of the designated nodes, the minimum arc reliability, and the global reliability of the route. The model is tested on a recent case study based on the Hagibis typhoon disaster in Japan in 2019. The paper presents a solution for the distribution problem and provides a driving schedule for vehicles for delivering the commodities from depots to the regional centers in need for humanitarian aid. Keywords: humanitarian logistics, multicriteria, distribution models

• Husakou, Anatol; Hvattum, Lars Magnus; Danielsen, Ketil & Hoff, Arild (2020). An application of the multi-depot heterogeneous fixed fleet open vehicle routing problem. International Journal of Advanced Operations Management (IJAOM). ISSN 1758-938X. 12(2), p. 142–155. doi: 10.1504/IJAOM.2020.108262. Full text in Research Archive Show summary

  This work describes an application of a multi-depot heterogeneous fixed fleet open vehicle routing problem. A contractor owns a fleet of vehicles with different capacities and running costs. The fleet is used to transport craftsmen from their homes to assigned project sites and back, with some of the craftsmen appointed as drivers while others are passengers. An optimisation model is described that enables the contractor to minimise the transportation costs, and a computational study shows that the model can be solved to optimality for realistically sized instances using a standard mixed-integer programming solver. A variant of the problem is also considered, where the assignment of craftsmen to projects is not fixed a priori. For this variant, several simple heuristic rules are investigated to generate project assignments, and computational results show that they are able to find improved assignments. Keywords: mixed integer programming, assignment, transportation

• Hrabec, Dušan; Senland, Preben; Nevrly, Vlastimir; Popela, Pavel; Hoff, Arild & Šomplák, Radovan [Show all 7 contributors for this article] (2019). Quantity-predictive vehicle routing problem for smart waste collection. Chemical Engineering Transactions. ISSN 1974-9791. 76, p. 1249–1254. doi: 10.3303/CET1976209. Full text in Research Archive Show summary

  The current trends in the field of waste management involves the use of modern technologies such as wireless sensors. The smart waste management with Sensor Technology involves an integration of the so-called smart trash bins and containers into existing network by using sensors that fill level of the bins and containers. Apart from the technological aspects of the problem, this arrangement points to the need of development of new decision-making tools that allow collectors to make fast and smart operative decisions on the waste collection. The sensors from the waste containers read the current fill-height once a day and send the information to the central database. The central decision-maker appraises the data and makes the waste collection plan for an entire (e.g., one week) collection period; note that this improves existing models on the data available and used. The aim of this paper is to present complex modelling ideas, develop a simple mathematical model, discuss its complexity and propose/discuss a computational approach in order to solve the collection problem. The objective is to optimize the dynamic planning on daily garbage-truck schedules with respect to minimization of transportation costs that also reflects a positive environmental impact presented by savings in transportation/routing distance. The secondary objective is to optimally decide on early collection of partly-filled containers, especially those directly on or close to the optimum route linking the full ones considering waste production rates in the next days. The paper outlines some directions for further research such as the need of modifying the old-existing models into a form utilizing the newly available data. This leads to specific vehicle routing problems that request appropriate computational time requirements and the need of suitable heuristic methods development.

• Bach, Terje; Jæger, Bjørn & Hoff, Arild (2018). Production planning and control as routing in manufacturing networks. The MENDEL Soft Computing journal : International Conference on Soft Computing MENDEL. ISSN 1803-3814. 24(2), p. 1–8. doi: 10.13164/mendel.2018.2.001. Full text in Research Archive Show summary

  In this paper, we explore the use of network routing for production planning and control in manufacturing of complex industrial products. Such a product is the result of a joint effort of many manufacturing companies; each considered a collection of work centre nodes connected by transportation links forming a company-wide manufacturing network. Each company is, in turn considered a manufacturing node connected to other manufacturers by transportation links forming a distributed manufacturing network that produces the final product. We model the manufacturing network as a distribution network where the incoming and outgoing inventories of products are distinct nodes in addition to the work centre nodes. Production planning and control are done by minimizing the cost of handling all products in all work centre nodes. This formulation provides a scalable and flexible production planning and control scheme adhering to the networked structure of manufacturing of complex products. We apply the model to a company-wide manufacturing network as a first approach. A case study using the model demonstrates production planning using network routing at a manufacturer of ship propulsion engines. Keywords: discrete manufacturing, next generation manufacturing systems, industry 4.0, advanced manufacturing, smart manufacturing

• Engelseth, Per; Karlsen, Irina; Huang, Shulin & Hoff, Arild (2018). The value aspect of reallocating seafood freight from road to sea transport. In Egilmez, Gokhan (Eds.), Agricultural Value Chain. IntechOpen. ISSN 9781789230079. p. 59–80. doi: 10.5772/intechopen.68779. Full text in Research Archive Show summary

  A case study elaborates on the project organization promoting change of transport mode in a food chain from a value perspective. This project organization may perspectively be viewed as a supply chain with value conceptions different from the everyday seafood supply chain it is meant to develop. Value is in this project context revealed as an intersubjective complex phenomenon, founded in that value conceptions by actors located at different locations in the supply chain. This renders customer value as one of many dynamic value components in this project organization. Value embedded in a supply chain is therefore always a source of uncertainty, a subjective perspective; it cannot be considered as a clear functional purpose in projects aimed at developing food supply. The route to reallocate seafood freight should therefore focus on organizing interconnectivity to support networking and the project members accepting that the project outcome is emergent. Keywords: food logistics, sustainability, short sea shipping, intermodal transport, customer value, supply chain management

• Pasha, Urooj; Hoff, Arild & Hvattum, Lars Magnus (2018). The multi-period fleet size and mix vehicle routing problem with stochastic demands. In Diez, Pedro; Neittaanmäki, Pekka; Periaux, Jacques; Tuovinen, Tero & Bräysy, Olli (Ed.), Computational Methods and Models for Transport. Springer. ISSN 9783319544908. p. 121–146. doi: 10.1007/978-3-319-54490-8_9. Full text in Research Archive Show summary

  The multi-period fleet size and mix vehicle routing problem with stochastic demands is a new optimization problem that arises from the need to make strategic fleet sizing decisions while taking into consideration tactical planning and operational uncertainty. The setting is a distribution company that delivers goods to a set of customers and where the expected demand for different customers vary from period to period. The actual demand in a given period is stochastic, and is only revealed when visiting the customer. The objective is to minimize total expected costs, consisting of vehicle acquisition costs, routing costs, and the expected cost of route failures. Route failures occur when a vehicle arrives at a customer with an insufficient amount of goods, resulting in the need to refill the vehicle at the depot. The problem is formulated as a mixed integer programming problem. A heuristic for solving the problem is described and implemented, and a computational study is conducted on a set of varied test instances. Keywords: tabu search, heuristic, scenario, stochastic programming, recourse 

• Colmenar, J. Manuel; Hoff, Arild; Martí, Rafael & Duarte, Abraham (2018). Scatter search for the bi-criteria p-median p-dispersion problem. Progress in Artificial Intelligence. ISSN 2192-6352. 7(1), p. 31–40. doi: 10.1007/s13748-017-0132-6. Full text in Research Archive Show summary

  The bi-criteria p-median p-dispersion is a challenging optimization problem that belongs to the family of location problems. To our knowledge, no metaheuristic has been proposed to this problem, where a multi-objective approach has to be considered. In this paper, we propose a multi-objective Scatter Search implementation in which three different improvement methods have been analyzed. Our results have been compared with the state of the art obtaining better hypervolume values and promising results in terms of dominance of solutions. Keywords: facility problems, p-median, p-dispersion, scatter search

• Martí, Rafael; Campos, Vicente; Hoff, Arild & Peiró, Juanjo (2018). Heuristics for the min–max arc crossing problem in graphs. Expert Systems With Applications. ISSN 0957-4174. 109(November), p. 100–113. doi: 10.1016/j.eswa.2018.05.008. Full text in Research Archive Show summary

  In this paper, we study the visualization of complex structures in the context of automatic graph drawing. Constructing geometric representations of combinatorial structures, such as networks or graphs, is a difficult task that requires an expert system. The automatic generation of drawings of graphs finds many applications from software engineering to social media. The objective of graph drawing expert systems is to generate layouts that are easy to read and understand. This main objective is achieved by solving several optimization problems. In this paper we focus on the most important one: reducing the number of arc crossings in the graph. This hard optimization problem has been studied extensively in the last decade, proposing many exact and heuristic methods to minimize the total number of arc crossings. However, despite its practical significance, the min–max variant in which the maximum number of crossings over all edges is minimized, has received very little attention. We propose new heuristic methods based on the strategic oscillation methodology to solve this NP-hard optimization problem. Our experimentation shows that the new method compares favorably with the existing ones, implemented in current graph drawing expert systems. Therefore, a direct application of our findings will improve these functionality (i.e., crossing reduction) of drawing systems. Keywords: graph drawing expert system, metaheuristics, crossing reduction, iterated greedy

• Hoff, Arild; Peiró, Juanjo; Corberán, Ángel & Martí, Rafael (2017). Heuristics for the capacitated modular hub location problem. Computers & Operations Research. ISSN 0305-0548. 86(October), p. 94–109. doi: 10.1016/j.cor.2017.05.004. Full text in Research Archive Show summary

  In this paper we study the hub location problem, where the goal is to identify an optimal subset of facilities (hubs) to minimize the transportation cost while satisfying certain capacity constraints. In particular, we target the single assignment version, in which each node in the transportation network is assigned to only one hub to route its traffic. We consider here a realistic variant introduced previously, in which the capacity of edges between hubs is increased in a modular way. This reflects the practical situation in air traffic where the number of flights between two locations implies a capacity in terms of number of passengers. Then, the capacity can be increased in a modular way, as a factor of the number of flights. We propose heuristic methods to obtain high-quality solutions in short computing times. Specifically, we implement memory structures to create advanced search methods and compare them with previous heuristics on a set of benchmark instances. Memory structures have been widely implemented in the context of the tabu search methodology, usually embedded in local search algorithms. In this paper we explore an alternative design in which the constructive method is enhanced with frequency information and the local search is coupled with a path relinking post-processing. Statistical tests confirm the superiority of our proposal with respect to previous developments. Keywords: hub location, modular links, heuristic algorithms, memory structures

• Pasha, Urooj; Hoff, Arild & Hvattum, Lars Magnus (2016). Simple heuristics for the multi-period fleet size and mix vehicle routing problem. INFOR: Information Systems and Operational Research. ISSN 0315-5986. 54(2), p. 97–120. doi: 10.1080/03155986.2016.1149314. Full text in Research Archive Show summary

  Most of the research on vehicle routing problems has focused on the operational or the tactical level. However, any decision made on a strategic level will affect the lower level decisions. One type of strategic decision that has been considered in the literature is to compose an appropriate fleet of different vehicles to perform transportation tasks, which yields the fleet size and mix vehicle routing problem (FSMVRP). This work defines a new variant of the FSMVRP where the customer demands may vary over a set of periods, for example by having different demands on each day of the week. The objective is to find the best fleet composition that can be used to repeatedly fulfil the customer demands, as well as the best routing with that fleet for each of the different periods in the planning horizon. Simple heuristics incorporating a tabu search are implemented to find the fleet composition. Computational results are reported on instances created from a set of standard FSMVRP test instances.

• Pasha, Urooj; Hoff, Arild & Løkketangen, Arne (2014). A hybrid approach for milk collection using trucks and trailers. Annals of Management Science. ISSN 2161-5012. 3(1), p. 85–107. doi: 10.24048/ams3.no1.2014-85. Full text in Research Archive Show summary

  Collection and transportation of milk from farms to production factories is a crucial issue around the world. This problem can often be seen as a special case of the Truck and Trailer Vehicle Routing Problem (TTVRP) in which a trailer cannot be driven along with a truck to the farms and must be parked in the nearest available parking place while the truck visits farms and collects milk. Then, the truck returns to the parking place, transfers milk to the trailer and starts a new sub route or continues the route with the trailer. The collections, transportation, and distribution operations in TINE SA, a leading dairy company in Norway, is a typical example of this problem. In this paper, we solve a real world planning and distribution problem for the company (TINE SA). A method involving a clustering technique followed by a heuristic based on tabu search is developed to solve this problem. The proposed method is able to find a cost-effective solution by using natural geographical clusters and choosing vehicle types that fit better to the farms production and the dairy plants demand. The new suggested solution produces a more suitable vehicle mix and collecting frequency, a better utilization of vehicles and smaller variable costs than the current route structure of the company. Keywords: vehicle routing, tabu search, clustering

• Pasha, Urooj; Hoff, Arild & Løkketangen, Arne (2013). The shrinking and expanding heuristic for the fleet size and mix vehicle routing problem. Komunikácie - vedecké listy Žilinskej univerzity v Žiline. ISSN 1335-4205. 15(1), p. 6–13. Full text in Research Archive Show summary

  The FSMVRP (Fleet Size and Mix Vehicle Routing Problem) is a variant of the classical Capacitated Vehicle Routing Problem, CVRP. We suggest a new methodology, called the Shrinking and Expanding Heuristic (SEH) which is incorporated in a standard tabu search. To determine an appropriate fleet mix is a major challenge in this type of problem and the SEH technique is especially developed to find a good combination of vehicles by introducing a mechanism for changing the existing fleet mix during the search, thus also changing the underlying route structure. The SEH utilizes the concept of depletion and expansion of routes depending upon the filling degree of a vehicle. This strategy is tested on standard problem instances and good quality solutions are obtained. Keywords: Shrinking and expanding heuristics, filling degree, fleet size and mix vehicle routing problem, tabu search.

• Pasha, Urooj; Hoff, Arild & Løkketangen, Arne (2013). The shrinking and expanding heuristic forthe fleet size and mix vehicle routing problem. Komunikácie - vedecké listy Žilinskej univerzity v Žiline. ISSN 1335-4205. 15(1), p. 6–13. Full text in Research Archive
• Andersson, Henrik; Hoff, Arild; Christiansen, Marielle; Hasle, Geir & Løkketangen, Arne (2010). Industrial aspects and literature survey: Combined inventory management and routing. Computers & Operations Research. ISSN 0305-0548. 37(9), p. 1515–1536. doi: 10.1016/j.cor.2009.11.009. Full text in Research Archive Show summary

  This paper describes industrial aspects of combined inventory management and routing in maritime and road-based transportation, and gives a classification and comprehensive literature review of the current state of the research. The literature is contrasted with aspects of industrial applications from a constructive, but critical, viewpoint. Based on the status and trends within the field, future research is suggested with regard to both further development of the research area and industrial needs. By highlighting the industrial aspects, practitioners will hopefully see the benefit of using advanced decision support systems in complex situations related to combined inventory management and routing in their business. In addition, a classification and presentation of the research should help and motivate researchers to further focus on inventory management and routing challenges.

• Hoff, Arild; Andersson, Henrik; Christiansen, Marielle; Hasle, Geir & Løkketangen, Arne (2010). Industrial aspects and literature survey: Fleet composition and routing. Computers & Operations Research. ISSN 0305-0548. 37(12), p. 2041–2061. doi: 10.1016/j.cor.2010.03.015. Full text in Research Archive Show summary

  The purpose of this paper is to describe industrial aspects of combined fleet composition and routing in maritime and road-based transportation, and to present the current status of research in the form of a comprehensive literature review. First, presents a classification of problems, and then focuses on a basic definition of combined fleet composition and routing: the fleet size and mix vehicle routing problem. A basic mathematical formulation from the literature is presented. Further, the literature of extended and related problems is described and categorized. Surveys of application oriented research in road-based and maritime transportation conclude the review. Finally, we contrast the literature with aspects of industrial applications from a critical, but constructive stance. Major issues for future work are suggested.

• Hoff, Arild; Lium, Arnt-Gunnar; Løkketangen, Arne & Crainic, Teodor Gabriel (2010). A metaheuristic for stochastic service network design. Journal of Heuristics. ISSN 1381-1231. 16(5), p. 653–679. doi: 10.1007/s10732-009-9112-8. Full text in Research Archive Show summary

  This paper considers the time-dependent service network design problem with stochastic demand represented by scenarios. To our knowledge, this is the first attempt to address real life-size instances of this problem. The model integrates the balancing of empty vehicles, the cost of handling freight in intermediate terminals, the costs associated with moving freight using the selected services, and the penalty costs of not being able to deliver freight. A metaheuristic is presented and computational results are reported on a set of large new problem instances.

• Hoff, Arild; Gribkovskaia, Irina; Laporte, Gilbert & Løkketangen, Arne (2009). Lasso solution strategies for the vehicle routing problem with pickups and deliveries. European Journal of Operational Research. ISSN 0377-2217. 192(3), p. 755–766. doi: 10.1016/j.ejor.2007.10.021. Full text in Research Archive Show summary

  This paper considers the vehicle routing problem with pickups and deliveries (VRPPD) where the same customer may require both a delivery and a pickup. This is the case, for instance, of breweries that deliver beer or mineral water bottles to a set of customers and collect empty bottles from the same customers. It is possible to relax the customary practice of performing it pickup when delivering at it customer, and postpone the pickup until the vehicle has sufficient free capacity. In the case of breweries, these solutions will often consist of routes in which bottles are first delivered until the vehicle is partly unloaded, then both pickup and delivery are performed at the remaining customers, and finally empty bottles are picked Lip front the first visited customers. These customers are revisited in reverse order. thus giving rise to lasso shaped solutions. Another possibility is to relax the traditional problem even more and allow customers to be visited twice either in two different routes or at different times oil the same route, giving rise to it general solution. This article develops a tabu search algorithm capable of producing lasso solutions. A general solution can be reached by first duplicating each customer and generating a Hamiltonian solution oil the extended set of customers. Test results show that while general solutions outperform other solution shapes in term of cost. their computation cart be time consuming. The best lasso solution generated within it given time limit is generally better than the best general solution produced with the same computing effort. (c) 2007 Elsevier B.V. All rights reserved.

• Hoff, Arild & Løkketangen, Arne (2006). Creating lasso-solutions for the Traveling Salesman Problem with Pickup and Delivery by tabu search. Central European Journal of Operations Research. ISSN 1435-246X. 14(2), p. 125–140. doi: 10.1007/s10100-006-0164-7. Full text in Research Archive Show summary

  We consider the Traveling Salesman Problem with Pickup and Delivery (TSPPD) where the same costumers might require both deliveries of goods and pickup of other goods. All the goods should be transported from/to the same depot. A vehicle on a TSPPD-tour could often get some practical problems when arranging the load. Even if the vehicle has enough space for all the pickups, one has to consider that they are stored in a way that doesn't block the delivery for the next customer. In real life problems this occurs for instance for breweries when they deliver bottles of beer or mineral water and collects empty bottles from the same customers on the same tour. In these situations we could relax the constraints of only checking Hamiltonian tours, and also try solutions that can visit customers in a way giving rise to a 'lasso' model. A solution which first only delivers bottles until the vehicle is partly unloaded, then do both delivery and pickup at the remaining customers and at last picks up the empty bottles from the first visited customers, could in these situations be better than a pure Hamiltonian tour, at least in a practical setting. To find such solutions, we will use the metaheuristic Tabu Search on some well known TSPPD-problems, and compare them to other kinds of solutions on the same problems.

• Hoff, Arild & Løkketangen, Arne (1997). Finding prediction models by heuristic search. In Krogdahl, Stein (Eds.), Norsk informatikkonferanse '97. Tapir Akademisk Forlag. ISSN 9788251913614. p. 207–218. Full text in Research Archive
• Hoff, Arild; Løkketangen, Arne & Mittet, Ingvar (1996). Genetic algorithms for 0/1 multidimensional knapsack problems. In Aagesen, Finn Arve (Eds.), NIK '96 : Norsk informatikkonferanse : seksjon for IT og matematikk. Tapir Akademisk Forlag. ISSN 9788251913812. p. 291–301. Full text in Research Archive

View all works in NVA

• Hrydziushka, Darya; Hoff, Arild; Hvattum, Lars Magnus & Dominguez, Gregorio Tirado (2024). Evacuation model under conditions of uncertainty and damaged infrastructure. Full text in Research Archive
• Knudseth, Sunniva Haukvik; Hoff, Arild; Oppen, Johan & Hvattum, Lars Magnus (2023). Decision support for allocating farmed fish to customer orders using a bi-objective optimization model. Full text in Research Archive
• Hoff, Arild; Shaabani, Homayoun; Hvattum, Lars Magnus & Laporte, Gilbert (2023). A matheuristic for the multi-product maritime inventory routing problem. Full text in Research Archive
• Knudseth, Sunniva Haukvik; Molland, Even; Hoff, Arild; Hvattum, Lars Magnus & Oppen, Johan (2022). Decision Support for Allocating Farmed Fish to Customer Orders Using a Bi-objective Optimization Model. Full text in Research Archive
• Shaabani, Homayoun; Hoff, Arild; Hvattum, Lars Magnus & Laporte, Gilbert (2021). A matheuristic algorithm for maritime inventory routing problem. Full text in Research Archive
• Hoff, Arild; Hvattum, Lars Magnus & Danielsen, Ketil (2021). An application of the multi-depot heterogeneous fixed fleet open vehicle routing problem. Full text in Research Archive
• Saeed, Naima; Hoff, Arild & Larsen, Odd I (2019). The effect of the development of port’s inland hinterland transport technologies on the export of perishable products from South Africa. Full text in Research Archive Show summary

  This paper aims to analyze the impact of the development of a port’s inland hinterland transport technologies when exporting perishable products from the Republic of South Africa. The development of transport technologies is reflected in terms of a lower cost and higher frequency of inland transport. The Republic of South Africa has an extensive transport network. Its production centres are connected by road and rail to the leading trade ports. Despite a well-developed transport network, its traders face delays caused by domestic transportation. To investigate the interplay between export products, transport and market access for exporters, a linear programming model is presented in this paper. It is assumed that initially, two modes of transport are available for transportation of the export product from the farm to the "market." The two modes are trucks and railway, and analysis is extended by including intermodal transportation as a combination of railway and road. The model is solved with different numeric values for the parameters, to understand the roles of transport technologies, access improvements and the interplay between them.The results of the analysis show that the optimal strategy is to improve the rail infrastructure to offer more frequent rail services from the market to the port of Cape Town.

• Hoff, Arild; Peiro, Juanjo; Corberán, Ángel & Martí, Rafael (2019). Heuristics for the capacitated modular hub location problem. Full text in Research Archive
• Hoff, Arild; Berg, Brit Flemmen & Pasha, Urooj (2019). Collecting manures from local farms for a biogas plant in Norway. Full text in Research Archive
• Hoff, Arild; Martí, Rafael; Campos, Vicente & Peiró, Juanjo (2018). Heuristics for the Min-Max Arc Crossing Problem in Graphs. Full text in Research Archive
• Hoff, Arild; Martí, Rafael; Campos, Vicente & Peiró, Juanjo (2018). Heuristics for the Min-Max Arc Crossing Problem in Graphs. Full text in Research Archive
• Hoff, Arild; Peiró, Juanjo; Corberán, Ángel & Martí, Rafael (2018). Heuristics for the Capacitated Modular Hub Location Problem. Full text in Research Archive
• Hoff, Arild; Peiro, Juanjo; Corberán, Angel & Martí, Rafael (2016). Adaptive Memory Programming for the Capacitated Modular Hub Location Problem. Full text in Research Archive
• Pasha, Urooj; Hoff, Arild & Hvattum, Lars Magnus (2015). The Recurring Fleet Size and Mix Vehicle Routing Problem with Stochastic Demands. Full text in Research Archive
• Pasha, Urooj; Hoff, Arild & Hvattum, Lars Magnus (2014). The recurring fleet size and mix vehicle routing problem with stochastic demands. Full text in Research Archive
• Pasha, Urooj; Hoff, Arild & Løkketangen, Arne (2013). Milk collection in Western Norway using trucks and trailers. In Menou, Abdellah (Eds.), ISORAP 2013 International Symposium on Operational Research - Proceedings. The International Federation of Operational Research Societies (IFORS). ISSN 9789954322222. p. 343–350. Full text in Research Archive Show summary

  Collection and transportation of milk from farms to production factories is a crucial issue around the world. This problem can often be seen as a special case of the Truck and Trailer Vehicle Routing Problem (TTVRP) in which a trailer cannot be driven along with a truck to the farms and must be parked in the nearest available parking place while the truck visits farms and collects milk. Then, the truck returns to the parking place, transfers milk to the trailer and start a new sub route or continues the route with trailer. In this paper, we solve a real world planning and distribution problem for TINE SA which is the leading dairy company in Norway. A clustering technique followed by a heuristic based on tabu search is developed to solve this problem and computational results are reported.

• Pasha, Urooj; Hoff, Arild & Løkketangen, Arne (2013). The recurring fleet size and mix vehicle routing problem (R-FSMVRP). Full text in Research Archive
• Pasha, Urooj; Hoff, Arild & Løkketangen, Arne (2013). Milk collection in Western Norway using trucks and trailers. Full text in Research Archive
• Pasha, Urooj; Hoff, Arild & Løkketangen, Arne (2013). The Stochastic Repeated Fleet Size and Vehicle Routing Problem. Full text in Research Archive Show summary

  A new variant of the Fleet size and Mix Vehicle Routing Problem (FSMVRP) named as The Stochastic Repeated Fleet Size and Mix Vehicle Routing Problem (SR-FSMVRP) is introduced and defined in this paper. It is a non deterministic delivery problem. Different scenarios are generated with stochastic demand for a given set of customers. The objective is to find the solution with the lowest expected transportation cost for a given time period.

• Pasha, Urooj; Hoff, Arild & Løkketangen, Arne (2013). Milk collection in Western Norway using trucks and trailers. Full text in Research Archive
• Hoff, Arild; Pasha, Urooj & Løkketangen, Arne (2012). Milk collection in Western Norway using trucks and trailers. Full text in Research Archive Show summary

  Milk collection is a problem which is well known in rural areas all around the world. This talk considers a real world problem for a Norwegian dairy company collecting raw milk from farmers. Most farms are inaccessible for a large truck carrying a trailer. Thus the routes are organized as a main tour between larger parking spots where the trailer is left behind, and the truck drives subtours from this spots to visit the actual farms. The talk will present heuristics for constructing such tours and computational results comparing our result with the current plan of the company.

• Hoff, Arild (2012). Milk collection in Western Norway using trucks and trailers. Full text in Research Archive Show summary

  This paper considers a real world problem for a Norwegian dairy company collecting raw milk from farmers. The problem can be classified as a special type of the Truck and Trailer Routing Problem which is a variant of the traditional Vehicle Routing Problem. We will use the tabu search metaheuristic to construct the routes for the different strategies of milk collection.

• Hoff, Arild (2012). Milk Collection in Western Norway using Trucks and Trailers. Full text in Research Archive
• Hoff, Arild & Løkketangen, Arne (2011). Milk collection in Western Norway using trucks and trailers. Full text in Research Archive Show summary

  Milk collection is a problem which is well known in rural areas all around the world. This talk considers a real world problem for a Norwegian dairy company collecting raw milk from farmers. Most farms are inaccessible for a large truck carrying a trailer. Thus the routes are organized as a main tour between larger parking spots where the trailer is left behind, and the truck drives sub- tours from this spots to visit the actual farms. The talk will present heuristics for constructing such tours and computational results comparing our result with the current plan of the company.

• Løkketangen, Arne; Hoff, Arild & Pasha, Urooj (2010). New shrinking and expanding heuristics for the fleet size and mix vehicle routing problem. Full text in Research Archive
• Pasha, Urooj; Hoff, Arild & Løkketangen, Arne (2010). Switching vehicle strategyfor solving FSMVRP with tabu search. Full text in Research Archive
• Pasha, Urooj U.; Hoff, Arild & Løkketangen, Arne (2010). A shrinking and expanding heuristics for fleet size and mix vehicle routing problem. Full text in Research Archive
• Andersson, Henrik; Hoff, Arild; Christiansen, Marielle; Hasle, Geir & Løkketangen, Arne (2009). Inventory routing problems - Combined inventory management and routing. Full text in Research Archive Show summary

  In an inventory routing problem, inventory management is combined with a routing problem. It is an exciting problem within operations research since it offers both scientific challenges and is of great practical importance. This presentation will focus on these two aspects with a special emphasis on industrial applications. We will discuss different definitions of the problem and give a broad overview of the existing literature. The inventory routing problem is not one problem but rather a class of problems. Within this class, the differences are sometimes larger than the similarities, both regarding the assumptions made and the methodology used, and it is therefore of interest to classify the work that has been done and see what conclusions can be drawn from such a classification. Finally we will present some applications and discuss trends and future research.

• Hoff, Arild; Andersson, Henrik; Christiansen, Marielle; Hasle, Geir & Løkketangen, Arne (2009). Industrial fleet size and mix problems - a survey. Full text in Research Archive Show summary

  The purpose of this talk is to describe industrial aspects of combined fleet composition and routing in maritime and road-based transportation, and to present the current status of research in the form of a comprehensive literature review. With a backdrop of industrial aspects, a categorized survey of relevant literature since the first published papers in the 1950's is given. First, the literature review discusses some early seminal and application-oriented papers, presents a classification of problems, and then focuses on a basic definition of combined fleet composition and routing: the fleet size and mix vehicle routing problem. Different solution strategies are discussed and compared. Further, the literature of extended and related problems is described and categorized. Papers considering application oriented research in road-based and maritime transportation conclude the review. Finally, we contrast the literature with aspects of industrial applications from a critical, but constructive stance. Major issues for future work are suggested.

• Andersson, Henrik; Hoff, Arild; Christiansen, Marielle; Hasle, Geir & Løkketangen, Arne (2009). Industrial inventory routing problems. Full text in Research Archive Show summary

  In an inventory routing problem, inventory management is combined with a routing problem. It is an exciting problem within operations research since it offers both scientific challenges and is of great practical importance. This presentation will focus on these two aspects with a special emphasis on industrial applications. We will discuss different definitions of the problem and give a broad overview of the existing literature. The inventory routing problem is not one problem but rather a class of problems. Within this class, the differences are sometimes larger than the similarities, both regarding the assumptions made and the methodology used, and it is therefore of interest to classify the work that has been done and see what conclusions can be drawn from such a classification. Finally we will present some applications and discuss trends and future research.

• Hoff, Arild & Løkketangen, Arne (2009). Improving construction heuristics for inventory routing problems. Full text in Research Archive
• Løkketangen, Arne; Hoff, Arild; Lium, Arnt-Gunnar & Crainic, Teodor Gabriel (2008). A metaheuristic for stochastic service network design. Full text in Research Archive
• Hoff, Arild; Andersson, Henrik; Christiansen, Marielle; Hasle, Geir & Løkketangen, Arne (2008). Industrial aspects and literature survey : fleet composition and routing. Full text in Research Archive Show summary

  The purpose of this talk is to describe industrial aspects of combined fleet composition and routing in maritime and road-based transportation, and to present the current status of research in the form of a comprehensive literature review. With a backdrop of industrial aspects, a categorized survey of relevant literature since the first published papers in the 1950's is given. First, the literature review discusses some early seminal and application-oriented papers, presents a classification of problems, and then focuses on a basic definition of combined fleet composition and routing: the fleet size and mix vehicle routing problem. Three basic mathematical formulations from the literature are presented and compared. Further, the literature of extended and related problems is described and categorized. Surveys of application oriented research in road-based and maritime transportation conclude the review. Finally, we contrast the literature with aspects of industrial applications from a critical, but constructive stance. Major issues for future work are suggested.

• Hoff, Arild (2008). Heuristics for the LNG inventory routing problem. Full text in Research Archive Show summary

  The liquefied natural gas (LNG) inventory routing problem considered in this talk is the part of the supply chain between liquefaction of gas at loading terminals, shipping by LNG carriers and delivery at unloading terminals. Inventory limitations have to be obeyed. Purchase contracts with an upper and lower limit of delivery within an interval and origin-destination clauses are considered when planning routes. This talk will present the problem and suggest different heuristics for solving it.

• Løkketangen, Arne & Hoff, Arild (2007). Bedre planlegging av transport. 165(25.09.2007), p. 31–31. Full text in Research Archive
• Hoff, Arild; Andersson, Henrik; Christiansen, Marielle; Hasle, Geir & Løkketangen, Arne (2007). Industrial aspects and literature survey : fleet dimensioning and routing, Abstracts (url.). Nordic Section of Math Programming Society. p. 2–2. Full text in Research Archive Show summary

  The objective of this paper is to show the current status of research that combines fleet dimensioning and vehicle routing in maritime and road-based transportation. The paper shows an overview of the literature on this field since the first published papers in the 1950?s. The literature review includes some early papers regarding fleet sizing and focuses particularly on the Fleet Size and Mix Vehicle Routing Problem (FSMVRP) and some of its variants. Different mathematical models for the FSMVRP are presented and compared to each other. Several other related problems are presented, and research that treats the fleet dimensioning and routing issue in a strategic context are discussed in addition to real life problems on the same topic. We also point to similarities and differences between the two selected modi for transportation. The paper relates the literature with aspects of industrial applications with a critical, but constructive, look at the research conducted so far. Major issues for future work are suggested..

• Hoff, Arild & Løkketangen, Arne (2007). A tabu search approach for milk collection in Western Norway using trucks and trailers. Full text in Research Archive
• Andersson, Henrik; Christiansen, Marielle; Hasle, Geir; Hoff, Arild & Løkketangen, Arne (2007). Industrial Aspects and Literature Survey: Combined Inventory Management and Routing. Full text in Research Archive
• Løkketangen, Arne & Hoff, Arild (2006). Transportation of milk to dairies using trailers. Full text in Research Archive Show summary

  We address the problem of transportation of milk from farmers to dairies in rural Norway. Due to accessibility restrictions, the hangers are prohibited from entering the farms, and must be parked at designated spots. Milk is then collected by the main vehicle and then pumped to the trailer. We report from tests on real-world instances.

• Hoff, Arild; Løkketangen, Arne; Crainic, Teodor Gabriel & Lium, Arnt-Gunnar (2006). Stochastic service network design : solving large instances using metaheuristics. Full text in Research Archive
• Hoff, Arild; Laporte, Gilbert & Løkketangen, Arne (2005). Creating lasso-solutions for the pickup and delivery problem using tabu search. Full text in Research Archive
• Hoff, Arild; Løkketangen, Arne & Laporte, Gilbert (2005). Creating lasso-solutions for the pick-up and delivery problem using tabu search. Full text in Research Archive
• Hoff, Arild & Løkketangen, Arne (2004). Creating lasso-solutions for the TSPPD-problem by tabu-search. Full text in Research Archive Show summary

  We consider the Traveling Salesman Problem with Pickup and Delivery (TSPPD). We will use the metaheuristic Tabu Search to try to find good solutions to some well known TSPPD-problems. Instead of only checking Hamiltonian tours which visits every node exactly once, we will also try solutions that can visit nodes twice in a so called lasso-model. This will make a solution which only delivers to the first customers visited and then picks up the goods on the way back.

• Hoff, Arild & Løkketangen, Arne (1997). Finding prediction models by heuristic search. Full text in Research Archive
• Shaabani, Homayoun; Hvattum, Lars Magnus; Laporte, Gilbert & Hoff, Arild (2023). Stability metrics for a maritime inventory routing problem under sailing time uncertainty. Høgskolen i Molde - Vitenskapelig høgskole i logistikk. ISSN 9788279623427. Full text in Research Archive
• Hoff, Arild; Lium, Arnt-Gunnar; Løkketangen, Arne & Crainic, Teodor Gabriel (2009). A metaheuristic for stochastic service network design. University Research Centre on Enterprise Networks, Logistics and Transportation. Full text in Research Archive Show summary

  This paper considers the time-dependent service network design problem with stochastic demand represented by scenarios. To our knowledge, this is the first attempt to address real life-size instances of this problem. The model integrates the balancing of empty vehicles, the cost of handling freight in intermediate terminals, the costs associated with moving freight using the selected services, and the penalty costs of not being able to deliver freight. A metaheuristic method is presented and computational results are reported on a set of large new problem instances

• Hoff, Arild & Løkketangen, Arne (2008). A tabu search approach for milk collection in Western Norway using trucks and trailers. Høgskolen i Molde - Vitenskapelig høgskole i logistikk. ISSN 9788279620952. Full text in Research Archive Show summary

  This paper considers a real world problem for a Norwegian dairy company collecting raw milk from farmers. The problem can be classified as a special type of the Truck and Trailer Routing Problem which is a variant of the traditional Vehicle Routing Problem. The company uses a fleet of heterogeneous trucks with tanks for the milk, and a truck can either drive the route by itself or carry a trailer with an additional tank. Most Norwegian farms are small and inaccessible for vehicles with trailers, so the routes that are served with a trailer have to be constructed so that the vehicles carry the trailer to a parking place and leave it there. The truck will then drive a subtour to the farmers and collect milk before it returns to the parked trailer. It can then fill the milk over from the truck tank to the trailer tank and start on a new subtour from the same spot, or it can drive the trailer to a new parking place, fill the milk over and start a subtour from there. The milk can be stored up to three days at the farms, and in this paper we will compare different frequencies of collection, different sizes of the vehicles and the benefit of using trailers compared to driving with single trucks. We will use the tabu search metaheuristic to construct the routes for the different strategies of milk collection.

• Hoff, Arild; Andersson, Henrik; Christiansen, Marielle; Hasle, Geir & Løkketangen, Arne (2008). Industrial Aspects and Literature Survey: Fleet Composition and Routing. SINTEF Digital. ISSN 9788214043976. Full text in Research Archive Show summary

  The purpose of this paper is to describe industrial aspects of combined fleet composition and routing in maritime and road-based transportation, and to present the current status of research in the form of a comprehensive literature review. With a backdrop of industrial aspects, a categorized survey of relevant literature since the first published papers in the 1950’s is given. First, the literature review discusses some early seminal and application-oriented papers, presents a classification of problems, and then focuses on a basic definition of combined fleet composition and routing: the fleet size and mix vehicle routing problem. Three basic mathematical formulations from the literature are presented and compared. Further, the literature of extended and related problems is described and categorized. Surveys of application oriented research in road-based and maritime transportation conclude the review. Finally, we contrast the literature with aspects of industrial applications from a critical, but constructive stance. Major issues for future work are suggested. Oppdragsgiver: Research Council of Norway

• Andersson, Henrik; Hoff, Arild; Christiansen, Marielle; Hasle, Geir & Løkketangen, Arne (2008). Industrial Aspects and Literature Survey: Combined Inventory Management and Routing. SINTEF Digital. ISSN 9788214043990. Full text in Research Archive Show summary

  This paper describes industrial aspects of combined inventory management and routing, and gives a comprehensive literature review of the current state of the research. First there is a classification of types of supply chains, followed by conditions for when inventory management and routing can be combined, and the current industrial practice. The literature related to the basic problem, as well as extended and related problems is described and classified. The literature is finally contrasted with aspects of industrial applications from a constructive, but critical, viewpoint. Suggestions for where the research in this area should go, is also suggested. Oppdragsgiver: Research Council of Norway

• Hoff, Arild; Lium, Arnt-Gunnar; Løkketangen, Arne & Crainic, Teodor Gabriel (2007). A metaheuristic for stochastic service network design. University Research Centre on Enterprise Networks, Logistics and Transportation. Full text in Research Archive Show summary

  This paper considers the time-dependent service network design problem with stochastic demand represented by scenarios. To our knowledge, this is the first attempt to address real life-size instances of this problem. The model integrates the balancing of empty vehicles, the cost of handling freight in intermediate terminals, the costs associated with moving freight using the selected services, and the penalty costs of not being able to deliver freight. A metaheuristic method is presented and computational results are reported on a set of large new problem instances

• Hoff, Arild (2006). Heuristics for rich vehicle routing problems. Høgskolen i Molde - Vitenskapelig høgskole i logistikk. ISSN 9788279620730. Full text in Research Archive

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