Evolutionary multiobjective optimization of the multi-location transshipment problem

We consider a multi-location inventory system where inventory choices at each location are centrally coordinated. Lateral transshipments are allowed as recourse actions within the same echelon in the inventory system to reduce costs and improve service level. However, this transshipment process usually causes undesirable lead times. In this paper, we propose a multiobjective model of the multi-location transshipment problem which addresses optimizing three conflicting objectives: (1) minimizing the aggregate expected cost, (2) maximizing the expected fill rate, and (3) minimizing the expected transshipment lead times. We apply an evolutionary multiobjective optimization approach using the strength Pareto evolutionary algorithm (SPEA2), to approximate the optimal Pareto front. Simulation with a wide choice of model parameters shows the different trades-off between the conflicting objectives

"Choice of Air Cargo Transshipment Airport: An Application to Air Cargo Traffic to/from Northeast Asia"

Based on a unique data set of 760 air cargo transshipment routings to/from the Northeast Asian region in 2000, this paper applies an aggregate form of multinomial logit model to identify the critical factors influencing air cargo transshipment route choice decisions. The analysis focuses on the trade-off between monetary cost and time cost while considering other variables relevant for choice of transshipment airport. The estimation method considers the presence of unobserved attributes, and corrects for resulting endogeneity via a two-stage least squares estimation using instrumental variables. Our empirical results show that choice of air cargo transshipment hub is more sensitive to time cost than the monetary costs such as landing fees and line-haul price. For example, our simulation results suggest that a one-hour reduction in total transport and processing time for a particular O-D air cargo traffic would be more effective than a US$1,000 reduction in airport charges. This suggests that it is important to reduce air cargo connecting time at an airport via adequate investment in capacity and automation even by increasing landing and other airport charges.

Near-Optimal Approximate Shortest Paths and Transshipment in Distributed and Streaming Models

We present a method for solving the transshipment problem - also known as uncapacitated minimum cost flow - up to a multiplicative error of $1 + \varepsilon$ in undirected graphs with non-negative edge weights using a tailored gradient descent algorithm. Using $\tilde{O}(\cdot)$ to hide polylogarithmic factors in $n$ (the number of nodes in the graph), our gradient descent algorithm takes $\tilde O(\varepsilon^{-2})$ iterations, and in each iteration it solves an instance of the transshipment problem up to a multiplicative error of $\operatorname{polylog} n$. In particular, this allows us to perform a single iteration by computing a solution on a sparse spanner of logarithmic stretch. Using a randomized rounding scheme, we can further extend the method to finding approximate solutions for the single-source shortest paths (SSSP) problem. As a consequence, we improve upon prior work by obtaining the following results: (1) Broadcast CONGEST model: $(1 + \varepsilon)$-approximate SSSP using $\tilde{O}((\sqrt{n} + D)\varepsilon^{-3})$ rounds, where $D$ is the (hop) diameter of the network. (2) Broadcast congested clique model: $(1 + \varepsilon)$-approximate transshipment and SSSP using $\tilde{O}(\varepsilon^{-2})$ rounds. (3) Multipass streaming model: $(1 + \varepsilon)$-approximate transshipment and SSSP using $\tilde{O}(n)$ space and $\tilde{O}(\varepsilon^{-2})$ passes. The previously fastest SSSP algorithms for these models leverage sparse hop sets. We bypass the hop set construction; computing a spanner is sufficient with our method. The above bounds assume non-negative edge weights that are polynomially bounded in $n$; for general non-negative weights, running times scale with the logarithm of the maximum ratio between non-zero weights.Comment: Accepted to SIAM Journal on Computing. Preliminary version in DISC 2017. Abstract shortened to fit arXiv's limitation to 1920 character

Inventory control policy of preventive lateral transshipment between retailers in multi periods

Purpose: Preventivelateral transshipment can respond to customers who will choose a substitute or to give up when the product is out of stock. Motivatedby the common practice, adecision-making model of preventive lateral transshipment with multi sellingperiods is developed. The purpose of the paper is to explore the optimal preventive lateral transshipment policy with multi selling periods. Design/methodology/approach: With adiscrete-time dynamic programming model, we take a dynamic programming approach and adopt backward induction to analyze two retailers’ preventive lateral transshipment policy. Findings: The optimal preventivelateral transshipment policy is a threshold policy which depends on both theremaining selling periods and inventory level. The above properties ensure thattwo retailers can control inventory with preventive lateral transshipment. Practical implications: The retailer can adjust inventory via the thresholdtype policy. The simple decisionrule which compares on-hand inventory level with the critical inventory level can be used to control inventory by preventive lateral transshipment. Originality/value: A discrete-timedecision-making model of preventive lateral transshipment policy isformulated. This model takes consideration of multi selling periods, whichis different from most existing researches on preventive lateraltransshipment.Peer Reviewe

Service Parts Inventory Control with Lateral Transshipment that Takes Time

In equipment-intensive industries such as truck manufacturing, electronics manufacturing, photo copiers, and airliners, service parts are often slow moving items for which, in some cases, the transshipment time is not negligible. However, this aspect is hardly considered in the existing spare parts literature. We assess the effect of non-negligible lateral transshipment time on various aspects of spare parts inventory control. Furthermore, we introduce customer-oriented service levels by taking the uncommitted pipeline stocks into account. A case study in the dredging industry shows that lateral transshipment may lead to lower system performance, which supports the results from some recent studies. Furthermore, we find that considerable savings can be obtained when we include the uncommitted pipeline stocks in both base stock allocation and lateral transshipment decisions.inventory control;METRIC;customer-oriented service level;lateral transshipment

Closing the Gap: Comparing Tuna Rfmo Port State Measures with the Fao Agreement on Port State Measures

The Pew Environment Group has conducted a gap analysis comparing the port State measures (PSMs) established by 10 Regional Fisheries Management Organisations (RFMOs) with those established by the United Nations Food and Agriculture Organization (FAO) Agreement on Port State Measures to Prevent, Deter and Eliminate Illegal, Unreported and Unregulated Fishing (PSMA, or Agreement). The research assessed the extent to which measures adopted by these RFMOs meet the PSMA standards, and identified those aspects that need to be further developed by each RFMO in order for its measures to become aligned with the Agreement's. The newly adopted PSMA sets an international minimum standard on PSMs and provides a unique opportunity to harmonise and strengthen port State controls globally. RFMOs have a special role to play in this process, specifically in helping to combat illegal, unreported and unregulated (IUU) fishing on the high seas. This report presents the final results of the gap analysis research conducted for the five tuna RFMOs based on information that was publicly available up to 30 April 2011. As part of our methodology, we shared the preliminary results of each RFMO gap analysis with the Secretariats of all 10 RFMOs and, through them, also with their Contracting Parties (CPs). We would like to thank those RFMO Secretariats and CPs that provided us with comments, many of which were extensive. We have taken all the comments received into consideration and revised our preliminary analyses where necessary. The analysis focused on a single set of tools available to combat IUU fishing, namely PSMs adopted by RFMOs, and did not examine other measures adopted by governments or any of the reviewed RFMOs, such as flag State controls or market measures not taken at port. Our assessment of the degree of conformity between each RFMO's PSMs and the PSMA does not reflect the overall performance of that RFMO in its efforts to combat IUU fishing. The aim of this exercise was to identify specific gaps in PSMs adopted by these RFMOs as they compare to the PSMA, and to make clear recommendations on how they could be strengthened. The goal of this research is to offer information that RFMOs could use to strengthen their own port State control systems and, as a result, contribute to enhanced harmonisation of PSMs across tuna fisheries around the world, with the aim of helping to further combat IUU fishing. With the exception of the Indian Ocean Tuna Commission (IOTC), which has adopted a resolution that includes most of the substantive duties of the PSMA, overall the tuna RFMOs do not meet the new international minimum standard set by the PSMA. In particular, they do not have strong PSMs in place and the PSMs that they have adopted are quite fragmented. Our analysis shows the following gaps: ? few requirements to share information between States and RFMOs; ? inadequate designation of ports for entry of foreign vessels; ? poor prior-to-entry information requirements for vessels approaching ports; ? insufficient restrictive measures for IUU fishing vessels, e.g. denial of port services, landing or transshiping; ? generally weak inspection systems; ? limited duties for flag States to cooperate with port State actions. We recognise that IUU fishing on the high seas is a common challenge for all RFMOs and that IUU fishing vessels are not limited to one ocean or RFMO Convention Area. Thus, the more that RFMOs apply a common standard on PSMs, the better able they will be to address this challenge. The comparative analyses undertaken here point to clear steps that RFMOs can take if they want to reach the new international standard provided by the PSMA, and thus make significant progress in combating IUU fishing

Network problems & algorythms

Special structure linear programming problems have received considerable attention during the last two decades and among them network problems are of particular importance and have found numerous applications in manage- ment science and technology. The mathematical models of the shortest route, maximal flow, and pure minimum cost flow problems are presented and various interrelationships among them are investigated. Finally three algorithms due to Dijkstra and Ford and Fulkerson which deal with the solution of the above three network problems are discussed