Modeling Freight Markets for Coal

In this paper we study bulk shipping of coal between the central regions in the world. We compare the performance of cost-minimizing models with a gravity model approach. The main finding in the paper is that cost minimizing models provide relative poor fits to data. A simple one parameter gravity model, however, provides very satisfactory fits to observed behaviour.Bulk freight; cost efficiency; gravity modeling

Searching for optimal integer solutions to set partitioning problems using column generation

We describe a new approach to produce integer feasible columns to a set partitioning problem directly in solving the linear programming (LP) relaxation using column generation. Traditionally, column generation is aimed to solve the LP relaxation as quick as possible without any concern of the integer properties of the columns formed. In our approach we aim to generate the columns forming the optimal integer solution while simultaneously solving the LP relaxation. By this we can remove column generation in the branch and bound search. The basis is a subgradient technique applied to a Lagrangian dual formulation of the set partitioning problem extended with an additional surrogate constraint. This extra constraint is not relaxed and is used to better control the subgradient evaluations. The column generation is then directed, via the multipliers, to construct columns that form feasible integer solutions. Computational experiments show that we can generate the optimal integer columns in a large set of well known test problems as compared to both standard and stabilized column generation and simultaneously keep the number of columns smaller than standard column generation

Mixed contracts for the newsvendor problem with real options

In this paper we consider the newsvendor model with real options. We consider a mixed contract where the retailer can order a combination of q units subject to the conditions in a classical newsvendor contract and Q real options on the same items. We provide a closed form solution to this mixed contract when the demand is discrete and study some of its properties. We also offer an explicit solution for the continuous case. In particular we demonstrate that a mixed contract may be superior to a real option contract when a manufacturer has a bound on how much variance she is willing to accept.Newsvendor model; real options; discrete demand; mixed contract

A maximum entropy approach to the newsvendor problem with partial information

In this paper, we consider the newsvendor model under partial information, i.e., where the demand distribution D is partly unknown. We focus on the classical case where the retailer only knows the expectation and variance of D. The standard approach is then to determine the order quantity using conservative rules such as minimax regret or Scarf's rule. We compute instead the most likely demand distribution in the sense of maximum entropy. We then compare the performance of the maximum entropy approach with minimax regret and Scarf's rule on large samples of randomly drawn demand distributions. We show that the average performance of the maximum entropy approach is considerably better than either alternative, and more surprisingly, that it is in most cases a better hedge against bad results.Newsvendor model; entropy; partial information

Some new bounds for the travelling salesman problem

The Clarke and Wright heuristic for the travelling salesman problem (TSP) has been used for several decades as a tool for finding good solutions for TSP and other vehicle routing problems (VRP). In this paper we offer a simple, but fundamental relationship between the cost of a Hamiltonian cycle measured in the original cost matrix and the cost of the same cycle measured in a saving matrix. This relationship leads to a new and simple lower bound for TSP that some times is better than more traditional bounds based on so-called 1-trees. We also offer some upper bounds for the optimal solution of TSP. Some examples are given in order to illustrate the new bounds and compare these with the classical ones

The comparative analysis of the NHH and BI networks

Based on the co-authorship networks of the Norwegian School of Economics (NHH) and the BI Norwegian Business School we present a comparative analysis in terms of structures, collaborations and publications. The networks’ structures are based on the NHH and the BI faculties’ publications recognized by the ISI Web of Science for the period 1950 – Spring, 2014. The analysed networks cover the publication activities of the NHH and the BI faculty members based on the data retrieved from ISI Web of Science in Spring, 2014

Shapley-Based Stackelberg Leadership Formation in Networks

In the given research we study a leadership formation of the most influential nodes in networks. Specifically, we analyze the competition between a leader and a follower based on the Stackelberg leadership model. Applying the concept of Shapley value to measure node’s importance, we represent the mechanism of Shapley-based Stackelberg leadership formation in networks. The approach is tested and represented in tabular and graphical formats

Internal pricing in supply chains

A supply chain is two or more parties linked by a flow of goods, information and funds. Since this means that supply chain management concerns environments in which there are multiple decision makers, which may be different firms or different divisions within a single firm, attention has to be focused on methods or mechanisms that improve system efficiencies. The reason for this is that in a supply chain setting, behavior that is locally rational can be inefficient from a global perspective. In this paper we will focus on the use of a negotiated two-part tariff for internal pricing as a means to achieve "channel co-ordination". The two-part internal pricing scheme can be thought of both as a means of handling risk sharing within a supply chain and to avoid the problem of double marginalization

A New Semi-Lagrangean Relaxation for the K-Cardinality Assignment Problem

Recently Beltrán-Royo, Vial & Alonso-Ayuso (2012) presented a semi-Lagrangean relaxation for the classical p-median location problem and for the incapacitated facility location problem. The results, obtained using the semi-Lagrangean relaxation approach, were quite impressive. In this paper we use a semi-Lagrangean relaxation to obtain an efficient solution method for the kcardinality assignment problem. The method has only one semi-Lagrangean multiplier that can only take on a limited number of values, making the search for the optimal multiplier easy. Since the semi-Lagrangean relaxation closes the duality gap, this leads to an extremely reliable and easily implementable method for finding k-cardinality assignments in large-scale cases. The method is computationally tested on the examples commonly used in the literature

The coauthorship network analysis of the Norwegian school of economics

We construct the coauthorship network based on the scientific collaboration between the faculty members at the Norwegian School of Economics (NHH) and based on their international academic publication experience. The network structure is based on the NHH faculties’ publications recognized by the ISI Web of Science for the period 1950 – Spring, 2014. The given network covers the publication activities of the NHH faculty members (over six departments) based on the information retrieved from the ISI Web of Science in Spring, 2014. In this paper we analyse the constructed coauthorship network in different aspects of the theory of social networks analysis