A heuristic method to schedule training programs for Small and Medium Enterprises

in European Journal of Operational Research (2012), 217

During the life period of Small and Medium Enterprises (SMEs) in incubators they need some training programs to acquire the required knowledge in order to survive and succeed in the business environment ... [more ▼]

During the life period of Small and Medium Enterprises (SMEs) in incubators they need some training programs to acquire the required knowledge in order to survive and succeed in the business environment. This paper presents a heuristic method based on an optimization model to schedule these programs at the most suitable times. Based on the proposed heuristic, each training program is implemented in a suitable time by considering the SMEs’ requirements and some other logical constraints. The proposed heuristic is described in detail, and its implementation is demonstrated via a real-life numerical example. The numerical results of the heuristic are compared with other methods. [less ▲]

Competitive facility location problem with attractiveness adjustment of the follower: A bilevel programming model and its solution

in European Journal of Operational Research (2011), 208(3), 206-220

We are concerned with a problem in which a firm or franchise enters a market by locating new facilities where there are existing facilities belonging to a competitor. The firm aims at finding the location ... [more ▼]

We are concerned with a problem in which a firm or franchise enters a market by locating new facilities where there are existing facilities belonging to a competitor. The firm aims at finding the location and attractiveness of each facility to be opened so as to maximize its profit. The competitor, on the other hand, can react by adjusting the attractiveness of its existing facilities with the objective of maximizing its own profit. The demand is assumed to be aggregated at certain points in the plane and the facilities of the firm can be located at predetermined candidate sites. We employ Huff's gravity-based rule in modeling the behavior of the customers where the fraction of customers at a demand point that visit a certain facility is proportional to the facility attractiveness and inversely proportional to the distance between the facility site and demand point. We formulate a bilevel mixed-integer nonlinear programming model where the firm entering the market is the leader and the competitor is the follower. In order to find the optimal solution of this model, we convert it into an equivalent one-level mixed-integer nonlinear program so that it can be solved by global optimization methods. Apart from reporting computational results obtained on a set of randomly generated instances, we also compute the benefit the leader firm derives from anticipating the competitor's reaction of adjusting the attractiveness levels of its facilities. The results on the test instances indicate that the benefit is 58.33% on the average. [less ▲]

The tool switching problem revisited

in European Journal of Operational Research (2007), 182(2), 952-957

In this note we study the tool switching problem with non-uniform tool sizes. More specifically, we consider the problem where the job sequence is given as part of the input. We show that the resulting ... [more ▼]

In this note we study the tool switching problem with non-uniform tool sizes. More specifically, we consider the problem where the job sequence is given as part of the input. We show that the resulting tooling problem is strongly N P-complete, even in case of unit loading and unloading costs. On the other hand, if the capacity of the tool magazine is also given as part of the input, we show that the problem is solvable in polynomial time. These results settle the complexity of a relevant variant of the tool switching problem. (C) 2006 Elsevier B.V. All rights reserved. [less ▲]

Optimal procurement decisions in the presence of total quantity discounts and alternative product recipes

in European Journal of Operational Research (2004), 159(2), 364-378

We describe the purchasing decisions faced by a multi-plant company. The suppliers of this company offer complex discount schedules based on the total quantity (rather than cost) of ingredients purchased ... [more ▼]

We describe the purchasing decisions faced by a multi-plant company. The suppliers of this company offer complex discount schedules based on the total quantity (rather than cost) of ingredients purchased. The schedules simultaneously account both for corporate purchases and for purchases at the individual plant level. The complexity of the purchasing decisions is further increased due to the existence of alternative production recipes for each final product. We formulate the corresponding cost-minimization problem as a nonlinear mixed 0-1 programming problem. We propose various ways to linearize this formulation, and we evaluate the quality of the resulting models on real-world data. (C) 2003 Elsevier B.V. All rights reserved. [less ▲]

A comparison of parametric and non-parametric distance functions: with application to European Railways

in European Journal of Operational Research (1999), (117), 326-339

In this paper we use multi-output distance functions to investigate technical inefficiency in European railways. The principle aim of the paper is to compare the results obtained from the three ... [more ▼]

In this paper we use multi-output distance functions to investigate technical inefficiency in European railways. The principle aim of the paper is to compare the results obtained from the three alternative methods of estimating multioutput distance functions. Namely, the construction of a parametric frontier using linear programming; data envelopment analysis (DEA) and corrected ordinary least squares (COLS). Input-orientated, output-orientated and constant returns to scale (CRS) distance functions are estimated and compared. The results indicate a strong degree of correlation between the input- and output-orientated results for each of the three methods. There are also significant correlations observed between the results obtained using the alternative estimation methods. The strongest correlations being between the parametric linear programming and the COLS methods. Finally, the paper concludes with the suggestion that a combination of the technical efficiency scores, obtained from the three different methods, be used as the preferred set of scores. This idea is borrowed from the time-series forecasting literature. [less ▲]