Mustafa S. Canbolat

A web-based decision support system for multi-criteria inventory classification using fuzzy AHP methodology

We propose an inventory classification system based on the fuzzy analytic hierarchy process (AHP), a commonly used tool for multi-criteria decision making problems. We integrate fuzzy concepts with real inventory data and design a decision support system assisting a sensible multi-criteria inventory classification. We report on a study conducted in a small electrical appliances company and validate the design of the proposed multi-criteria inventory classification system and its underlying fuzzy AHP model.

The rectilinear distance Weber problem in the presence of a probabilistic line barrier

This paper considers the problem of locating a single facility in the presence of a line barrier that occurs randomly on a given horizontal route on the plane. The objective is to locate this new facility such that the sum of the expected rectilinear distances from the facility to the demand points in the presence of the probabilistic barrier is minimized. Some properties of the problem are reported, a solution algorithm is provided with an example problem, and some future extensions to the problem are discussed.

A strategic decision framework for a value added supply chain

Supply chains are becoming increasingly complex. The structure of the supply chain and the suppliers who participate in it are critical decisions for managers. The supply chain is no longer simply a source of inputs or services but an integral source of value added. It is clear that in some cases strategic supply chain objectives may require trade-offs, for example, between cost and innovation capability or between managing risk and maximising flexibility. These decisions balancing trade-offs between desirable partner characteristics are critical and can make a significant contribution to business performance. A framework is outlined, based on the foundation of extant literature, within which firms can make strategic decisions on supply chain structure by categorising the characteristics they prioritise in their supply chain strategy. There is also a strong foundation in the literature on developing mathematical models that provide insight into the decision-making process. A mixed integer programming model is specified that incorporates the opportunity for diversification and provides a demand allocation decision. The model is robust enough to allow for single or diversified supplier strategies based not only on capacity constraints but also on risk pooling and minimum performance requirements for key characteristics that form the basis of the strategy. A Lagrangian relaxation is proposed and satisfactory performance results are provided.

Locating emergency facilities with random demand for risk minimization

Locating emergency service facilities is a challenging problem. Planners do not know specifically where emergencies will occur and, therefore, struggle to find a location that effectively ensures that the risk of poor service to any specific emergency is minimized. In this paper, we study the problem where locations of each demand point (emergency occurence) are random. Our objective is to minimize the expected maximum rectilinear distance from the facility to the demand points. This problem has practical importance in public sector as it aims to minimize the expected maximum risk when locating an emergency response facility. We start with a one dimensional problem and extend the results to the more complex two dimensional case. We present some properties of the problem along with examples for special cases. We propose a simulation approach to solving complex two dimensional cases and present simulation results for general cases to illustrate the problem and provide insight into solutions. We show that the simulation approach provides solutions very close to optimal for the linear case and suggest that it may provide valuable insight into the location selection system.

On the use of the Varignon frame for single facility Weber problems in the presence of convex barriers

This paper presents a new experimental approach to the Weber problem in the presence of convex barriers by using the Varignon frame. The Varignon frame is a mechanical system of strings, weights and a board with holes that has been used to identify an optimal location for the classical Weber problem. We show through analytical results that the same analog can also be used for some of the Weber problems in the presence of barriers. Some examples from the literature are revisited through experiments. Findings are compared to those found in the literature. Practical use of the analog is discussed as it provides rapid solutions, allows for flexibility, and enables one to visualize the problem.

A planar single facility location and border crossing problem

In this study, we tackle the problem of locating a facility in a region where a fixed line barrier divides the region into two. The resulting subregions communicate with each other through a number of passage points located on the line barrier. Our contribution is threefold. First, we formulate the problem as a Mixed Integer Nonlinear Programming (MINLP) model and provide an optimal solution methodology based on an Outer Approximation (OA) algorithm. Second, we discuss the minimax version of this problem for locating an emergency facility and use the OA algorithm to solve the problem. We then provide simple example problems and extensive computational results for both problems. Finally, we propose a one-infinity approximation approach for the latter problem which yields a linear model. Practical uses of the models have been discussed in the border crossing context.

Optimal Allocation of LDOs and Decoupling Capacitors within a Distributed On-Chip Power Grid

Parallel on-chip voltage regulation, where multiple regulators are connected to the same power grid, has recently attracted significant attention with the proliferation of small on-chip voltage regulators. In this article, the number, size, and location of parallel low-dropout (LDO) regulators and intentional decoupling capacitors are optimized using mixed integer non-linear programming formulation. The proposed optimization function concurrently considers multiple objectives such as area, power noise, and overall power consumption. Certain objectives are optimized by putting constraints on the other objectives with the proposed technique. Additional constraints have been added to avoid the overlap of LDOs and decoupling capacitors in the optimization process. The results of an optimized LDO allocation in the POWER8 chip is compared with the recent LDO allocation in the same IBM chip in a case study where a 20% reduction in the noise is achieved. The results of the proposed multi-criteria objective function under a different area, power, and noise constraints are also evaluated with a sample ISPD’11 benchmark circuits in another case study.

How should marketers deal with growth pattern changes in viral marketing campaigns

The impact of environmental shifts to growth trajectory of viral marketing is critical. Advertisers should recognise the growth pattern changes, termed regime change, in order to efficiently and effectively execute viral marketing campaigns. A surprising variety of growth patterns are evident. There are multiple models of viral growth and all of them assume a single growth model with changes in parameters. A better approach that supports decision making should allow for the incorporation of sequential functional forms. The model presented incorporates regime change and therefore allows for multiple functional forms. There are multiple competing approaches to identifying change points, a line of separation between functional forms. The paper focuses on regime change and change point analysis in the viral marketing context. A simple two-form model is proposed as a starting point to capture many likely viral growth situations. A five step process is presented to facilitate this model.