Kemal Altinkemer

Parallel Savings Based Heuristics for the Delivery Problem

The delivery problem consists of finding a set of routes for a fleet of capacitated vehicles to satisfy the cargo delivery requirements of customers. The vehicles are located in a central depot, and have to fulfill the delivery requirements in a sequence that minimizes total delivery costs. Each vehicle tour starts and terminates at the central depot, and each node is supplied by exactly one vehicle. All vehicles have the same cargo carrying capacity. The paper presents parallel savings algorithms PSAs for generating feasible solutions to this problem. The new algorithms combine the savings approach, with matching based procedures. In computational tests the heuristic produces better solutions than the best known solutions for six problems out of a standard set of 14 difficult test problems. Augmented Lagrangian based lower bounding procedures are developed, and used to evaluate the quality of the solutions generated by PSAs. The lower bounds generated by the augmented Lagrangian are the tightest bounds known for delivery problems. The performance of the PSAs is also compared to tour partitioning based heuristics which have better worst case error bounds. The average quality of solutions generated by PSAs is shown to be significantly superior on large sets of test problems.

Backbone Network Design Tools with Economic Tradeoffs

This paper studies the problem of assigning capacities to the links in a backbone network and determining the primary routes used by messages for each origin-destination communicating pair in the network. The topology of the backbone network is assumed to be known and the end to end traffic requirements are given. The problem is to find the least cost design where the system costs are composed of connection costs which depend on link capacities and queueing costs which are incurred by users due to the limited capacities of links. The goal is to determine the routing and link capacities simultaneously. The problem is formulated and lower bounds are obtained by Lagrangean relaxation embedded in a subgradient optimization procedure. Cut constraints which are redundant in the original formulation are introduced, they improve the lower bounds. A heuristic method based on the Lagrangean solution is described. Extensive computational results are reported. INFORMS Journal on Computing, ISSN 1091-9856, was publish...

The single-item lot-sizing problem with immediate lost sales

Abstract We introduce a profit maximization version of the well-known Wagner–Whitin model for the deterministic uncapacitated single-item lot-sizing problem with lost sales. Demand cannot be backlogged, but it does not have to be satisfied, either. Costs and selling prices are assumed to be time-variant, differentiating our model from previous models with lost sales. Production quantities and levels of lost sales in different periods represent a twofold decision problem. We first transform the total profit function into a special total cost function. We then prove several properties of an optimal solution. A forward recursive dynamic programming algorithm is developed to solve the problem optimally in O( T 2 ) time, where T denotes the number of periods in the problem horizon. The proposed algorithm can solve problems of sizes up to 400 periods in less than a second on a 500 MHz Pentium ® III processor.

Optimization of printed circuit board manufacturing: Integrated modeling and algorithms

This paper focuses on an integrated optimization problem that is designed to improve productivity in printed circuit board (PCB) manufacturing. We examine the problems of allocating the components to feeders and sequencing the placement of these components on the PCBs, populated by a rotary head machine with surface mount technology. While previous research focuses on sequencing the placement and only considers this subproblem as part of an interrelated set of problems, we provide an integrated approach which tackles all subproblems simultaneously as a single problem. Given an e-approximation algorithm for the vehicle routing problem we present a solution with an e-error gap for the PCB problem. ” 2000 Elsevier Science B.V. All rights reserved.

Technical Note—Heuristics for Delivery Problems with Constant Error Guarantees

In this paper Q Iterated Optimal Tour Partitioning, and Best Optimal Tour Partitioning algorithms are studied and analyzed for their worst case error. Both algorithms are based on partitioning an optimal traveling salesman tour in order to generate a feasible solution to the unit weight delivery problem. They have a worst case error bound of 2 − 1/ Q where Q is the maximal number of customers a vehicle could visit and N is the total number of customers. Similar worst case error bounds are shown when the algorithms are applied to an α-optimal traveling salesman tour.

A location-routing problem for the conversion to the "click-and-mortar" retailing: The static case

The static conversion from brick-and-mortar retailing to the hybrid click-and-mortar business model is studied from the perspective of distribution logistics. Retailers run warehouses and brick-and-mortar stores to meet the demand of their walk-in customers. When they decide to operate on the Web as an e-tailer, also click-and-mortar stores are needed which can serve both walk-in and online customers. While the distance between home and the nearest open store is used as a proxy measure for walk-in customers, a quality of service (QoS) guarantee for online customers is timely delivery of their orders. We describe and solve a static location-routing based problem for companies that embrace the clicks-and-bricks strategy in their retail operations. An augmented Lagrangian relaxation method embedded in a subgradient optimization procedure generates lower bounds, whereas a heuristic method finds feasible solutions. The performance of the Lagrangian-based solution method is tested on a number of randomly generated test problems.

Productivity and Performance Effects of Business Process Reengineering: A Firm-Level Analysis

We empirically investigate whether business process reengineering (BPR), which requires substantial investment in information technology to integrate separate tasks into complete cross-functional processes, is associated with enhanced firm productivity and performance. We analyze firm-level panel data covering the period 1987-2008 using fixed effects and first differencing, standard methods that account for unobservable firm-level effects. We find that return on assets drops significantly during the project initiation year. According to fixed effects results, the performance and productivity measures improve in a decreasing manner after project initiation, suggesting that BPR indeed positively affects firm performance on average. We also find that enterprise-wide BPR projects are associated with more negative returns during project initiation than functionally focused projects. However, there is no clear evidence regarding their superiority over functionally focused BPR projects in terms of performance improvements after project initiation, perhaps because grand projects are risky and sometimes lead to grand failures.

Bundling e-banking services

At the same time, AT&T is breaking up again and has made public statements that one-stopshopping is not for everyone. There are some local companies such as net.world (see www.ndw.com) and many others belonging to clec.com (see www.clec.com) buying services from the telecommunication companies and offering to mediumand small-size companies services such as local and/or long-distance phone, Internet connectivity, cable service, or wireless telecommunication. Clec.com is a business space site acting like a portal mentioned in [6.] Usually Competitive Local Exchange Carrier (CLEC) companies, through a Web interface, offer these services in bundles. Such Web sites allow users to examine their usage patterns and choose the optimal bundle that fits their company profile. A similar phenomenon is occurring in the banking industry. Banks and brokerage houses are merging services, such as Firstar and U.S. Bancorp, and FleetBoston and Summit Bank, with Fleet selling both banking and brokerage services through its Quick & Reilly brokerage unit. Another firm, Microcell Telecommunication Inc. has teamed up with Royal Bank of Canada to offer wireless transactional banking services such as bill payments, balances, last transactions, transfers, exchange rates, and prime rates, using Fido’s smart-card technology. Citibank, a unit of Citigroup Inc. will enter Israel’s retail banking market in the second quarter of 2001. Citibank, which has been offering corporate clients commercial and investment-banking services with sister company Salomon Smith Barney, is planning to buy a local bank in Israel to better serve customers. Schwab is another company joining those offering bankerage (banking and brokerage) services as onestop-shopping. Schwab.com offers many services listed on their Web site [5] in bundles, reflecting alliances between Schwab and its partners. The economics literature studies bundles of two items under pure and mixed strategy, focusing on either offering only the bundle or both the bundle Bundling E-Banking Services

Optimization of multi-feeder (depot) printed circuit board manufacturing with error guarantees

This paper considers an integrated optimization problem enhancing productivity in printed circuit board (PCB) manufacturing. The problems of assigning component types to feeder locations and sequencing component placements on the PCB are simultaneously formulated in a mathematical model. Our model differs from earlier studies by allowing component types to be placed in multiple feeders. Although such flexibility adds complexity to the original problem, we develop an integrated solution that has promising results. We develop an integrated algorithm that finds the optimal solution when the optimal solutions for the multi-depot vehicle routing problem (MDVRP) are given. Otherwise, given an e-approximation algorithm for the MDVRP, our integrated solution has a theoretical e-error guarantee for PCB problem. The effectiveness of the integrated approach is shown with extensive computational experiments. � 2002 Elsevier Science B.V. All rights reserved.

Diffusion Models for B2B, B2C, and P2P Exchanges and E-Speak

Consulting groups are predicting that the future of business-to-business (B2B) and business-to-consumer (B2C) exchanges will generate exponentially increasing revenues. However, the economic uncertainties in the market and technological innovations, such as peer-to-peer (P2P) networks and e-Speak from Hewlett Packard, may significantly alter the outlook for the current exchanges. In this study, we adopted a diffusion model for B2B, B2C, and P2P exchanges and e-Speak to capture the future revenue potentials of these electronic exchanges. We simulated the proposed model to incorporate possible market uncertainties. We initially analyzed the case where B2B and B2C increased exponentially. Then, we considered the case of migration from B2B and B2C to P2P and e-Speak. We tested the rate of diffusion with respect to certain parameters, such as imitation, innovation, market potential, and switching rate. With the set of parameters we used, we found out that the effect of imitation was stronger than innovation. The switching rate played an important role in how easy it was for agents to move to later technologies. The inertia factor determined the winner in the marketplace, based on the values, making it more expensive or less expensive to switch to later technologies.