Valter Boljunčić

Combinatorial optimization issues in scheduling

This special issue of the Journal of Scheduling is devoted to the ECCO XXI Conference, the 21st Annual Meeting of the European Chapter on Combinatorial Optimization, which was held at the facilities of the University of Dubrovnik (Croatia) from May 29 to May 31, 2008. In 1991 ECCO had planned to have its annual meeting in Dubrovnik, but the event had to be canceled due to the unstable political situation in Croatia at that time. ECCO, the Working Group of the European Chapter on Combinatorial Optimization, was created in 1987 by Catherine Roucairol, Dominique de Werra, and Alexander Rinnooy Kan. Through the years, the group has provided an opportunity to discuss novelties in important areas of combinatorial optimization. The group, which has more than 1,000 members, is open to everybody interested in the field, either

Location Problems in Telecommunications

Location optimization is an important problem in design and usage of telecommunication networks. In different forms it appears in wire-based and in wireless networks, during unicast and multicast usage, in static, as well as in dynamic, networks. We provide an application oriented survey of recent results in location optimization pertaining to telecommunications networks, addressing problems such as converter, splitter, and amplifier placement in wavelength division multiplex (WDM) optical networks, concentrator location in designing access/backbone networks, base station location in Universal Mobile Telecommunication System (UMTS), and location management in mobile (cellular and ad hoc) networks.

A note on robustness of the efficient DMUs in data envelopment analysis

Sensitivity analysis of extreme efficient DMUs was studied by Zhu (J. Zhu, EOR(90)(3)(1996)451-460) using the modified CCR (A. Charnes, W.W. Cooper, E. Rhodes, EOR 2(1978)429-444)model. Upward proportional variations of inputs and downward proportional variations of outputs were considered. The procedure suggested by Zhu is a new approach to sensitivity analysis and can result in sufficient and necessary conditions on the changes which do not alter the efficiency of DMUs. However, in certain instances the results presented by Zhu do not hold. The aim of this note is to poin out shortcomings which can be met following procedure proposed by Zhu. This includes inefficieny of so-called projected points, domination of obtained hyperplane, case of simultaneous changes of inputs and outputs, and case of infeasibility even if all data are greater than 0.

Sensitivity analysis in the additive model of data envelopment analysis

Sensitivity analysis of the optimal solutions of data envelopment analysis is illustrated here by a numerical example.

On delay versus congestion in designing rearrangeable multihop lightwave networks

We investigate design issues of optical networks in light of two conflicting criteria: throughput maximization (or equivalently, congestion minimization) versus delay minimization. We assume the network has an arbitrary topology, the flow can be split and sent via different routes, and it can be transferred via intermediate nodes. Tabu search heuristic is used to compare solutions with different weights assigned to each of the two criteria. The approach is tested on a benchmark data set, the 14-dimensional NSFNET T1 network with traffic from 1993. The results suggest that: (1) some connectivity matrices are quite robust and desirable regarding both criteria simultaneously; (2) forcing minimization of total delay unconditionally can result in significantly inferior throughput. Some decision strategies are outlined.