S. Voss

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Papers by S. Voss

An Exact Algorithm for the Reliability Redundancy Allocation Problem

by Marco Caserta and S. Voss

The redundancy allocation problem is the problem of finding the optimal allocation of redundant c... more The redundancy allocation problem is the problem of finding the optimal allocation of redundant components subject to a set of resource constraints. The problem studied in this paper refers to a series-parallel system configuration and allows for component mixing. We propose a new modeling approach, in which the problem is transformed into a multiple choice knapsack problem and solved to optimality via a branch and cut algorithm. The algorithm is tested on well-known sets of benchmark instances. All instances have been solved to optimality in milliseconds or very few seconds on a normal workstation.

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A corridor method based hybrid algorithm for redundancy allocation

by Marco Caserta and S. Voss

In this paper a hybrid algorithm for the redundancy allocation problem is presented. The problem ... more In this paper a hybrid algorithm for the redundancy allocation problem
is presented. The problem is the allocation of redundant components within series-parallel systems. We present an algorithm that deals with the classical formulation, where at least one component per subsystem must be included in the final configuration, as well as the k-out-of-n formulation, in which at least k components per subsystem must be included in the final network configuration. We propose a three-phase scheme in which the cross entropy method, the corridor method and a dynamic programming-based scheme are effectively intertwined. Computational results on well-known benchmark instances as well as on randomly generated large scale instances are presented, proving the effectiveness and robustness of the proposed algorithm.

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A Discrete-Binary Transformation of the Reliability Redundancy Allocation Problem

by Marco Caserta and S. Voss

Given a reliability redundancy optimization problem in its discrete version, it is possible to tr... more Given a reliability redundancy optimization problem in its discrete version, it is possible to transform such integer problem into a corresponding binary problem in log-time. A simple discrete-binary transformation is presented in this paper. The proposed transformation is illustrated using an example taken from the reliability literature. An immediate implication is that a standard exact dynamic programming approach may easily solve instances to optimality that were usually only solved heuristically.

format_quoteThe DP approach's complexity grows with the multiplicative constraints' products, indicating scalability challenges in higher constraint scenarios.format_quote

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A mathematical formulation and complexity considerations for the blocks relocation problem

by Marco Caserta and S. Voss

The blocks relocation problem (BRP) may be defined as follows: given a set of homogeneous blocks ... more The blocks relocation problem (BRP) may be defined as follows: given a set of homogeneous blocks stored in a two-dimensional stock, which relocations are necessary to retrieve the blocks from the stock in a pre-defined order while minimizing the number of those relocations? In this paper, we first prove NP-hardness of the BRP as well as a special case, closing open research questions. Moreover, we propose different solution approaches. First, a mathematical model is presented that provides optimal solutions to the general BRP in cases where instances are small. To overcome such limitation, some realistic assumption taken from the literature is introduced, leading to the definition of a binary linear programming model. In terms of computational time, this approach is reasonably fast to be used to solve medium-sized instances. In addition, we propose a simple heuristic based upon a set of relocation rules. This heuristic is used to generate ''good'' quality solutions for larger instances in very short computational time, and, consequently, is proposed for tackling problem instances where solutions are required (almost) immediately. Solution quality of the heuristic is measured against optimal solutions obtained using a state-of-the-art commercial solver and both of them are compared with reference results from literature.

format_quoteAuthors provide the first mathematically rigorous formulation of the blocks relocation problem (BRP) and prove its NP-hardness.format_quote

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An exact algorithm for the reliability redundancy allocation problem

by Marco Caserta and S. Voss

Multiple choice knapsack problem Branch and cut a b s t r a c t The redundancy allocation problem... more Multiple choice knapsack problem Branch and cut a b s t r a c t The redundancy allocation problem is the problem of finding an optimal allocation of redundant components subject to a set of resource constraints. The problem studied in this paper refers to a series-parallel system configuration and allows for component mixing. We propose a new modeling/solution approach, in which the problem is transformed into a multiple choice knapsack problem and solved to optimality via a branch and cut algorithm. The algorithm is tested on well-known sets of benchmark instances. All instances have been solved to optimality in milliseconds or very few seconds on a normal workstation.

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Design and evaluation of road pricing: state-of-the-art and methodological advances

by Theodore Tsekeris and S. Voss

This article provides an in-depth review of the state-of-the-art and describes methodological adv... more This article provides an in-depth review of the state-of-the-art and describes methodological advances in the design and evaluation of road network pricing schemes. A number of paradigm shifts from the two polar cases of the marginal social cost pricing of road traffic congestion and revenue-maximizing road toll pricing are analyzed, as induced by the need to address realistic design complexities and constraints. The crucial role of the joint consideration of pricing strategies with optimal capacity provision and several network management measures is manifested and an integrated evaluation framework is suggested to incorporate a wide range of road pricing impacts into the scheme design process.

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Teaching meta-heuristics within virtual learning environments

International Transactions in Operational Research, 2004

Modern education of operations research and management science (OR/MS) can greatly benefit from i... more Modern education of operations research and management science (OR/MS) can greatly benefit from interactive learning methods in order to build and develop modeling and problem-solving skills. In this paper we consider the teaching of meta-heuristics as an important part of OR/MS with significant recent interest. We discuss possibilities of supporting the teaching of meta-heuristics such as simulated annealing or tabu search through interactive learning. The paper also presents a survey of some relevant issues within VORMS (Virtual Operations Research/Management Science), a project currently undertaken at six universities within Germany, and provides a presentation of the advances regarding the teaching of metaheuristics within this project. Further ideas refer to incorporating HOTFRAME, a heuristic optimization framework, into the virtual learning environment.

format_quoteThe VORMS project aims to increase learner motivation and integration of operations research methods across various fields through innovative didactical methods.format_quote

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Neigborhood Selection in Variable Neighborhood Search

by Marc Sevaux and S. Voss

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