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2 Annals of Computer Science and Information Systems

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Algorithmic Handling of Time Expanded Networks

Quilliot Alain, Figueroa Jose-Luis, Toussaint Hélène, Wagler Annegret

Annals of Computer Science and Information Systems

2023

Vol. 35

667--676

Time Expanded Networks, built by considering the nodes of a base network over some time space, are powerful tools for the formulation of problems involving synchronization mechanisms. Those mechanisms may for instance be related to the interaction between resource production and consumption or between routing and scheduling. Still, in most cases, deriving algorithms from those formulations is difficult, due to both the size of resulting network structure and the fact that reducing this size through rounding techniques tends to induce uncontrolled essor propagation. We address here this algorithmic issue, while proposing a generic decomposition scheme which works by first skipping the temporal dimension of the problem and next expanding resulitng projected solution into a full solution of the problem set on the time expanded network.

A novel integer linear programming model for routing and spectrum assignment in optical networks

Hadhbi Youssouf, Kerivin Hervé, Wagler Annegret

Annals of Computer Science and Information Systems

2019

Vol. 18

127--134

The routing and spectrum assignment problem is an NP-hard problem that receives increasing attention during the last years. Existing integer linear programming models for the problem are either very complex and suffer from tractability issues or are simplified and incomplete so that they can optimize only some objective functions. The majority of models uses edge-path formulations where variables are associated with all possible routing paths so that the number of variables grows exponentially with the size of the instance. An alternative is to use edge-node formulations that allow to devise compact models where the number of variables grows only polynomially with the size of the instance. However, all known edge-node formulations are incomplete as their feasible region is a superset of all feasible solutions of the problem and can, thus, handle only some objective functions. Our contribution is to provide the first complete edge-node formulation for the routing and spectrum assignment problem which leads to a tractable integer linear programming model. Indeed, computational results show that our complete model is competitive with incomplete models as we can solve instances of the RSA problem larger than instances known in the literature to optimality within reasonable time and w.r.t. several objective functions. We further devise some directions of future research.