Papers by Vangelis Th. Paschos
European Journal of Operational Research - EJOR, 2006
AIP Conference Proceedings, 2002
Revue française de gestion, 2007
Le passage de l'approvisionnement synchrone à la production synchrone constitue une alternative a... more Le passage de l'approvisionnement synchrone à la production synchrone constitue une alternative aux configurations logistiques de proximité souvent utilisées dans les chaînes logistiques orientées vers la production de masse de produits fortement diversifiés et devant satisfaire très rapidement les clients, comme c'est le cas dans l'industrie automobile. Cette transformation offre de nouveaux degrés de liberté susceptibles, sous certaines conditions, d'apporter des gains d'efficience. Figer plus tôt certaines décisions accroît le risque de divergence entre prévision et réalisation. De nouveaux mécanismes correcteurs doivent être imaginés. On s'attache ici à identifier ces transformations et leurs conséquences pour les partenaires de la chaîne logistique, en s'appuyant sur le concept de point de pénétration de commande qui facilite l'analyse de l'interdépendance.
Physical Review Letters, 2004
Decision Support Systems, 2005
Cet article présente la modélisation d'une perturbation sur un réseau de transport. Le modèle pro... more Cet article présente la modélisation d'une perturbation sur un réseau de transport. Le modèle proposé doit assurer la synthèse, l'évaluation et la mise à jour des informations disponibles afin de faciliter la tâche de l'opérateur assurant la surveillance du réseau. Pour atteindre cet objectif, nous proposons une modélisation formelle du concept de perturbation. Cette modélisation permet de capitaliser les connaissances disponibles au sein d'un poste de contrôle et d'assurer le suivi du processus en temps réel. Nous proposons également une représentation multi-agent d'un incident permettant l'intégration du traitement d'une perturbation au sein de l'activité d'un réseau de transport.
Discrete Mathematics & Theoretical Computer Science
A mixed dominating set is a collection of vertices and edges that dominates all vertices and edge... more A mixed dominating set is a collection of vertices and edges that dominates all vertices and edges of a graph. We study the complexity of exact and parameterized algorithms for \textsc{Mixed Dominating Set}, resolving some open questions. In particular, we settle the problem's complexity parameterized by treewidth and pathwidth by giving an algorithm running in time $O^*(5^{tw})$ (improving the current best $O^*(6^{tw})$), as well as a lower bound showing that our algorithm cannot be improved under the Strong Exponential Time Hypothesis (SETH), even if parameterized by pathwidth (improving a lower bound of $O^*((2 - \varepsilon)^{pw})$). Furthermore, by using a simple but so far overlooked observation on the structure of minimal solutions, we obtain branching algorithms which improve both the best known FPT algorithm for this problem, from $O^*(4.172^k)$ to $O^*(3.510^k)$, and the best known exponential-time exact algorithm, from $O^*(2^n)$ and exponential space, to $O^*(1.912^n...
Discrete Applied Mathematics, 2018
In (k, r)-Center we are given a (possibly edge-weighted) graph and are asked to select at most k ... more In (k, r)-Center we are given a (possibly edge-weighted) graph and are asked to select at most k vertices (centers), so that all other vertices are at distance at most r from a center. In this paper we provide a number of tight fine-grained bounds on the complexity of this problem with respect to various standard graph parameters. Specifically: • For any r ≥ 1, we show an algorithm that solves the problem in O * ((3r + 1) cw) time, where cw is the clique-width of the input graph, as well as a tight SETH lower bound matching this algorithm's performance. As a corollary, for r = 1, this closes the gap that previously existed on the complexity of Dominating Set parameterized by cw. • We strengthen previously known FPT lower bounds, by showing that (k, r)-Center is W[1]-hard parameterized by the input graph's vertex cover (if edge weights are allowed), or feedback vertex set, even if k is an additional parameter. Our reductions imply tight ETH-based lower bounds. Finally, we devise an algorithm parameterized by vertex cover for unweighted graphs. • We show that the complexity of the problem parameterized by tree-depth is 2 Θ(td 2) , by showing an algorithm of this complexity and a tight ETH-based lower bound. We complement these mostly negative results by providing FPT approximation schemes parameterized by clique-width or treewidth, which work efficiently independently of the values of k, r. In particular, we give algorithms which, for any > 0, run in time O * ((tw/) O(tw)), O * ((cw/) O(cw)) and return a (k, (1 +)r)-center if a (k, r)-center exists, thus circumventing the problem's W-hardness.
Computing and …, Jan 1, 2004
Lecture Notes in Computer Science, 2013
ABSTRACT We present a natural wireless sensor network problem, which we model as a probabilistic ... more ABSTRACT We present a natural wireless sensor network problem, which we model as a probabilistic version of the min dominating set problem. We show that this problem, being a generalization of the classical min dominating set, is NP-hard, even in bipartite graphs. We first study the complexity of probabilistic min dominating set in graphs where min dominating set is polynomial, mainly in trees and paths and then we give some approximation results for it.
European Journal of Operational Research, 1995
We present a new research domain in Operational Research, probabilistic combinatorial optimizatio... more We present a new research domain in Operational Research, probabilistic combinatorial optimization problems. We survey and comment a number of results, and we discuss several problems dealing with this domain as well as future research issues.
Lecture Notes in Computer Science, 2008
We study a robustness model for graph-problems under vertex-uncertainty. We assume that any verte... more We study a robustness model for graph-problems under vertex-uncertainty. We assume that any vertex v i of the input-graph G(V, E) has only a probability p i to be present in the final graph to be optimized (i.e., the final instance for the problem tackled will be only a sub-graph of the initial graph). Under this model, the original "deterministic" problem gives rise to a new (deterministic) problem on the same input-graph G, having the same set of feasible solutions as the former one, but its objective function can be very different from the original one, the set of its optimal solutions too. Moreover, this objective function is a sum of 2 |V | terms; hence, its computation is not immediately polynomial. We give sufficient conditions for large classes of graph-problems under which objective functions of the robust counterparts are polynomially computable and optimal solutions are well-characterized. Finally, we apply these general results to natural and well-known representatives of any of the classes considered.
Journal of Combinatorial Optimization, 2009
We revisit in this paper the probabilistic coloring problem ( ) and focus ou... more We revisit in this paper the probabilistic coloring problem ( ) and focus ourselves on bipartite and split graphs. We first give some general properties dealing with the optimal solution. We then show that the unique 2-coloring achieves approximation ratio 2 in bipartite graphs under any system of vertex-probabilities and propose a polynomial algorithm achieving tight approximation ratio 8/7 under identical vertex-probabilities. Then we deal with restricted cases of bipartite graphs. Main results for these cases are the following. Under non-identical vertex-probabilities - is polynomial for stars, for trees with bounded degree and a fixed number of distinct vertex-probabilities, and, consequently, also for paths with a fixed number of distinct vertex-probabilities. Under identical vertex-probabilities, is polynomial for paths, for even and odd cycles and for trees whose leaves are either at even or at odd levels. Next, we deal with split graphs and show that is NP-hard, even under identical vertex-probabilities. Finally, we study approximation in split graphs and provide a 2-approximation algorithm for the case of distinct probabilities and a polynomial time approximation schema under identical vertex-probabilities.
Annals of Operations Research, 1997
The satellite shot sequencing problem consists in choosing the pictures to be completed by defini... more The satellite shot sequencing problem consists in choosing the pictures to be completed by defining sequences of shots which must respect technical constraints and limits. We propose a graph-theoretic model for both the medium- and the short-term sequencing and present algorithmic solutions by using properties of the model.
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Papers by Vangelis Th. Paschos