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On the computational complexity of centers locating in a graph

Ján Plesník (1980)

Aplikace matematiky

It is shown that the problem of finding a minimum k -basis, the n -center problem, and the p -median problem are N P -complete even in the case of such communication networks as planar graphs with maximum degree 3. Moreover, a near optimal m -center problem is also N P -complete.

On the hardness of approximating the UET-UCT scheduling problem with hierarchical communications

Evripidis Bampis, R. Giroudeau, J.-C. König (2002)

RAIRO - Operations Research - Recherche Opérationnelle

We consider the unit execution time unit communication time ( UET-UCT ) scheduling model with hierarchical communications [1], and we study the impact of the hierarchical communications hypothesis on the hardness of approximation. We prove that there is no polynomial time approximation algorithm with performance guarantee smaller than 5 / 4 (unless 𝒫 = 𝒩𝒫 ). This result is an extension of the result of Hoogeveen et al. [6] who proved that there is no polynomial time ρ -approximation algorithm with ρ < 7 / 6 for the...

On the hardness of approximating the UET-UCT scheduling problem with hierarchical communications

Evripidis Bampis, R. Giroudeau, J.-C. König (2010)

RAIRO - Operations Research

We consider the unit execution time unit communication time (UET-UCT) scheduling model with hierarchical communica tions [CITE], and we study the impact of the hierarchical communications hypothesis on the hardness of approximation. We prove that there is no polynomial time approximation algorithm with performance guarantee smaller than 5/4 (unless P = NP). This result is an extension of the result of Hoogeveen et al. [CITE] who proved that there is no polynomial time ρ-approximation algorithm...

On the M/G/1 retrial queue subjected to breakdowns

Natalia V. Djellab (2002)

RAIRO - Operations Research - Recherche Opérationnelle

Retrial queueing systems are characterized by the requirement that customers finding the service area busy must join the retrial group and reapply for service at random intervals. This paper deals with the M/G/1 retrial queue subjected to breakdowns. We use its stochastic decomposition property to approximate the model performance in the case of general retrial times.

On the M/G/1 retrial queue subjected to breakdowns

Natalia V. Djellab (2010)

RAIRO - Operations Research

Retrial queueing systems are characterized by the requirement that customers finding the service area busy must join the retrial group and reapply for service at random intervals. This paper deals with the M/G/1 retrial queue subjected to breakdowns. We use its stochastic decomposition property to approximate the model performance in the case of general retrial times.

On the minimum cost multiple-source unsplittable flow problem

Meriema Belaidouni, Walid Ben-Ameur (2007)

RAIRO - Operations Research

The minimum cost multiple-source unsplittable flow problem is studied in this paper. A simple necessary condition to get a solution is proposed. It deals with capacities and demands and can be seen as a generalization of the well-known semi-metric condition for continuous multicommdity flows. A cutting plane algorithm is derived using a superadditive approach. The inequalities considered here are valid for single knapsack constraints. They are based on nondecreasing superadditive functions and...

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