International audienceWe propose a new algorithm for the classical problem of computing the diameter of undirected unweighted graphs, namely, the maximum distance among all the pairs of nodes, where the distance of a pair of nodes is the number of edges contained in the shortest path connecting these two nodes. Although its worst-case complexity is O(nm) time, where n is the number of nodes and m is the number of edges of the graph, we experimentally show that our algorithm works in O(m) time in practice, requiring few breadth-first searches to complete its task on almost 200 real-world graphs

We consider the on-line channel assignment problem in the case of cellular networks and we formalize this problem as an on-line load balancing problem for temporary tasks with restricted assignment. For the latter problem, we provide a general solution (denoted as the cluster algorithm) and we characterize its competitive ratio in terms of the combinatorial properties of the graph representing the network. We then compare the cluster algorithm with the greedy one when applied to the channel assignment problem: it turns out that the competitive ratio of the cluster algorithm is strictly better than the competitive ratio of the greedy algorithm. The cluster method is general enough to be applied to other on-line load balancing problems and, for some topologies, it can be proved to be optimal. (C) 2003 Elsevier B.V. All rights reserved

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Online education supported by digital courseware will radically alter higher education in ways that we cannot predict. New technologies such as MOOCs and Khan Academy have generated interest in new models for knowledge delivery. The nature of Computer Science content provides special opportunities for computer-supported delivery in both traditional and online classes. Traditional CS textbooks are likely to be replaced by online materials that tightly integrate content with visualizations and automatically assessed exercises. We refer to these new textbook-like artifacts as icseBooks (pronounced "ice books"), for interactive computer science electronic books. IcseBook technology will in turn impact the pedagogy used in CS courses. This report surveys the state of the field, addresses new use cases for CS pedagogy with icseBooks, and lays out a series of research questions for future study.

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In this paper we investigate the problem of computing optimal\ud lottery schemes. From a computational complexity point of view, we\ud prove that the variation of this problem in which the sets to be\ud covered are specified in the input is $\log\ud |\mathcal{T}|$-approximable (where $\mathcal{T}$ denotes the\ud collection of sets to be covered) and it cannot be approximated\ud within a factor smaller than $\log |\mathcal{T}|$, unless\ud $\DP=\NP$. From a combinatorial point of view, we propose\ud new constructions based on the combination of the partitioning\ud technique and of known results regarding the construction of sets\ud of coverings: By means of this combination we will be able to\ud improve several upper bounds on the cardinality of optimal lottery\ud schemes

Abstract.We study the connectivity properties of a family of random graphs which closely model the Bluetooth's device discovery process, where each device tries to connect to other devices within its visibility range in order to establish reliable communication channels yielding a connected topology. Specifically, we provide both analytical and experimental evidence that when the visibility range of each node (i.e., device) is limited to a vanishing function of n, the total number of nodes in the system, full connectivity can still be achieved with high probability by letting each node connect only to a "small" number of visible neighbors. Our results extend previous studies, where connectivity properties were analyzed only for the case of a constant visibility range, and provide evidence that Bluetooth can indeed be used for establishing large ad hoc networks.

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