Results 1 - 10 of 138

Approximation Algorithms for Connected Dominating Sets

by Sudipto Guha, Samir Khuller - Algorithmica , 1996
"... The dominating set problem in graphs asks for a minimum size subset of vertices with the following property: each vertex is required to either be in the dominating set, or adjacent to some node in the dominating set. We focus on the question of finding a connected dominating set of minimum size, whe ..."
Abstract - Cited by 366 (9 self) - Add to MetaCart
The dominating set problem in graphs asks for a minimum size subset of vertices with the following property: each vertex is required to either be in the dominating set, or adjacent to some node in the dominating set. We focus on the question of finding a connected dominating set of minimum size, where the graph induced by vertices in the dominating set is required to be connected as well. This problem arises in network testing, as well as in wireless communication. Two polynomial time algorithms that achieve approximation factors of O(H (\Delta)) are presented, where \Delta is the maximum degree, and H is the harmonic function. This question also arises in relation to the traveling tourist problem, where one is looking for the shortest tour such that each vertex is either visited, or has at least one of its neighbors visited. We study a generalization of the problem when the vertices have weights, and give an algorithm which achieves a performance ratio of 3 ln n. We also consider the ...
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When trees collide: An approximation algorithm for the generalized Steiner problem on networks

by Ajit Agrawal, Philip Klein, R. Ravi , 1994
"... We give the first approximation algorithm for the generalized network Steiner problem, a problem in network design. An instance consists of a network with link-costs and, for each pair fi; jg of nodes, an edge-connectivity requirement r ij . The goal is to find a minimum-cost network using the a ..."
Abstract - Cited by 249 (38 self) - Add to MetaCart
We give the first approximation algorithm for the generalized network Steiner problem, a problem in network design. An instance consists of a network with link-costs and, for each pair fi; jg of nodes, an edge-connectivity requirement r ij . The goal is to find a minimum-cost network using the available links and satisfying the requirements. Our algorithm outputs a solution whose cost is within 2dlog 2 (r + 1)e of optimal, where r is the highest requirement value. In the course of proving the performance guarantee, we prove a combinatorial min-max approximate equality relating minimum-cost networks to maximum packings of certain kinds of cuts. As a consequence of the proof of this theorem, we obtain an approximation algorithm for optimally packing these cuts; we show that this algorithm has application to estimating the reliability of a probabilistic network.

Geometric Shortest Paths and Network Optimization

by Joseph S.B. Mitchell - Handbook of Computational Geometry , 1998
"... Introduction A natural and well-studied problem in algorithmic graph theory and network optimization is that of computing a "shortest path" between two nodes, s and t, in a graph whose edges have "weights" associated with them, and we consider the "length" of a path to ..."
Abstract - Cited by 187 (15 self) - Add to MetaCart
Introduction A natural and well-studied problem in algorithmic graph theory and network optimization is that of computing a "shortest path" between two nodes, s and t, in a graph whose edges have "weights" associated with them, and we consider the "length" of a path to be the sum of the weights of the edges that comprise it. Efficient algorithms are well known for this problem, as briefly summarized below. The shortest path problem takes on a new dimension when considered in a geometric domain. In contrast to graphs, where the encoding of edges is explicit, a geometric instance of a shortest path problem is usually specified by giving geometric objects that implicitly encode the graph and its edge weights. Our goal in devising efficient geometric algorithms is generally to avoid explicit construction of the entire underlying graph, since the full induced graph may be very large (even exponential in the input size, or infinite). Computing an optimal
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Approximation Algorithms for Directed Steiner Problems

by Moses Charikar, Chandra Chekuri, To-yat Cheung, Zuo Dai, Ashish Goel, Sudipto Guha, Ming Li - Journal of Algorithms , 1998
"... We give the first non-trivial approximation algorithms for the Steiner tree problem and the generalized Steiner network problem on general directed graphs. These problems have several applications in network design and multicast routing. For both problems, the best ratios known before our work we ..."
Abstract - Cited by 178 (8 self) - Add to MetaCart
We give the first non-trivial approximation algorithms for the Steiner tree problem and the generalized Steiner network problem on general directed graphs. These problems have several applications in network design and multicast routing. For both problems, the best ratios known before our work were the trivial O(k)-approximations. For the directed Steiner tree problem, we design a family of algorithms that achieves an approximation ratio of i(i \Gamma 1)k 1=i in time O(n i k 2i ) for any fixed i ? 1, where k is the number of terminals. Thus, an O(k ffl ) approximation ratio can be achieved in polynomial time for any fixed ffl ? 0. Setting i = log k, we obtain an O(log 2 k) approximation ratio in quasi-polynomial time. For the directed generalized Steiner network problem, we give an algorithm that achieves an approximation ratio of O(k 2=3 log 1=3 k), where k is the number of pairs of vertices that are to be connected. Related problems including the group Steiner...
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A polylogarithmic approximation algorithm for the group Steiner tree problem

by Naveen Garg, Goran Konjevod, R. Ravi - Journal of Algorithms , 2000
"... The group Steiner tree problem is a generalization of the Steiner tree problem where we ae given several subsets (groups) of vertices in a weighted graph, and the goal is to find a minimum-weight connected subgraph containing at least one vertex from each group. The problem was introduced by Reich a ..."
Abstract - Cited by 149 (9 self) - Add to MetaCart
The group Steiner tree problem is a generalization of the Steiner tree problem where we ae given several subsets (groups) of vertices in a weighted graph, and the goal is to find a minimum-weight connected subgraph containing at least one vertex from each group. The problem was introduced by Reich and Widmayer and finds applications in VLSI design. The group Steiner tree problem generalizes the set covering problem, and is therefore at least as had. We give a randomized O(log 3 n log k)-approximation algorithm for the group Steiner tree problem on an n-node graph, where k is the number of groups. The best previous ink)v/ (Bateman, Helvig, performance guarantee was (1 + - Robins and Zelikovsky).
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Improved Methods for Approximating Node Weighted Steiner Trees and Connected Dominating Sets

by Sudipto Guha, Samir Khuller - INFORMATION AND COMPUTATION , 1999
"... A greedy approximation algorithm based on "spider decompositions" was developed by Klein and Ravi for node weighted Steiner trees. This algorithm provides a worst case approximation ratio of 2 ln k, where k is the number of terminals. However, the best known lower bound on the approximatio ..."
Abstract - Cited by 87 (1 self) - Add to MetaCart
A greedy approximation algorithm based on "spider decompositions" was developed by Klein and Ravi for node weighted Steiner trees. This algorithm provides a worst case approximation ratio of 2 ln k, where k is the number of terminals. However, the best known lower bound on the approximation ratio is ln k, assuming that NP 6 DT IM E[n O(log log n)], by a reduction from set cover [9, 4]. We show that for the unweighted case we can obtain an approximation factor of ln k. For the weighted case we develop a new decomposition theorem, and generalize the notion of "spiders" to "branch-spiders", that are used to design a new algorithm with a worst case approximation factor of 1:5lnk. This algorithm, although polynomial, is not very practical due to its high running time; since we need to repeatedly nd many minimum weight matchings in each iteration. We are able to generalize the method to yield an approximation factor approaching 1:35 ln k. We also develop a simple greedy algorithm that is practical and has a worst case approximation factor of 1:6103 ln k. The techniques developed for the second algorithm imply a method of approximating node weighted network design problems de ned by 0-1 proper functions. These new ideas also lead to improved approximation guarantees for the problem of nding a minimum node weighted connected dominating set. The previous best approximation guarantee for this problem was 3 ln n [7]. By a direct application of the methods developed in this paper we are able to develop an algorithm with an approximation factor approaching 1:35 ln n.

Approximation Algorithms for Non-Uniform Buy-at-Bulk Network Design

by C. Chekuri, et al. , 2006
"... We consider approximation algorithms for non-uniform buy-at-bulk network design problems. The first nontrivial approximation algorithm for this problem is due to Charikar and Karagiozova (STOC' 05); for an instance on h pairs their algorithm has an approximation guarantee of exp( O(plog h log ..."
Abstract - Cited by 55 (12 self) - Add to MetaCart
We consider approximation algorithms for non-uniform buy-at-bulk network design problems. The first nontrivial approximation algorithm for this problem is due to Charikar and Karagiozova (STOC' 05); for an instance on h pairs their algorithm has an approximation guarantee of exp( O(plog h log log h)) for the uniform-demand case, and log D * exp(O(plog h log log h)) for the general demand case, where D is the total demand. We improve upon this result, by presenting the first poly-logarithmic approximation for this problem. The ratio we obtain is O(log3 h * min{log D, fl(h2)}) where h is the number of pairs and fl(n) is the worst case distortion in embedding the metric induced by a n vertex graph into a distribution over its spanning trees. Using the best known upper bound on fl(n) we obtain an O(min{log3 h*log D, log5 h log log h})ratio approximation. We also give poly-logarithmic approximations for some variants of the singe-source prob-lem that we need for the multicommodity problem.
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Network Lifetime and Power Assignment in Ad-Hoc Wireless Networks

by Gruia Calinescu, Sanjiv Kapoor, Alexander Olshevsky, et al. - IN ESA , 2003
"... Used for topology control in ad-hoc wireless networks, Power Assignment is a family of problems, each defined by a certain connectivity constraint (such as strong connectivity) The input consists of a directed complete weighted graph G = (V; c). The power of a vertex u in a directed spanning subgra ..."
Abstract - Cited by 53 (4 self) - Add to MetaCart
Used for topology control in ad-hoc wireless networks, Power Assignment is a family of problems, each defined by a certain connectivity constraint (such as strong connectivity) The input consists of a directed complete weighted graph G = (V; c). The power of a vertex u in a directed spanning subgraph H is given by pH(u) = maxuv2E(H) c(uv). The power of H is given by p(H) = P u2V pH(u), Power Assignment seeks to minimize p(H) while H satisfies the given connectivity constraint. We

SYMMETRIC CONNECTIVITY WITH MINIMUM POWER CONSUMPTION IN RADIO NETWORKS

by G. Călinescu, I. I. Măndoiu, et al.
"... We study the problem of assigning transmission ranges to the nodes of a multi-hop packet radio network (also known as static ad-hoc wireless network) so as to minimize the total power consumed under the constraint that enough power is provided to the nodes to ensure that the network is connected. Pr ..."
Abstract - Cited by 51 (6 self) - Add to MetaCart
We study the problem of assigning transmission ranges to the nodes of a multi-hop packet radio network (also known as static ad-hoc wireless network) so as to minimize the total power consumed under the constraint that enough power is provided to the nodes to ensure that the network is connected. Precisely, we require that the bidirectional links established by the transmission range of every node form a connected graph. We call this problem Symmetric Min-Power Connectivity. Implicit results in previous papers are the NP-Hardness of Symmetric Min-Power Connectivity, and a very simple 2-approximation algorithm. Using similarity with the Steiner Tree problem, we improve the approximation ratio to 1 + (ln 3)=2 + ffl, and present a practical algorithm with approximation ratio at most 15=8.

A series of approximation algorithms for the Acyclic Directed Steiner Tree problem

by Alexander Zelikovsky - ALGORITHMICA , 1997
"... Given an acyclic directed network, a subset S of nodes (terminals), and a root r, the acyclic directed Steiner tree problem requires a minimum-cost subnetwork which contains paths from r to each terminal. It is known that unless NP ` DT IME[n polylog n] no polynomial-time algorithm can guarantee be ..."
Abstract - Cited by 42 (1 self) - Add to MetaCart
Given an acyclic directed network, a subset S of nodes (terminals), and a root r, the acyclic directed Steiner tree problem requires a minimum-cost subnetwork which contains paths from r to each terminal. It is known that unless NP ` DT IME[n polylog n] no polynomial-time algorithm can guarantee better then (ln k)/4-approximation, where k is the number of terminals. In this paper we give an O(kffl)-approximation algorithm for any ffl? 0. This result improves the previously known k-approximation.
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