Results 1  10
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12
Approximation Algorithms for Connected Dominating Sets
 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 ..."
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Cited by 277 (9 self)
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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 ...
Greedy strikes back: Improved facility location algorithms
 Journal of Algorithms
, 1999
"... A fundamental facility location problem is to choose the location of facilities, such as industrial plants and warehouses, to minimize the cost of satisfying the demand for some commodity. There are associated costs for locating the facilities, as well as transportation costs for distributing the co ..."
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Cited by 182 (12 self)
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A fundamental facility location problem is to choose the location of facilities, such as industrial plants and warehouses, to minimize the cost of satisfying the demand for some commodity. There are associated costs for locating the facilities, as well as transportation costs for distributing the commodities. We assume that the transportation costs form a metric. This problem is commonly referred to as the uncapacitated facility location (UFL) problem. Applications to bank account location and clustering, as well as many related pieces of work, are discussed by Cornuejols, Nemhauser and Wolsey [2]. Recently, the first constant factor approximation algorithm for this problem was obtained by Shmoys, Tardos and Aardal [16]. We show that a simple greedy heuristic combined with the algorithm by Shmoys, Tardos and Aardal, can be used to obtain an approximation guarantee of 2.408. We discuss a few variants of the problem, demonstrating better approximation factors for restricted versions of the problem. We also show that the problem is Max SNPhard. However, the inapproximability constants derived from the Max SNP hardness are very close to one. By relating this problem to Set Cover, we prove a lower bound of 1.463 on the best possible approximation ratio assuming NP / ∈ DT IME[n O(log log n)]. 1
Approximation Algorithms for Directed Steiner Problems
 Journal of Algorithms
, 1998
"... We give the first nontrivial 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 ..."
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Cited by 143 (8 self)
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We give the first nontrivial 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 quasipolynomial 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...
Improved Approximation Algorithms for Capacitated Facility Location Problems
"... In a surprising result, Korupolu, Plaxton, and Rajaraman [13] showed that a simple local search heuristic for the capacitated facility location problem (CFLP) in which the service costs obey the triangle inequality produces a solution in polynomial time which is within a factor of 8+ # of the val ..."
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Cited by 79 (1 self)
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In a surprising result, Korupolu, Plaxton, and Rajaraman [13] showed that a simple local search heuristic for the capacitated facility location problem (CFLP) in which the service costs obey the triangle inequality produces a solution in polynomial time which is within a factor of 8+ # of the value of an optimal solution. By simplifying their analysis, we are able to show that the same heuristic produces a solution which is within a factor of 6(1 + #) of the value of an optimal solution. Our simplified analysis uses the supermodularity of the cost function of the problem and the integrality of the transshipment polyhedron. Additionally
Improved Methods for Approximating Node Weighted Steiner Trees and Connected Dominating Sets
 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 approximation ra ..."
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Cited by 68 (1 self)
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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 \branchspiders", 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 01 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. 1.
Rounding via Trees: Deterministic Approximation Algorithms for Group Steiner Trees and kmedian
 In Proceedings of the 30th Annual ACM Symposium on Theory of Computing
, 1998
"... Most optimization problems on an undirected graph reduce in complexity when restricted to instances on a tree. A recent result [3] for probabilistically approximating graph metrics by trees such that no edge stretches (in an expected sense) by more than a factor of O(log 2 n) has resulted in several ..."
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Cited by 56 (8 self)
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Most optimization problems on an undirected graph reduce in complexity when restricted to instances on a tree. A recent result [3] for probabilistically approximating graph metrics by trees such that no edge stretches (in an expected sense) by more than a factor of O(log 2 n) has resulted in several approximation algorithms which exploit the ease of solving problems on trees. The tree construction in [3] is inherently randomized and a natural question to ask is whether approximation algorithms which use this construction can be derandomized. We present a general framework for derandomizing approximation algorithms which use the above tree construction as a primitive. Let \Pi be a graph optimization problem which can be expressed as an integer program with 01 variables ¯ x(e) for each edge and with an objective function expressible as...
Designing Networks with Bounded Pairwise Distance
"... We study the following network design problem: Given a communication network, find a minimum cost subset of missing links such that adding these links to the network makes every pair of points within distance at most d from each other. Theproblemhasbeenstudied earlier[17]undertheassumptionthatallli ..."
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Cited by 49 (0 self)
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We study the following network design problem: Given a communication network, find a minimum cost subset of missing links such that adding these links to the network makes every pair of points within distance at most d from each other. Theproblemhasbeenstudied earlier[17]undertheassumptionthatalllinkcostsas wellaslinklengthsareidentical,andwasshowntobe (logn)hardforeveryd4. Wepresentanovellinearprogrammingbasedapproachtoobtainan O(lognlogd)approximationalgorithmforthecaseofuniform linklengthsandcosts. We alsoextendthe(logn)hardnesstod2f2;3g. On the otherhand,iflinkcostscanvary, weshowthattheproblemis(2log1�n)hardford3. Thisversionofour problemcanbeviewedasaspecialcaseoftheminimum cost dspannerproblemandthusourhardnessresultappliesthereaswell. Ford=2,however,weshowthatthe problemcontinuestobeO(logn)approximablebygivingan O(logn)approximationtothemoregeneralminimumcost2spannerproblem.An(2log1�n)hardness resultalsoholdswhenalllinkcostsareidenticalbutlink lengthsmayvary(appliesevenwhenalllengthsare1or
Scheduling for ReMove and other partially connected architectures
, 2001
"... From a hardware point of view it is beneficial to design microprocessors with as few communication resources as possible. Unfortunately it is hard for compilers to generate code for machines in which the communication network is not fully connected. The three main problems are the selection of units ..."
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Cited by 3 (0 self)
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From a hardware point of view it is beneficial to design microprocessors with as few communication resources as possible. Unfortunately it is hard for compilers to generate code for machines in which the communication network is not fully connected. The three main problems are the selection of units and registers for operations and variables, the routing of the variable paths from the producing operation to the consuming operations, and avoiding deadlocks caused by overcharging the transport resources. The last problem is the hardest in practice.
Local Detection and Recovery from MultiFailure Patterns in MPLSTE Networks
"... Abstract — MPLS Fast Reroute advocates local protection mechanisms to rapidly reroute traffic onto precomputed and signaled bypass tunnels. When the network is subject to multiple element failures, it becomes challenging to handle all the possible failure scenarios, for they are more disruptive and ..."
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Cited by 1 (0 self)
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Abstract — MPLS Fast Reroute advocates local protection mechanisms to rapidly reroute traffic onto precomputed and signaled bypass tunnels. When the network is subject to multiple element failures, it becomes challenging to handle all the possible failure scenarios, for they are more disruptive and may require many more bypass tunnels to be dealt with. The objective of this paper is to adapt the MPLS local recovery schemes to deal with multifailure scenarios, while retaining as much as possible the simplicity and the fast failure detection feature of current (single failure) local recovery mechanisms. This objective is achieved by optimally grouping failure patterns into clusters and minimizing the overall additional network resources — i.e., bypass tunnels and bidirectional forwarding detection sessions — while yielding full recovery from such failure patterns. I.
Approximation Algorithm for Security Games with Costly Resources
"... Abstract. In recent years, algorithms for computing gametheoretic solutions have been developed for realworld security domains. These games are between a defender, who must allocate her resources to defend potential targets, and an attacker, who chooses a target to attack. Existing work has assume ..."
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Cited by 1 (0 self)
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Abstract. In recent years, algorithms for computing gametheoretic solutions have been developed for realworld security domains. These games are between a defender, who must allocate her resources to defend potential targets, and an attacker, who chooses a target to attack. Existing work has assumed the set of defender’s resources to be fixed. This assumption precludes the effective use of approximation algorithms, since a slight change in the defender’s allocation strategy can result in a massive change in her utility. In contrast, we consider a model where resources are obtained at a cost, initiating the study of the following optimization problem: Minimize the total cost of the purchased resources, given that every target has to be defended with at least a certain probability. We give an efficient logarithmic approximation algorithm for this problem. 1