Showing papers by "Madhav V. Marathe published in 1996"
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TL;DR: In this paper, the authors considered the problem of finding a tree of minimum weight spanning at least k nodes in an edge-weighted graph and showed that the problem is NP-hard even for points in the Euclidean plane.
Abstract: We study the problem of finding small trees. Classical network design problems are considered with the additional constraint that only a specified number $k$ of nodes are required to be connected in the solution. A prototypical example is the $k$MST problem in which we require a tree of minimum weight spanning at least $k$ nodes in an edge-weighted graph. We show that the $k$MST problem is NP-hard even for points in the Euclidean plane. We provide approximation algorithms with performance ratio $2\sqrt{k}$ for the general edge-weighted case and $O(k^{1/4})$ for the case of points in the plane. Polynomial-time exact solutions are also presented for the class of treewidth-bounded graphs, which includes trees, series-parallel graphs, and bounded bandwidth graphs, and for points on the boundary of a convex region in the Euclidean plane.
We also investigate the problem of finding short trees and, more generally, that of finding networks with minimum diameter. A simple technique is used to provide a polynomial-time solution for finding $k$-trees of minimum diameter. We identify easy and hard problems arising in finding short networks using a framework due to T. C. Hu.
135 citations
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TL;DR: A heuristic for the domatic partition problem with a performance ratio of 4.5 and on-line minimum vertex coloring, which guarantees a solution which is within a factor of 2 of the optimal (off-line) value.
15 citations
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03 Jul 1996
TL;DR: In this paper, the authors focus on the problem of finding a low-cost network, under one cost function, that services every node in the graph, under another cost function (i.e., every node of the graph is within a specified distance from the network).
Abstract: Several practical instances of network design problems often require the network to satisfy multiple constraints. In this paper, we focus on the following problem (and its variants): find a low-cost network, under one cost function, that services every node in the graph, under another cost function, (i.e., every node of the graph is within a prespecified distance from the network). This study has important applications to the problems of optical network design and the efficient maintenance of distributed databases.
14 citations
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12 Jun 1996TL;DR: The problem of computing optimal reduction strategy for modifying the network as above in NP-hard is considered and the first polynomial time approximation algorithms for the problem are presented, where the cost functions C{sub e} are allowed to be taken from a broad class of functions.
Abstract: We consider the problem of reducing the edge lengths of a given network so that the modified network has a spanning tree of small total length. It is assumed that each edge e of the given network has an associated function c e that specifies the cost of shortening the edge by a given amount and that there is a budget B on the total reduction cost. The goal is to develop a reduction strategy satisfying the budget constraint so that the total length of a minimum spanning tree in the modified network is the smallest possible over all reduction strategies that obey the budget constraint.
13 citations
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TL;DR: This paper aims to find a low-cost network that services every node in the graph, under another cost function, (i.e., every node of the graph is within a prespecified distance from the network).
Abstract: Several practical instances of network design problems often require the network to satisfy multiple constraints. In this paper, we focus on the following problem (and its variants): find a low-cost network, under one cost function, that services every node in the graph, under another cost function, (i.e., every node of the graph is Within a prespecified distance from the network). Such problems find applications in optical network design and the efficient maintenance of distributed databases.We utilize the framework developed in Marathe et al. [1995] co formulate these problems as bicriteria network design problems, and present approximation algorithms for a class of service-constrained network design problems. We also present lower bounds on the approximability of these problems that demonstrate that our performance ratios are close to best possible.
5 citations
01 Jan 1996
TL;DR: In this paper, the problem of finding the maximum number of non-overlapping occurrences of the pattern in the text was introduced and polynomial time approximation algorithms and approximation schemes for this problem were devised.
Abstract: We introduce the following optimization version of the classical pattern matching problem (referred to as the maximum pattern matching problem). Given a two-dimensional rectangular text and a two-dimensional rectangular pattern, find the maximum number of non-overlapping occurrences of the pattern in the text. Unlike the classical two-dimensional pattern matching problem, the maximum two-dimensional pattern matching problem is NP-complete. We devise polynomial time approximation algorithms and approximation schemes for this problem. We also briefly discuss how the approximation algorithms can be extended to include a number of other variants of the problem.
5 citations
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02 Jul 1996
TL;DR: It is shown that in general the problem of computing optimal reduction strategy for modifying the network as above is {bold NP}-hard.
Abstract: We study {ital budget constrained optimal network upgrading problems}. Such problems aim at finding optimal strategies for improving a network under some cost measure subject to certain budget constraints. Given an edge weighted graph {ital G(V,E)}, in the {ital edge based upgrading model}, it is assumed that each edge {ital e} of the given network has an associated function {ital c(e)} that specifies for each edge {ital e} the amount by which the length {ital l(e)} is to be reduced. In the {ital node based upgrading model} a node {ital v} can be upgraded at an expense of cost {ital (v)}. Such an upgrade reduces the cost of each edge incident on {ital v} by a fixed factor {rho}, where 0 < {rho} < 1. For a given budget, {ital B}, the goal is to find an improvement strategy such that the total cost of reduction is a most the given budget {ital B} and the cost of a subgraph (e.g. minimum spanning tree) under the modified edge lengths is the best over all possible strategies which obey the budget constraint. Define an ({alpha},{beta})-approximation algorithm as a polynomial-time algorithm that produces a solution within {alpha} times the optimal function value, violating the budget constraint by a factor of at most {Beta}. The results obtained in this paper include the following 1. We show that in general the problem of computing optimal reduction strategy for modifying the network as above is {bold NP}-hard. 2. In the node based model, we show how to devise a near optimal strategy for improving the bottleneck spanning tree. The algorithms have a performance guarantee of (2 ln {ital n}, 1). 3. for the edge based improvement problems we present improved (in terms of performance and time) approximation algorithms. 4. We also present pseudo-polynomial time algorithms (extendible to polynomial time approximation schemes) for a number of edge/node based improvement problems when restricted to the class of treewidth-bounded graphs.
2 citations
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01 Sep 1996
TL;DR: The authors present the first polynomial time approximation algorithms for the problem of finding a minimum cost set of nodes to be upgraded so that the resulting network has a spanning tree in which edge is of delay at most a given value {delta}.
Abstract: Consider a network where nodes represent processors and edges represent bidirectional communication links. The processor at a node v can be upgraded at an expense of cost(v). Such an upgrade reduces the delay of each link emanating from v by a fixed factor x, where 0 < x < 1. The goal is to find a minimum cost set of nodes to be upgraded so that the resulting network has a spanning tree in which edge is of delay at most a given value {delta}. The authors provide both hardness and approximation results for the problem. They show that the problem is NP-hard and cannot be approximated within any factor {beta} < ln n, unless NP {improper_subset} DTIME(n{sup log log n}), where n is the number of nodes in the network. They then present the first polynomial time approximation algorithms for the problem. For the general case, the approximation algorithm comes within a factor of 2 ln n of the minimum upgrading cost. When the cost of upgrading each node is 1, they present an approximation algorithm with a performance guarantee of 4(2 + ln {Delta}), where {Delta} is the maximum node degree. Finally, they present a polynomial time algorithm for the class of treewidth-bounded graphs.
1 citations
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10 Jun 1996TL;DR: This work introduces the following optimization version of the classical pattern matching problem: Given a two-dimensional rectangular text and a 2- dimensional rectangular pattern find the maximum number of non-overlapping occurrences of the the pattern in the text.
Abstract: We introduce the following optimization version of the classical pattern matching problem (referred to as the maximum pattern matching problem). Given a two-dimensional rectangular text and a 2-dimensional rectangular pattern find the maximum number of non-overlapping occurrences of the the pattern in the text.