Results 11  20
of
45
Graph Clustering Using Distancek Cliques
 IN PROC. OF GRAPH DRAWING
, 1999
"... Identifying the natural clusters of nodes in a graph and treating them as supernodes or metanodes for a higher level graph (or an abstract graph) is a technique used for the reduction of visual complexity of graphs with a large number of nodes. In this paper we report on the implementation of a clus ..."
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Cited by 14 (1 self)
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Identifying the natural clusters of nodes in a graph and treating them as supernodes or metanodes for a higher level graph (or an abstract graph) is a technique used for the reduction of visual complexity of graphs with a large number of nodes. In this paper we report on the implementation of a clustering algorithm based on the idea of distancek cliques, a generalization of the idea of the cliques in graphs. The performance of the clustering algorithm on some large graphs obtained from the archives of Bell Laboratories is presented.
Automatic Frequency Assignment for Cellular Telephones Using Constraint Satisfaction Techniques
 Proceedings of the Tenth International Conference on Logic Programming
, 1993
"... We study the problem of automatic frequency assignment for cellular telephone systems. The frequency assignment problem is viewed as the problem to minimize the unsatisfied soft constraints in a constraint satisfaction problem (CSP) over a finite domain of frequencies involving cochannel, adjacent ..."
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Cited by 13 (1 self)
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We study the problem of automatic frequency assignment for cellular telephone systems. The frequency assignment problem is viewed as the problem to minimize the unsatisfied soft constraints in a constraint satisfaction problem (CSP) over a finite domain of frequencies involving cochannel, adjacent channel, and cosite constraints. The soft constraints are automatically derived from signal strength prediction data. The CSP is solved using a generalized graph coloring algorithm. Graphtheoretical results play a crucial role in making the problem tractable. Performance results from a realworld frequency assignment problem are presented. We develop the generalized graph coloring algorithm by stepwise refinement, starting from DSATUR and augmenting it with local propagation, constraint lifting, intelligent backtracking, redundancy avoidance, and iterative deepening. Key Words: frequency assignment, constraints, graph coloring, intelligent backtracking, iterative deepening. 1 Introduction...
X.: Minimumlatency aggregation scheduling in multihop wireless networks
 In: ACM MobiHoc
, 2009
"... Minimumlatency aggregation schedule (MLAS) in synchronous multihop wireless networks seeks a shortest schedule for data aggregation subject to the interference constraint. In this paper, we study MLAS under the protocol interference model in which each node has a unit communication radius and an in ..."
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Cited by 13 (3 self)
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Minimumlatency aggregation schedule (MLAS) in synchronous multihop wireless networks seeks a shortest schedule for data aggregation subject to the interference constraint. In this paper, we study MLAS under the protocol interference model in which each node has a unit communication radius and an interference radius ρ ≥ 1. All known aggregation schedules assumed ρ = 1, and the bestknown aggregation latency with ρ = 1 is 23R+∆−18 where R and ∆ are the radius and maximum degree of the communication topology respectively. In this paper, we first construct three aggregations schedules with ρ = 1 of latency 15R + ∆ − 4, 2R + O (log R) + ∆ and 1 + O log R / 3 √ R R + ∆ respectively. Then, we obtain two aggregation schedules with ρ> 1 by expanding the first two aggregation schedules with ρ = 1. Both aggregation schedules with ρ> 1 have latency within constant factors of the minimum aggregation latency.
Automatic Tiling of Iterative Stencil Loops
 ACM TRANSACTIONS ON PROGRAMMING LANGUAGE SYSTEMS
, 2004
"... ... This paper presents a compiler framework for automatic tiling of iterative stencil loops, with the objective of improving the cache performance. The paper first presents a technique which allows loop tiling to satisfy data dependences in spite of the di#culty created by imperfectlynested inner ..."
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Cited by 11 (0 self)
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... This paper presents a compiler framework for automatic tiling of iterative stencil loops, with the objective of improving the cache performance. The paper first presents a technique which allows loop tiling to satisfy data dependences in spite of the di#culty created by imperfectlynested inner loops. It does so by skewing the inner loops over the time steps and by applying a uniform skew factor to all loops at the same nesting level. Based on a memory cost analysis, the paper shows that the skew factor must be minimized at every loop level in order to minimize cache misses. A graphtheoretical algorithm, which takes polynomial time, is presented to determine the minimum skew factor. Furthermore, the memorycost analysis derives the tile size which minimizes capacity misses. Given the tile size, an e#cient and general arraypadding scheme is applied to remove conflict misses. Experiments are conducted on sixteen test programs and preliminary results show an average speedup of 1.58 and a maximum speedup of 5.06 across those test programs
Towards Optimally Multiplexed Applications of Universal DNA Tag Systems
 In Proc. 7th Annual International Conference on Research in Computational Molecular Biology
, 2003
"... We study a design and optimization problem that occurs, for example, when single nucleotide polymorphisms (SNPs) are to be genotyped using a universal DNA tag array. The problem of optimizing the universal array to avoid disruptive crosshybridization between universal components of the system was a ..."
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Cited by 10 (2 self)
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We study a design and optimization problem that occurs, for example, when single nucleotide polymorphisms (SNPs) are to be genotyped using a universal DNA tag array. The problem of optimizing the universal array to avoid disruptive crosshybridization between universal components of the system was addressed in a previous work. However, crosshybridization can also occur assayspecifically, due to unwanted complementarity involving assayspecific components. Here we examine the problem of identifying the most economic experimental configuration of the assayspecific components that avoids crosshybridization. Our formalization translates this problem into the problem of covering the vertices of one side of a bipartite graph by a minimum number of balanced subgraphs of maximum degree 1. We show that the general problem is NPcomplete. However, in the real biological setting the vertices that need to be covered have degrees bounded by d. We exploit this restriction and develop an O(d)approximation algorithm for the problem. We also give an O(d)approximation for a variant of the problem in which the covering subgraphs are required to be vertexdisjoint. In addition, we propose a stochastic model for the input data and use it to prove a lower bound on the cover size. We complement our theoretical analysis by implementing two heuristic approaches and testing their performance on simulated and real SNP data.
Minimumlatency broadcast scheduling in wireless ad hoc networks
 in Proceedings of INFOCOM, 2007
"... Abstract — A wide range of applications for wireless ad hoc networks are timecritical and impose stringent requirement on the communication latency. This paper studies the problem MinimumLatency Broadcast Scheduling (MLBS) in wireless ad hoc networks represented by unitdisk graphs. This problem i ..."
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Cited by 9 (3 self)
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Abstract — A wide range of applications for wireless ad hoc networks are timecritical and impose stringent requirement on the communication latency. This paper studies the problem MinimumLatency Broadcast Scheduling (MLBS) in wireless ad hoc networks represented by unitdisk graphs. This problem is NPhard. A trivial lower bound on the minimum broadcast latency is the radius R of the network with respect to the source of the broadcast, which is the maximum distance of all the nodes from the source of the broadcast. The previously bestknown approximation algorithm for MLBS produces a broadcast schedule with latency at most 648R. Inthispaper,we present three progressively improved approximation algorithms for MLBS. They produce broadcast schedules with latency at most 24R − 23, 16R − 15, andR + O (log R) respectively. I.
OVSFCDMA code assignment for wireless ad hoc networks
 ACM DialM
, 2004
"... Orthogonal Variable Spreading Factor (OVSF) CDMA code consists of an infinite number of codewords with variable rates, in contrast to the conventional orthogonal fixedspreadingfactor CDMA code. Thus, it provides a means of supporting of variable rate data service at low hardware cost. However, assi ..."
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Cited by 6 (3 self)
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Orthogonal Variable Spreading Factor (OVSF) CDMA code consists of an infinite number of codewords with variable rates, in contrast to the conventional orthogonal fixedspreadingfactor CDMA code. Thus, it provides a means of supporting of variable rate data service at low hardware cost. However, assigning OVSFCDMA codes to wireless ad hoc nodes posts a new challenge since not every pair of OVSFCDMA codewords are orthogonal to each other. In an OVSFCDMA wireless ad hoc network, a code assignment has to be conflictfree, i.e., two nodes can be assigned the same codeword or two nonorthogonal codewords if and only if their transmission will not interfere with each other. The throughput (resp., bottleneck) of a code assignment is the sum (resp., minimum) of the rates of the assigned codewords. The maxthroughput (resp., maxbottleneck) conflictfree code assignment problem seeks a conflictfree code assignment which achieves the maximum throughput (resp., bottleneck). In this paper, we present several efficient methods for conflictfree code assignment in OVSFCDMA wireless ad hoc networks. Each method is proved to be either a constantapproximation for maxthroughput conflictfree code assignment problem, or a constantapproximation for maxbottleneck conflictfree code assignment problem, or constantapproximations for both problems simultaneously.
Approximation algorithms for the weighted independent set problem
 IN GRAPHTHEORETIC CONCEPTS IN COMPUTER SCIENCE, 31ST INTERNATIONAL WORKSHOP, WG
, 2005
"... In unweighted case, approximation ratio for the independent set problem has been analyzed in terms of the graph parameters, such as the number of vertices, maximum degree, and average degree. In weighted case, no corresponding results are given for average degree. It is not appropriate that we anal ..."
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Cited by 6 (1 self)
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In unweighted case, approximation ratio for the independent set problem has been analyzed in terms of the graph parameters, such as the number of vertices, maximum degree, and average degree. In weighted case, no corresponding results are given for average degree. It is not appropriate that we analyze weighted independent set algorithms in terms of average degree, since inserting the vertices with small weight decreases average degree arbitrarily without significantly changing approximation ratio. In this paper, we introduce the “weighted ” average degree and “weighted ” inductiveness, and analyze algorithms for the weighted independent set problem in terms of these parameters.
On Crossing Sets, Disjoint Sets and the Pagenumber
, 1998
"... Let G = (V; E) be a tpartite graph with n vertices and m edges, where the partite sets are given. We present an O(n 2 m 1:5 ) time algorithm to construct drawings of G in the plane so that the size of the largest set of pairwise crossing edges, and at the same time, the size of the largest set ..."
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Cited by 6 (0 self)
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Let G = (V; E) be a tpartite graph with n vertices and m edges, where the partite sets are given. We present an O(n 2 m 1:5 ) time algorithm to construct drawings of G in the plane so that the size of the largest set of pairwise crossing edges, and at the same time, the size of the largest set of disjoint (pairwise noncrossing) edges are O( p t \Delta m). As an application we embed G in a book of O( p t \Delta m) pages, in O(n 2 m 1:5 ) time, resolving an open question for the pagenumber problem. A similar result is obtained for the dual of the pagenumber or the queuenumber. Our algorithms are obtained by derandomizing a probabilistic proof. 1 Introduction and Summary 1.1 Preliminaries Throughout this paper G = (V; E) is an undirected graph with jV j = n and jEj = m. A linear ordering of a set S is a bijection from S to f1; 2; : : : ; jSjg. Let h be a linear ordering of V . Consider a drawing of G that is obtained by placing the vertices along a straight line in the pl...
EdgeColoring and fColoring for Various Classes of Graphs
 MATCH Commun. Math. Comput. Chem
, 1999
"... In an ordinary edgecoloring of a graph each color... This paper gives efficient sequential and parallel algorithms to find ordinary edgecolorings and fcolorings for various classes of graphs such as bipartite graphs, planar graphs, and graphs having fixed degeneracy, treewidth, genus, arboricity ..."
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Cited by 5 (0 self)
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In an ordinary edgecoloring of a graph each color... This paper gives efficient sequential and parallel algorithms to find ordinary edgecolorings and fcolorings for various classes of graphs such as bipartite graphs, planar graphs, and graphs having fixed degeneracy, treewidth, genus, arboricity, unicyclic index or thickness.