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1.
Given a graph G=(V,E) and a positive integer D , we consider the problem of finding a minimum number of new edges E' such that the augmented graph G'=(V,E\cup E') is biconnected and has diameter no greater than D. In this note we show that this problem is NP-hard for all fixed D , by employing a reduction from the DOMINATING SET problem. We prove that the problem remains NP-hard even for forests and
trees, but in this case we present approximation algorithms with worst-case bounds 3 (for even D ) and 6 (for odd D ). A closely related problem of finding a minimum number of edges such that the augmented graph has diameter no greater than
D has been shown to be NP-hard by Schoone et al. [21] when D=3 , and by Li et al. [17] when D=2.
Received April 19, 1999; revised June 5, 2001. 相似文献
2.
We study the application of the geographic nearest neighbor approach to two problems. The first problem is the construction of an approximately minimum length rectilinear Steiner tree for a set ofn points in the plane. For this problem, we introduce a variation of a subgraph of sizeO(n) used by YaO [31] for constructing minimum spanning trees. Using this subgraph, we improve the running times of the heuristics discussed by Bern [6] fromO(n
2
log
n) toO(n log2
n). The second problem is the construction of a rectilinear minimum spanning tree for a set ofn noncrossing line segments in the plane. We present an optimalO(n logn) algorithm for this problem. The rectilinear minimum spanning tree for a set of points can thus be computed optimally without using the Voronoi diagram. This algorithm can also be extended to obtain a rectilinear minimum spanning tree for a set of nonintersecting simple polygons.The results in this paper are a part of Y. C. Yee's Ph.D. thesis done at SUNY at Albany. He was supported in part by NSF Grants IRI-8703430 and CCR-8805782. S. S. Ravi was supported in part by NSF Grants DCI-86-03318 and CCR-89-05296. 相似文献
3.
杨文海 《网络安全技术与应用》2014,(11):69-70
在交换网络环境中,物理环路可以提高网络的冗余,但容易产生双向的广播环,甚至形成广播风暴,使交换机瘫痪;通过生成树协议生成根网桥,根端口,指定端口和阻塞端口,在逻辑上断开该网段,形成一个无环网络,使网络中无法产生广播环和广播风暴;当其它链路出现故障时,阻塞的端口自动恢复,逻辑断开的线路又被连通,继续传输数据。 相似文献
4.
Takeshi Masuda 《Computer Vision and Image Understanding》2009,113(11):1158-1169
We propose a method for coarse registration of multiple range images that uses a log-polar height map (LPHM) as the key for establishing correspondence. The LPHM is a local height map orthogonally mapped on the tangent plane with the log-polar coordinate system. The input range images are roughly represented by signed distance field (SDF) samples. For each SDF sample, an LPHM is generated and is converted to an invariant feature vector. Point correspondence is established by a nearest neighbor search in feature space. The RANSAC algorithm is applied on the corresponding point pairs between each pair of range images, and the pairwise registration of input range images is determined by the extracted inlier point pairs. Finally, the global registration is determined by constructing a view tree, which is the spanning tree that maximizes the total number of inlier point pairs. The result of coarse registration is used as the initial state of the fine registration and modeling. The proposed method was tested on multiple real range image datasets. 相似文献
5.
6.
M. Hajiaghaei-Keshteli S. Molla-Alizadeh-Zavardehi R. Tavakkoli-Moghaddam 《Computers & Industrial Engineering》2010
In this paper, we consider the fixed-charge transportation problem (FCTP) in which a fixed cost, sometimes called a setup cost, is incurred if another related variable assumes a nonzero value. To tackle such an NP-hard problem, there are several genetic algorithms based on spanning tree and Prüfer number representation. Contrary to the findings in previous works, considering the genetic algorithm (GA) based on spanning tree, we present a pioneer method to design a chromosome that does not need a repairing procedure for feasibility, i.e. all the produced chromosomes are feasible. Also, we correct the procedure provided in previous works, which designs transportation tree with feasible chromosomes. We show the previous procedure does not produce any transportation tree in some situations. Besides, some new crossover and mutation operators are developed and used in this work. Due to the significant role of crossover and mutation operators on the algorithm’s quality, the operators and parameters need to be accurately calibrated to ensure the best performance. For this purpose, various problem sizes are generated at random and then a robust calibration is applied to the parameters using the Taguchi method. In addition, two problems with different sizes are solved to evaluate the performance of the presented algorithm and to compare that performance with LINGO and also with the solution presented in previous work. 相似文献
7.
8.
9.
10.
This paper deals with compact label-based representations for trees. Consider an n-node undirected connected graph G with a predefined numbering on the ports of each node. The all-ports tree labeling ℒ
all
gives each node v of G a label containing the port numbers of all the tree edges incident to v. The upward tree labeling ℒ
up
labels each node v by the number of the port leading from v to its parent in the tree. Our measure of interest is the worst case and total length of the labels used by the scheme, denoted
M
up
(T) and S
up
(T) for ℒ
up
and M
all
(T) and S
all
(T) for ℒ
all
. The problem studied in this paper is the following: Given a graph G and a predefined port labeling for it, with the ports of each node v numbered by 0,…,deg (v)−1, select a rooted spanning tree for G minimizing (one of) these measures. We show that the problem is polynomial for M
up
(T), S
up
(T) and S
all
(T) but NP-hard for M
all
(T) (even for 3-regular planar graphs). We show that for every graph G and port labeling there exists a spanning tree T for which S
up
(T)=O(nlog log n). We give a tight bound of O(n) in the cases of complete graphs with arbitrary labeling and arbitrary graphs with symmetric port labeling. We conclude by
discussing some applications for our tree representation schemes.
A preliminary version of this paper has appeared in the proceedings of the 7th International Workshop on Distributed Computing
(IWDC), Kharagpur, India, December 27–30, 2005, as part of Cohen, R. et al.: Labeling schemes for tree representation. In:
Proceedings of 7th International Workshop on Distributed Computing (IWDC), Lecture Notes of Computer Science, vol. 3741, pp. 13–24
(2005).
R. Cohen supported by the Pacific Theaters Foundation.
P. Fraigniaud and D. Ilcinkas supported by the project “PairAPair” of the ACI Masses de Données, the project “Fragile” of
the ACI Sécurité et Informatique, and by the project “Grand Large” of INRIA.
A. Korman supported in part by an Aly Kaufman fellowship.
D. Peleg supported in part by a grant from the Israel Science Foundation. 相似文献