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41.
本文讨论了树映射f的链等价集的性质,得到了f具有零拓扑熵的几个等价条件,并证明了:如果 f的一个链等价集是个无限集,那么这个链等价集的任何孤立点都是f的非周期的终于周期点. 相似文献
42.
The constrained forest problem seeks a minimum-weight spanning forest in an undirected edge-weighted graph such that each tree spans at least a specified number of vertices. We present a greedy heuristic for this NP-hard problem, whose solutions are at least as good as, and often better than, those produced by the best-known 2-approximate heuristic. 相似文献
43.
G. Tinhofer 《Mathematical Programming》1984,28(3):337-348
A graphsack problem is a certain binary linear optimization problem with applications in optimal network design. From there
a rational graphsack problem is derived by allowing the variables to vary continuously between 0 and 1. In this paper we deal
with rational graphsack problems. First we develop the concept of compressed solutions and the concept of augmenting cuts.
Making use of these concepts a very simple optimality criterion is derived. Finally an efficient algorithm solving rational
graphsack problems is given which is polynomially bounded in time and which is closely related to the simplex algorithm. 相似文献
44.
一阶数≥3的简单连通图叫做1-Hamilton连通的,若对每一对顶点v_1、v_2及任一边v_2v_3(v_1≠v_3),存在连接v_1和v_2,并且经过v_3v_2的Hamilton路.本文中我们证明:连通图的树图或是1-Hamilton连通的,或为一超立方体,或同构于K_2×K_3和W_5之一. 相似文献
45.
On the core and nucleolus of minimum cost spanning tree games 总被引:1,自引:0,他引:1
We develop two efficient procedures for generating cost allocation vectors in the core of a minimum cost spanning tree (m.c.s.t.)
game. The first procedure requires O(n
2) elementary operations to obtain each additional point in the core, wheren is the number of users. The efficiency of the second procedure, which is a natural strengthening of the first procedure,
stems from the special structure of minimum excess coalitions in the core of an m.c.s.t. game. This special structure is later
used (i) to ease the computational difficulty in computing the nucleolus of an m.c.s.t. game, and (ii) to provide a geometric
characterization for the nucleolus of an m.c.s.t. game. This geometric characterization implies that in an m.c.s.t. game the
nucleolus is the unique point in the intersection of the core and the kernel. We further develop an efficient procedure for
generating fair cost allocations which, in some instances, coincide with the nucleolus. Finally, we show that by employing
Sterns' transfer scheme we can generate a sequence of cost vectors which converges to the nucleolus.
Part of this research was done while the author was visiting the Department of Operations Research at Stanford University.
This research was partially supported by Natural Sciences and Engineering Research Council Canada Grant A-4181. 相似文献
46.
Let be a set of at least two vertices in a graph . A subtree of is a -Steiner tree if . Two -Steiner trees and are edge-disjoint (resp. internally vertex-disjoint) if (resp. and ). Let (resp. ) be the maximum number of edge-disjoint (resp. internally vertex-disjoint) -Steiner trees in , and let (resp. ) be the minimum (resp. ) for ranges over all -subset of . Kriesell conjectured that if for any , then . He proved that the conjecture holds for . In this paper, we give a short proof of Kriesell’s Conjecture for , and also show that (resp. ) if (resp. ) in , where . Moreover, we also study the relation between and , where is the line graph of . 相似文献
47.
Michael D. Barrus 《Discrete Mathematics》2010,310(20):2600-2612
A card of a graph G is a subgraph formed by deleting one vertex. The Reconstruction Conjecture states that each graph with at least three vertices is determined by its multiset of cards. A dacard specifies the degree of the deleted vertex along with the card. The degree-associated reconstruction number drn(G) is the minimum number of dacards that determine G. We show that drn(G)=2 for almost all graphs and determine when drn(G)=1. For k-regular n-vertex graphs, drn(G)≤min{k+2,n−k+1}. For vertex-transitive graphs (not complete or edgeless), we show that drn(G)≥3, give a sufficient condition for equality, and construct examples with large drn. Our most difficult result is that drn(G)=2 for all caterpillars except stars and one 6-vertex example. We conjecture that drn(G)≤2 for all but finitely many trees. 相似文献
48.
49.
Oxygen and carbon isotopic compositions of tree ring cellulose (δ13Ccell and δ18Ocell) were measured for pines growing at four sites in east Germany. Three sites differed markedly in soil water availability within a short distance and the fourth site served as a reference. The choice of the sites was guided by the desire to detect effects of air pollution on the long-term trend of isotopic compositions and to examine the influence of soil water availability on the relationship between the carbon and oxygen isotope ratios. Locations in east Germany are particularly well suited for the study of pollution effects because there was a steady increase in environmental contamination until the German Reunification in 1990, followed by a sharp decline due to the implementation of stricter environmental standards. The long-term trend of δ13Ccell showed an extraordinary increase in the period 1945–1990 and a rapid decrease after 1990, whereas δ18Ocell remained nearly constant. The increase of δ13Ccell is explained by secondary fractionation caused by phytotoxicity of SO2. Two effects are mainly responsible for the secondary fractionation under SO2 exposure: increase of dark respiration, and changes in photosynthate allocation and partitioning. Both effects do not influence δ18Ocell. Furthermore, a significant positive correlation between the year-to-year variations of carbon and oxygen isotope ratios (δ13Cresid and δ18Oresid) has been found for all sites. The slopes of the relationship between δ13Cresid and δ18Oresid differ insignificantly. It is concluded that this relationship is not influenced by soil water availability but by climatic variables. 相似文献