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91.
For a mixed hypergraph
, where
and
are set systems over the vertex set X, a coloring is a partition of X into ‘color classes’ such that every
meets some class in more than one vertex, and every
has a nonempty intersection with at least two classes. The feasible set of
, denoted
, is the set of integers k such that
admits a coloring with precisely k nonempty color classes. It was proved by Jiang et al. [Graphs and Combinatorics 18 (2002), 309–318] that a set S of natural numbers is the feasible set of some mixed hypergraph if and only if either
or S is an ‘interval’
for some integer k ≥ 1.
In this note we consider r-uniform mixed hypergraphs, i.e. those with |C| = |D| = r for all
and all
, r ≥ 3. We prove that S is the feasible set of some r-uniform mixed hypergraph with at least one edge if and only if either
for some natural number k ≥ r − 1, or S is of the form
where S′′ is any (possibly empty) subset of
and S′ is either the empty set or {r − 1} or an ‘interval’ {k, k + 1, ..., r − 1} for some k, 2 ≤ k ≤ r − 2. We also prove that all these feasible sets
can be obtained under the restriction
, i.e. within the class of ‘bi-hypergraphs’.
Research supported in part by the Hungarian Scientific Research Fund, OTKA grant T-049613. 相似文献
92.
图G(V,E)的一个k-正常全染色f叫做一个k-点强全染色当且仅当对任意v∈V(G), N[v]中的元素被染不同色,其中N[v]={u|uv∈V(G)}∪{v}.χTvs(G)=min{k|存在图G的k- 点强全染色}叫做图G的点强全色数.对3-连通平面图G(V,E),如果删去面fo边界上的所有点后的图为一个树图,则G(V,E)叫做一个Halin-图.本文确定了最大度不小于6的Halin- 图和一些特殊图的的点强全色数XTvs(G),并提出了如下猜想:设G(V,E)为每一连通分支的阶不小于6的图,则χTvs(G)≤△(G) 2,其中△(G)为图G(V,E)的最大度. 相似文献
93.
颜色传递是获得夜视图像自然彩色的一种方法,以红外和微光图像为研究对象,提出了一种基于颜色传递和目标增强的夜视图像彩色融合方法。首先结合红外和微光图像各自的特点,采用TNO法生成伪彩色融合图像(目标图像),很好地保留了图像的细节信息,然后选取一幅相近的参考图像,把目标图像和参考图像转换到YCbCr颜色空间进行各个通道一阶(均值)和二阶(标准差)统计量匹配的颜色传递,同时在Cr通道引入一个对比度增强因子来增强图像中的兴趣目标。实验结果表明,文中方法不仅使得夜视图像获得了如白天参考图像般自然、真实的色彩,而且提高了图像的细节,目标也更加突出,更有利于观察者对场景的理解。 相似文献
94.
95.
对|V(G)|≥3的连通图G,若κ-正常边染色法满足相邻点的色集合不相同,则称该染色法为κ-邻强边染色,其最小的κ称为图G的邻强边色数。张忠辅等学者猜想:对|V(G)|≥3的连通图G,G≠C_5其邻强边色数至多为△(G)+2,利用组合分析的方法给出了完全图的广义Mycielski图的邻强边色数,从而验证了图的邻强边染色猜想对于此类图成立。 相似文献
96.
97.
This note presents improved approximation guarantees for the requirement cut problem: given an n-vertex edge-weighted graph G=(V,E), and g groups of vertices X1,…,Xg⊆V with each group Xi having a requirement ri between 0 and |Xi|, the goal is to find a minimum cost set of edges whose removal separates each group Xi into at least ri disconnected components. We give a tight Θ(logg) approximation ratio for this problem when the underlying graph is a tree, and show how this implies an O(logk⋅logg) approximation ratio for general graphs, where . 相似文献
98.
Let be a plane graph with the sets of vertices, edges, and faces V, E, and F, respectively. If one can color all elements in using k colors so that any two adjacent or incident elements receive distinct colors, then G is said to be entirely k‐colorable. Kronk and Mitchem [Discrete Math 5 (1973) 253‐260] conjectured that every plane graph with maximum degree Δ is entirely ‐colorable. This conjecture has now been settled in Wang and Zhu (J Combin Theory Ser B 101 (2011) 490–501), where the authors asked: is every simple plane graph entirely ‐colorable? In this article, we prove that every simple plane graph with is entirely ‐colorable, and conjecture that every simple plane graph, except the tetrahedron, is entirely ‐colorable. 相似文献
99.
This paper studies an interference coordination method by means of spectrum allocation in Long-Term Evolution (LTE) multi-cell scenario that comprises of macrocells and femtocells. The purpose is to maximize the total throughput of femtocells while ensuring the Signal-to-Interference plus Noise Ratio (SINR) of the edge macro mobile stations (mMSs) and the edge femtocell Mobile Stations (fMSs). A new spectrum allocation algorithm based on graph theory is proposed to reduce the interference. Firstly, the ratio of Resource Blocks (RBs) that mMSs occupy is obtained by genetic algorithm. Then, after considering the impact of the macro Base Stations (mBSs) and small scale fading to the fMS on different RBs, multi-interference graphs are established and the spectrum is allocated dynamically. The simulation results show that the proposed algorithm can meet the Quality of Service (QoS) requirements of the mMSs. It can strike a balance between the edge fMSs’ throughput and the whole fMSs’ throughput. 相似文献
100.