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排序方式: 共有848条查询结果,搜索用时 46 毫秒
41.
Spiros A. Argyros 《Proceedings of the American Mathematical Society》2001,129(11):3231-3239
It is shown that every separable Banach space universal for the class of reflexive Hereditarily Indecomposable space contains isomorphically and hence it is universal for all separable spaces. This result shows the large variety of reflexive H.I. spaces.
42.
Hans H. Brungs Joachim Grä ter 《Transactions of the American Mathematical Society》2000,352(7):3357-3379
A subring of a division algebra is called a valuation ring of if or holds for all nonzero in . The set of all valuation rings of is a partially ordered set with respect to inclusion, having as its maximal element. As a graph is a rooted tree (called the valuation tree of ), and in contrast to the commutative case, may have finitely many but more than one vertices. This paper is mainly concerned with the question of whether each finite, rooted tree can be realized as a valuation tree of a division algebra , and one main result here is a positive answer to this question where can be chosen as a quaternion division algebra over a commutative field.
43.
T. S. Evans 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,56(1):65-69
Evolving networks with a constant number of edges may be
modelled using a rewiring process. These models are used to
describe many real-world processes including the evolution of
cultural artifacts such as family names, the evolution of gene
variations, and the popularity of strategies in simple
econophysics models such as the minority game. The model is
closely related to Urn models used for glasses, quantum gravity
and wealth distributions. The full mean field equation for the
degree distribution is found and its exact solution and generating
solution are given. 相似文献
44.
Zhongzhi Zhang Shuigeng Zhou Lichao Chen Jihong Guan Lujun Fang Yichao Zhang 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,59(1):99-107
We propose a geometric growth model for weighted
scale-free networks, which is controlled by two tunable parameters.
We derive exactly the main characteristics of the networks, which
are partially determined by the parameters. Analytical results
indicate that the resulting networks have power-law distributions of
degree, strength, weight and betweenness, a scale-free behavior for
degree correlations, logarithmic small average path length and
diameter with network size. The obtained properties are in agreement
with empirical data observed in many real-life networks, which shows
that the presented model may provide valuable insight into the real
systems. 相似文献
45.
Inevitable self-similar topology of binary trees and their diverse hierarchical density 总被引:1,自引:0,他引:1
K. Paik P. Kumar 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,60(2):247-258
Self-similar topology, which can be characterized
as power law size distribution, has been found in diverse tree
networks ranging from river networks to taxonomic trees. In this
study, we find that the statistical self-similar topology is an
inevitable consequence of any full binary tree organization. We show
this by coding a binary tree as a unique bifurcation string. This
coding scheme allows us to investigate trees over the realm from
deterministic to entirely random trees. To obtain partial random
trees, partial random perturbation is added to the deterministic
trees by an operator similar to that used in genetic algorithms. Our
analysis shows that the hierarchical density of binary trees is more
diverse than has been described in earlier studies. We find that the
connectivity structure of river networks is far from strict
self-similar trees. On the other hand, organization of some social
networks is close to deterministic supercritical trees. 相似文献
46.
47.
The range searching problem is a fundamental problem in computational geometry, with numerous important applications. Most research has focused on solving this problem exactly, but lower bounds show that if linear space is assumed, the problem cannot be solved in polylogarithmic time, except for the case of orthogonal ranges. In this paper we show that if one is willing to allow approximate ranges, then it is possible to do much better. In particular, given a bounded range Q of diameter w and >0, an approximate range query treats the range as a fuzzy object, meaning that points lying within distance w of the boundary of Q either may or may not be counted. We show that in any fixed dimension d, a set of n points in
can be preprocessed in O(n+logn) time and O(n) space, such that approximate queries can be answered in O(logn(1/)d) time. The only assumption we make about ranges is that the intersection of a range and a d-dimensional cube can be answered in constant time (depending on dimension). For convex ranges, we tighten this to O(logn+(1/)d−1) time. We also present a lower bound for approximate range searching based on partition trees of Ω(logn+(1/)d−1), which implies optimality for convex ranges (assuming fixed dimensions). Finally, we give empirical evidence showing that allowing small relative errors can significantly improve query execution times. 相似文献
48.
Fuzzy classifier identification using decision tree and multiobjective evolutionary algorithms 总被引:3,自引:0,他引:3
This paper presents a hybrid method for identification of Pareto-optimal fuzzy classifiers (FCs). In contrast to many existing methods, the initial population for multiobjective evolutionary algorithms (MOEAs) is neither created randomly nor a priori knowledge is required. Instead, it is created by the proposed two-step initialization method. First, a decision tree (DT) created by C4.5 algorithm is transformed into an FC. Therefore, relevant variables are selected and initial partition of input space is performed. Then, the rest of the population is created by randomly replacing some parameters of the initial FC, such that, the initial population is widely spread. That improves the convergence of MOEAs into the correct Pareto front. The initial population is optimized by NSGA-II algorithm and a set of Pareto-optimal FCs representing the trade-off between accuracy and interpretability is obtained. The method does not require any a priori knowledge of the number of fuzzy sets, distribution of fuzzy sets or the number of relevant variables. They are all determined by it. Performance of the obtained FCs is validated by six benchmark data sets from the literature. The obtained results are compared to a recently published paper [H. Ishibuchi, Y. Nojima, Analysis of interpretability-accuracy tradeoff of fuzzy systems by multiobjective fuzzy genetics-based machine learning, International Journal of Approximate Reasoning 44 (1) (2007) 4–31] and the benefits of our method are clearly shown. 相似文献
49.
Here we investigate a majorization problem involving starlike function of complex order belonging to a certain class defined by means of fractional derivatives. Relevant connections of the main results obtained in this paper with those given by earlier workers on the subject are also pointed out. 相似文献
50.
Donatella Merlini 《Discrete Applied Mathematics》2008,156(5):627-646
We find the generating function counting the total internal path length of any proper generating tree. This function is expressed in terms of the functions (d(t),h(t)) defining the associated proper Riordan array. This result is important in the theory of Riordan arrays and has several combinatorial interpretations. 相似文献