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排序方式: 共有411条查询结果,搜索用时 250 毫秒
21.
22.
Stochastic scenario trees are a new and popular method by which surveillance systems can be analyzed to demonstrate freedom from pests and disease. For multiple component systems—such as a combination of a serological survey and systematically collected observations—it can be difficult to represent the complete system in a tree because many branches are required to represent complex conditional relationships. Here we show that many of the branches of some scenario trees have identical outcomes and are therefore redundant. We demonstrate how to prune branches and derive compact representations of scenario trees using matrix algebra and Bayesian belief networks. The Bayesian network representation is particularly useful for calculation and exposition. It therefore provides a firm basis for arguing disease freedom in international forums. 相似文献
23.
Franklin Dexter 《统计学通讯:模拟与计算》2013,42(3):879-886
A test for homogeneity of several populations against the simple tree alternative is proposed when the observations in various groups are subject to the same pattern of random right-censorship. The test is a generalization of the one proposed by Slivka (1970) which is useful when testing time is expensive so that an early termination of an experiment is desirable. The power of the test is examined in a simulation study. 相似文献
24.
Ram C. Tiwari 《统计学通讯:理论与方法》2013,42(2):625-642
In this paper, a nonparametric Bayesian approach to the analysis of binary response data is considered. Using a Dirichlet process prior, and squared error loss, the Bayes estimators of response probabilities are obtained. Finally, the results obtained are employed to analyze the ARC 090 Trial data. 相似文献
25.
Gabriel Chandler Leif T. Johnson 《Journal of Statistical Computation and Simulation》2013,83(2):384-401
Tree-based methods similar to CART have recently been utilized for problems in which the main goal is to estimate some set of interest. It is often the case that the boundary of the true set is smooth in some sense, however tree-based estimates will not be smooth, as they will be a union of ‘boxes’. We propose a general methodology for smoothing such sets that allows for varying levels of smoothness on the boundary automatically. The method is similar to the idea underlying support vector machines, which is applying a computationally simple technique to data after a non-linear mapping to produce smooth estimates in the original space. In particular, we consider the problem of level-set estimation for regression functions and the dyadic tree-based method of Willett and Nowak [Minimax optimal level-set estimation, IEEE Trans. Image Process. 16 (2007), pp. 2965–2979]. 相似文献
26.
We investigate the computational complexity of two special cases of the Steiner tree problem where the distance matrix is a Kalmanson matrix or a circulant matrix, respectively. For Kalmanson matrices we develop an efficient polynomial time algorithm that is based on dynamic programming. For circulant matrices we give an
-hardness proof and thus establish computational intractability. 相似文献
27.
Leszek Gasieniec Jesper Jansson Andrzej Lingas Anna Östlin 《Journal of Combinatorial Optimization》1999,3(2-3):183-197
In this paper we study a few important tree optimization problems with applications to computational biology. These problems ask for trees that are consistent with an as large part of the given data as possible. We show that the maximum homeomorphic agreement subtree problem cannot be approximated within a factor of
, where N is the input size, for any 0
in polynomial time unless P = NP, even if all the given trees are of height 2. On the other hand, we present an O(N log N)-time heuristic for the restriction of this problem to instances with O(1) trees of height O(1) yielding solutions within a constant factor of the optimum. We prove that the maximum inferred consensus tree problem is NP-complete, and provide a simple, fast heuristic for it yielding solutions within one third of the optimum. We also present a more specialized polynomial-time heuristic for the maximum inferred local consensus tree problem. 相似文献
28.
This paper proposes an optimization model and shows that most inverse combinatorial optimization problems so far discussed can be fit into this model as special cases. We propose a Newton-type algorithm for this model under l
norm. This algorithm can solve the model in strongly polynomial time if the subproblem involved is solvable in strongly polynomial time for any fixed value of the parameter appearing in the subproblem, and it is shown that most particular inverse optimization problems encountered are this kind. Therefore, through this paper we show that a large group of inverse optimization problems can be handled in a uniform way and solved in strongly polynomial time. 相似文献
29.
Yoshiyuki Kusakari Daisuke Masubuchi Takao Nishizeki 《Journal of Combinatorial Optimization》2001,5(2):249-266
Let G = (V,E) be a plane graph with nonnegative edge weights, and let
be a family of k vertex sets
, called nets. Then a noncrossing Steiner forest for
in G is a set
of k trees
in G such that each tree
connects all vertices, called terminals, in net N
i, any two trees in
do not cross each other, and the sum of edge weights of all trees is minimum. In this paper we give an algorithm to find a noncrossing Steiner forest in a plane graph G for the case where all terminals in nets lie on any two of the face boundaries of G. The algorithm takes time
if G has n vertices and each net contains a bounded number of terminals. 相似文献
30.
"编译原理"课程的教学探索 总被引:5,自引:0,他引:5
姚雪梅 《重庆交通学院学报(社会科学版)》2003,3(2):85-86
"编译原理"课程由于其理论难度及目前本科学生中普遍存在的各种思想误区,造成难以取得理想的教学效果.针对这一现状,从如何提高学习热情,利用形象化教学手段使抽象理论具体化,合理组织实验及课程设计内容等方面入手,提出了相应对策. 相似文献