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An new initialization method for fuzzy c-means algorithm   总被引:1,自引:0,他引:1  
In this paper an initialization method for fuzzy c-means (FCM) algorithm is proposed in order to solve the two problems of clustering performance affected by initial cluster centers and lower computation speed for FCM. Grid and density are needed to extract approximate clustering center from sample space. Then, an initialization method for fuzzy c-means algorithm is proposed by using amount of approximate clustering centers to initialize classification number, and using approximate clustering centers to initialize initial clustering centers. Experiment shows that this method can improve clustering result and shorten clustering time validly.  相似文献
2.
A viral infection model with nonlinear incidence rate and delayed immune response is investigated. It is shown that if the basic reproduction ratio of the virus is less than unity, the infection-free equilibrium is globally asymptotically stable. By analyzing the characteristic equation, the local stability of the chronic infection equilibrium of the system is discussed. Furthermore, the existence of Hopf bifurcations at the chronic infection equilibrium is also studied. By means of an iteration technique, sufficient conditions are obtained for the global attractiveness of the chronic infection equilibrium. Numerical simulations are carried out to illustrate the main results.  相似文献
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探讨具有有限多个风险资产和一个无风险资产、有多个投资者参与的资本资产市场中非负均衡价格的存在性条件与确定问题,从以下角度改进了现有结果:采用期望损失(Expected shortfall,简称ES)作为风险度量,保证了均值-ES框架下所得结果与期望效用极大化原理结果的一致性;对证券收益的联合分布不做假设;考虑了比例交易费用对价格的影响,所得结果更贴近现实的金融市场;不仅给出了非负均衡价格存在唯一的充要条件,而且导出了其具体表达式;在对比分析其与现有结果异同的同时,还讨论了所给充要条件与定价公式的应用与经济解释.  相似文献
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In this paper, motivated by the concepts of increasing (alternating) non-crossing trees, the problem of consecutive pattern avoidances in non-crossing trees is proposed. Some given patterns of length two and three are investigated in detail. The Lagrange inversion formula is used to obtain the explicit formulas for these cases. Bijections are established between non-crossing trees avoiding special patterns and Schröder paths.  相似文献
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The pebbling number of a graph G, f(G), is the least n such that, no matter how n pebbles are placed on the vertices of G, we can move a pebble to any vertex by a sequence of pebbling moves, each move taking two pebbles off one vertex and placing one on an adjacent vertex. Let p1,p2,…,pn be positive integers and G be such a graph, V(G)=n. The thorn graph of the graph G, with parameters p1,p2,…,pn, is obtained by attaching pi new vertices of degree 1 to the vertex ui of the graph G, i=1,2,…,n. Graham conjectured that for any connected graphs G and H, f(G×H)≤f(G)f(H). We show that Graham’s conjecture holds true for a thorn graph of the complete graph with every by a graph with the two-pebbling property. As a corollary, Graham’s conjecture holds when G and H are the thorn graphs of the complete graphs with every .  相似文献
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本文探讨沿如下新的思路构造投资组合来最有效地单向"跟踪"某个金融指数;为灵活刻画不同投资者对跟踪风险的感知,我们采用跟踪偏差相应阶数的下半矩作为风险的度量;为较好描述证券收益分布的厚尾现象,我们假设市场上风险资产的收益服从多元t分布.在分析基于上述框架所建立跟踪优化模型基本性质的同时,我们还设计出相应的求解算法.实证检验结果不仅表明新模型与算法的有效性和实用价值,而且较好地克服了基于MAD等准则的传统跟踪方法的不足.  相似文献
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