共查询到20条相似文献,搜索用时 15 毫秒
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Semigroup Forum - The variety generated by the Brandt semigroup $$B_2$$ can be defined within the variety generated by the semigroup $$A_2$$ by the single identity $$x^2y^2\approx y^2x^2$$ . Edmond... 相似文献
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Christian Borgs Jennifer Chayes Ayalvadi Ganesh Amin Saberi 《Random Structures and Algorithms》2010,37(2):204-222
We give a rigorous analysis of variations of the contact process on a finite graph in which the cure rate is allowed to vary from one vertex to the next, and even to depend on the current state of the system. In particular, we study the epidemic threshold in the models where the cure rate is proportional to the degree of the node or when it is proportional to the number of its infected neighbors. © 2010 Wiley Periodicals, Inc. Random Struct. Alg., 2010 相似文献
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Saralees Nadarajah 《Computational Statistics》2008,23(4):667-668
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This study explores how students learn to create, discuss, and reason with representations to solve problems. A summer school algebra class for seventh and eighth graders provided opportunities for students to create and use representations as problem-solving tools. This case study follows the learning trajectories of three boys. Two of the three boys had been low-achievers in their previous math classes, and one was a high achiever. Analysis of all three boys’ written work reveals how their representations became more sophisticated over time. Their small group interactions while problem-solving also show changes in how they communicated and reasoned with representations. For these boys, representation functioned as a learning practice. Through constructing and reasoning with representations, the boys were able to engage in generalizing and justifying claims, discuss quadratic growth, and collaborate and persist in problem-solving. Negotiating different student-constructed representations of a problem also gave them opportunities to act with agency, as they made choices and judgments about the validity of the different perspectives. These findings have implications for the importance of giving all students access to mathematics through representations, with representational thinking serving as a central disciplinary practice and as a learning practice that supports further mathematics learning. 相似文献
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In dynamic graph algorithms the following provide-or-bound problem has to be solved quickly: Given a set S containing a subset R and a way of generating random elements from S testing for membership in R, either (i) provide an element of R, or (ii) give a (small) upper bound on the size of R that holds with high probability. We give an optimal algorithm for this problem. This algorithm improves the time per operation for various dynamic graph algorithms by a factor of O(log n). For example, it improves the time per update for fully dynamic connectivity from O(log3n) to O(log2n). © 1997 John Wiley & Sons, Inc. Random Struct. Alg., 11 , 369–379 (1997) 相似文献
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Ki Mun Jung Lyn C Thomas Mee Chi So 《The Journal of the Operational Research Society》2015,66(10):1656-1668
Data-based scorecards, such as those used in credit scoring, age with time and need to be rebuilt or readjusted. Unlike the huge literature on modelling the replacement and maintenance of equipment there have been hardly any models that deal with this problem for scorecards. This paper identifies an effective way of describing the predictive ability of the scorecard and from this describes a simple model for how its predictive ability will develop. Using a dynamic programming approach one is then able to find when it is optimal to rebuild and when to readjust a scorecard. Failing to readjust or rebuild a scorecard when they aged was one of the defects in credit scoring identified in the investigations into the sub-prime mortgage crisis. 相似文献
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本文的目的有二个,其一是给出反例说明Anstee的两个定理是欠妥的,其二是订正这二个定理。为方便起见,我们沿用[2]中的有关记号和定义。 设R和S分别为m维和n维非负整数向量,P=(P_(ij))_(m×n)为每列至多有一个1的(0,1)-矩阵。令_p(R,S)是一切以R为行和向量、S为列和向量且覆盖(cover)P的(0,1)-矩阵组成的集合。一个列向量a若是_p(R,S)中某个矩阵的第k列,则称a为_p(R,S)的 相似文献
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《Applied Mathematics Letters》2007,20(7):790-794
This work presents a real options approach to the valuation of multiple investment projects, focusing on the case of option to expand and/or to contract. Proper valuation formulas are obtained by solving Black–Scholes PDE and the impact of strategic interaction among multiple options is studied. 相似文献
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