期刊文献+
共找到5篇文章
< 1 >
每页显示 20 50 100
面向不同数据分布的多维直方图算法COCA-Hist 被引量:4
1
作者 曹巍 王珊 +1 位作者 覃雄派 王秋月 《计算机学报》 EI CSCD 北大核心 2008年第6期1013-1024,共12页
基于代价的RDBMS优化器需要对含有范围查询的合取谓词的结果集基数进行准确的估计,多维直方图对多维数据分布进行模拟,避免在估计结果集基数时采用数据独立性假设,造成估计误差过大,进而导致选择非优化的查询执行计划.在不同的数据分布... 基于代价的RDBMS优化器需要对含有范围查询的合取谓词的结果集基数进行准确的估计,多维直方图对多维数据分布进行模拟,避免在估计结果集基数时采用数据独立性假设,造成估计误差过大,进而导致选择非优化的查询执行计划.在不同的数据分布情况下,传统的多维直方图(如MHist-2)效果有很大不同.数据相关系数和值域密度、值域参数是准确刻画多维数据分布的有效指标,文中提出了根据不同的指标采用不同的动态优化的多维直方图算法COCA-Hist,可以大大改善传统多维直方图在平均情况下的准确性.通过分析传统的多维直方图的最坏情况,COCA-Hist的改进算法可以改进传统的多维直方图在最坏情况下的准确性.实验比较了COCA-Hist和传统的多维直方图MHist-2以及GENHist和STHoles的准确性和时间效率.实验显示无论在平均情况下还是在最坏情况下COCA-Hist的改进算法均优于传统的MHist-2直方图,并且COCA-Hist的准确性和创建时间均比GENHist有极大的改善,在准确性方面COCA-Hist较优于STHoles,而在空间预算有限时STHoles的创建时间比COCA-Hist高两个数量级. 展开更多
关键词 多维直方图 数据相关系数 值域密度 值域参数 属性值平均跨度
下载PDF
面向多维混合型数据分布的混合多维直方图初探 被引量:1
2
作者 曹巍 王珊 《计算机应用》 CSCD 北大核心 2009年第9期2487-2490,2519,共5页
现实世界中,多维数据分布常常不是单一一种类型,而是在不同的数据区域中呈现不同类型的数据分布。提出了一种面向多维混合型数据分布的混合多维直方图COCA*-Hist方法。这种方法在给定的空间预算下,根据数据分布空间不同的区域中的数据... 现实世界中,多维数据分布常常不是单一一种类型,而是在不同的数据区域中呈现不同类型的数据分布。提出了一种面向多维混合型数据分布的混合多维直方图COCA*-Hist方法。这种方法在给定的空间预算下,根据数据分布空间不同的区域中的数据分布类型,可以包含多种不同类型的直方桶,从总体上提高直方图的准确性。由于需要对创建多维直方图的树结构进行二次遍历,以识别不同类型的数据分布区域并进行空间预算的重分配,COCA*-Hist时间效率略低于MHist算法,但对因此获得的准确性的提高和面对不同数据分布类型的通用性来说,是可以接受的。 展开更多
关键词 多维直方图 数据相关性 值域密度 混合型多维数据分布
下载PDF
A Modified Earthquake Model of Self-Organized Criticality on Small World Networks 被引量:1
3
作者 LINMin ZHAOXiao-Wei CHENTian-Lun 《Communications in Theoretical Physics》 SCIE CAS CSCD 2004年第4期557-560,共4页
A modified Olami Feder-Christensen model of self-organized criticality on a square lattice with the properties of small world networks has been studied.We find that our model displays power-law behavior and the expone... A modified Olami Feder-Christensen model of self-organized criticality on a square lattice with the properties of small world networks has been studied.We find that our model displays power-law behavior and the exponent τ of the model depends on φ,the density of long-range connections in our network. 展开更多
关键词 self-organized criticality AVALANCHE small world networks
下载PDF
An Intelligent Early Warning Method of Press-Assembly Quality Based on Outlier Data Detection and Linear Regression
4
作者 XUE Shanliang LI Chen 《Transactions of Nanjing University of Aeronautics and Astronautics》 EI CSCD 2020年第4期597-606,共10页
Focusing on controlling the press-assembly quality of high-precision servo mechanism,an intelligent early warning method based on outlier data detection and linear regression is proposed.Linear regression is used to d... Focusing on controlling the press-assembly quality of high-precision servo mechanism,an intelligent early warning method based on outlier data detection and linear regression is proposed.Linear regression is used to deal with the relationship between assembly quality and press-assembly process,then the mathematical model of displacement-force in press-assembly process is established and a qualified press-assembly force range is defined for assembly quality control.To preprocess the raw dataset of displacement-force in the press-assembly process,an improved local outlier factor based on area density and P weight(LAOPW)is designed to eliminate the outliers which will result in inaccuracy of the mathematical model.A weighted distance based on information entropy is used to measure distance,and the reachable distance is replaced with P weight.Experiments show that the detection efficiency of the algorithm is improved by 5.6 ms compared with the traditional local outlier factor(LOF)algorithm,and the detection accuracy is improved by about 2%compared with the local outlier factor based on area density(LAOF)algorithm.The application of LAOPW algorithm and the linear regression model shows that it can effectively carry out intelligent early warning of press-assembly quality of high precision servo mechanism. 展开更多
关键词 quality early warning outlier data detection linear regression local outlier factor based on area density and P weight(LAOPW) information entropy P weight
下载PDF
Vector Meson Mass in Finite Density and Temperature Lattice QCD
5
作者 王睿 陈莹 +6 位作者 宫明 刘川 刘玉斌 刘朝峰 马建平 孟祥飞 张剑波 《Communications in Theoretical Physics》 SCIE CAS CSCD 2015年第5期559-564,共6页
Vector meson mass values are studied at finite chemical potential and temperature in lattice QCD with lattice size of 24 × 122× 6 using two flavors of staggered quarks. The investigation focuses on the chang... Vector meson mass values are studied at finite chemical potential and temperature in lattice QCD with lattice size of 24 × 122× 6 using two flavors of staggered quarks. The investigation focuses on the change of the vector meson mass in the critical region close to T c with two different types of chemical potentials switched on: the isoscalar chemical potential μS and its isovector counterpart μV. It is found that the vector meson mass increases in the QGP phase with both chemical potentials and decreases with μS in the confinement phase. 展开更多
关键词 lattice QCD numerical simulation vector meson
原文传递
上一页 1 下一页 到第
使用帮助 返回顶部