jack_dull的博客

非负矩阵分解，可用于文本的话题挖掘.Non-negative matrix factorization (NMF) has previously been shown to be a useful decomposition for multivariate data. Two different multiplicative algorithms for NMF are analyzed. They differ only slightly in the multiplicative factor used in the update rules. One algorithm can be shown to minimize the conventional least squares error while the other minimizes the generalized Kullback-Leibler divergence. The monotonic convergence of both algorithms can be proven using an auxiliary function analogous to that used for proving convergence of the ExpectationMaximization algorithm. The algorithms can also be interpreted as diagonally rescaled gradient descent, where the rescaling factor is optimally chosen to ensure convergence.

本书深入浅出地介绍了lucene——一个开源的使用java语言编写的全文搜索引擎开发包。它通过浅显的语言、大量的图注、丰富的代码示例，以及清晰的结构为读者呈现出作为优秀开源项目的lucene所体现的强大功能。

In logic, a three-valued logic (also trivalent, ternary, trinary logic, or trilean,[citation needed] sometimes abbreviated 3VL) is any of several many-valued logic systems in which there are three truth values indicating true, false and some indeterminate third value. This is contrasted with the more commonly known bivalent logics (such as classical sentential or boolean logic) which provide only for true and false.

Abstract. Query optimizers in object-relational database management systems require users to provide the execution cost models of user-defined functions(UDFs). Despite this need, however, there has been little work done to provide such a model. Furthermore, none of the existing work is self-tuning and, therefore, cannot adapt to changing UDF execution patterns. This paper addresses this problem by introducing a self-tuning cost modeling approach based on the quadtree. The quadtree has the inherent desirable properties to (1) perform fast retrievals, (2) allow for fast incremental updates (without storing individual data points), and (3) store information at different resolutions. We take advantage of these properties of the quadtree and add the following in order to make the quadtree useful for UDF cost modeling: the abilities to (1) adapt to changing UDF execution patterns and (2) use limited memory. To this end, we have developed a novel technique we call the memory-limited quadtree(MLQ). In MLQ, each instance of UDF execution is mapped to a query point in a multi-dimensional space. Then, a prediction is made at the query point, and the actual value at the point is inserted as a new data point. The quadtree is then used to store summary information of the data points at different resolutions based on the distribution of the data points. This information is used to make predictions, guide the insertion of new data points, and guide the compression of the quadtree when the memory limit is reached. We have conducted extensive performance evaluations comparing MLQ with the existing (static) approach.

Tom Lane's illustration on trasation processing in postgreSQL.

数据库领域关于“实视图”方面的论文汇编。是从事数据库研究、应用不可多得的资料。