Runtime and memory consumption analyses for machine learning R programs

R is a multi-paradigm language with a dynamic type system, different object systems and functional characteristics. These characteristics support the development of statistical algorithms at a high level of abstraction. Although R is commonly used in the statistics domain a big disadvantage are its runtime problems when handling computation-intensive algorithms. Especially in the domain of machine learning the execution of pure R programs is often unacceptably slow. Our long-term goal is to resolve these issues and in this contribution we used the traceR tool to analyse the bottlenecks arising in this domain. Here we measured the runtime and overall memory consumption on a well-defined set of classical machine learning applications and gained detailed insights into the performance issues of these programs.     

企业裁员优化模型的建立及遗传算法的运用

通过调研建立一个比较全面的裁员标准体系,用来计算企业中每个员工对企业的贡献价值,再把这个过程抽象为一个带约束条件的最优化的数学模型,用遗传算法对其求解,进而确定裁减的人员。这样就解决了企业在裁减人员过程中主观地决定裁减人数的问题。该模型能够给管理者提供一个使企业整体利益最大化的精确裁减人数以及被裁的人员清单,提高了决策的科学性,也为管理人员使用计算机提高决策的正确性和高效性提供了参考。     

Deletions in random binary search trees: A story of errors

The usual assumptions for the average case analysis of binary search trees (BSTs) are random insertions and random deletions. If a BST is built by n random insertions the expected number of key comparisons necessary to access a node is 2 ln n+O(1). This well-known result is already contained in the first papers on such ‘random’ BSTs. However, if random insertions are intermixed with random deletions the analysis of the resulting BST seems to become more intricate. At least this is the impression one gets from the related publications since 1962, and it is quite appropriate to speak of a story of errors in this context, as will be seen in the present survey paper, giving an overview on this story.     

启发式教学的应用

对立于注入式教学的启发式教学是尊重学生的人格、主体性,发挥学生的学习主动性、积极性、创造性的民主的教学方法;它体现了人本主义的教学理念,具有辩证唯物主义的哲学品格;提问启发式、反诘启发式、追问启发式、对比启发式、讨论、辩论式是启发式教学的常用教学方法。     

高等学校开设研究型课程的新思维

高等学校培养的人才要适应未来需要,就必须建立和开设研究型课程,建立和开设研究型课程的最基本的要求就是能给学生提供技术创新的人文基础,创新的价值观念和未来创新所需要的科学技术哲学思想,探索和启发学生的发现式思维,使其在未来的工作中能够进行开拓、探索和创新。西安交大工业设计系在开设研究型课程中进行了积极的探索,跳出"跟随外国先进水平"的思维方式,建立自己独特的设计思维体系的研究型课,现在开设的主要课程有《工业社会学》、《工业设计心理学》、《人机界面设计》、《设计美学》等。     

On Approximate Graph Colouring and MAX-k-CUT Algorithms Based on the θ-Function

The problem of colouring a k-colourable graph is well-known to be NP-complete, for k 3. The MAX-k-CUT approach to approximate k-colouring is to assign k colours to all of the vertices in polynomial time such that the fraction of `defect edges' (with endpoints of the same colour) is provably small. The best known approximation was obtained by Frieze and Jerrum (1997), using a semidefinite programming (SDP) relaxation which is related to the Lovász -function. In a related work, Karger et al. (1998) devised approximation algorithms for colouring k-colourable graphs exactly in polynomial time with as few colours as possible. They also used an SDP relaxation related to the -function.In this paper we further explore semidefinite programming relaxations where graph colouring is viewed as a satisfiability problem, as considered in De Klerk et al. (2000). We first show that the approximation to the chromatic number suggested in De Klerk et al. (2000) is bounded from above by the Lovász -function. The underlying semidefinite programming relaxation in De Klerk et al. (2000) involves a lifting of the approximation space, which in turn suggests a provably good MAX-k-CUT algorithm. We show that of our algorithm is closely related to that of Frieze and Jerrum; thus we can sharpen their approximation guarantees for MAX-k-CUT for small fixed values of k. For example, if k = 3 we can improve their bound from 0.832718 to 0.836008, and for k = 4 from 0.850301 to 0.857487. We also give a new asymptotic analysis of the Frieze-Jerrum rounding scheme, that provides a unifying proof of the main results of both Frieze and Jerrum (1997) and Karger et al. (1998) for k 0.     

A Novel Evolutionary Formulation of the Maximum Independent Set Problem

We introduce a novel evolutionary formulation of the problem of finding a maximum independent set of a graph. The new formulation is based on the relationship that exists between a graphs independence number and its acyclic orientations. It views such orientations as individuals and evolves them with the aid of evolutionary operators that are very heavily based on the structure of the graph and its acyclic orientations. The resulting heuristic has been tested on some of the Second DIMACS Implementation Challenge benchmark graphs, and has been found to be competitive when compared to several of the other heuristics that have also been tested on those graphs.     

“行/列约束法”在外贸进出口货柜运输业务上的应用

外贸日常进出口业务活动中,我们经常遇到如何利用物质资源条件,求取并实现最理想目标的问题。本文研究了货柜运输业务上三维装箱问题,给出了一个基于管理数学中“行约法 /列约法”的摆放方法。通过和外贸进出口业务常规计算方法比较,降低了创汇成本,增加了经济效益。同时和其它方法比较发展,我们的方法在实际货柜装箱操作上,方便实用。     

Approximation algorithms and hardness results for labeled connectivity problems

Let G=(V,E) be a connected multigraph, whose edges are associated with labels specified by an integer-valued function ℒ:E→ℕ. In addition, each label ℓ∈ℕ has a non-negative cost c(ℓ). The minimum label spanning tree problem (MinLST) asks to find a spanning tree in G that minimizes the overall cost of the labels used by its edges. Equivalently, we aim at finding a minimum cost subset of labels I⊆ℕ such that the edge set {e∈E:ℒ(e)∈I} forms a connected subgraph spanning all vertices. Similarly, in the minimum label s – t path problem (MinLP) the goal is to identify an s–t path minimizing the combined cost of its labels. The main contributions of this paper are improved approximation algorithms and hardness results for MinLST and MinLP.     

基于遗传算法的具有主次仓库的企业资源供应链管理模型研究

本文研究如何在有容量限制的主次仓库间分配客户需求的企业资源供应链管理问题,当主仓库不能满足客户需求时,通过一个次仓库弥补主仓库的不足。首先把该问题构造成一个整数规划模型,其次,运用遗传算法加以解决,实际应用和数值分析说明了该遗传算法在解决这类问题中的有效性和实用生。