Tailweight, quantiles and kurtosis: A study of competing distributions

This paper studies analytically and numerically the tail behavior of the symmetric variance-gamma (VG), t, and exponential-power (EP) distributions. Special emphasis is on the VG, which is a direct competitor of the t in the financial context of modeling the distribution of log-price increments.     

Heuristic Procedures for Solving the Discrete Ordered Median Problem

We present two heuristic methods for solving the Discrete Ordered Median Problem (DOMP), for which no such approaches have been developed so far. The DOMP generalizes classical discrete facility location problems, such as the p-median and p-center. The first procedure proposed in this paper is based on a genetic algorithm developed by Moreno Vega (1996) for p-median and p-center problems. Additionally, a second heuristic approach based on the Variable Neighborhood Search metaheuristic (VNS) proposed by Hansen and Mladenović (1997) for the p-median problem is described. An extensive numerical study is presented to show the efficiency of both heuristics and compare them.     

带时间窗偏好的同时配集货且需求可拆分车辆路径问题

针对带时间窗偏好的同时配集货且需求可拆分车辆路径问题,最小化派遣成本、理货成本、时间窗惩罚成本以及油耗成本之和,建立数学模型。设计混合遗传变邻域搜索算法求解问题,在算法中引入时空距离的理念,首先用最近邻插入法和Logistic映射方程生成初始种群;然后利用变邻域搜索算法的深度搜索能力优化算法;提出自适应搜索策略,平衡种群进化所需的广度和深度;设计拆分准则,为各客户设置不同的拆分服务量;提出确定车辆最优出发时间的时差推移法,减少车辆在客户处的等待时间;最后通过多组算例验证本文模型和算法的有效性。     

离散元数值模拟中查找邻居元关系的改进算法

离散元方法是近年发展起来的有前途的新概念数值模拟方法,然而查找邻居元关系耗费大量机时和内存。本文引入一种改进算法-“区域法”,并对其原理、算法、运行时间和空间进行了分析。和原算法中的“窗口法”的比较结果表明,新算法在运行时间和空间方面均明显优于原算法。     

基于模拟退火算法的曲面最短路径求解

通过对路径的节点序列内在关联性的分析,提出了适合曲面最短路径问题的邻域结构,使整段路径的优化问题能够通过局部调整得以实现．将模拟退火算法的框架引入路径寻优中,提出了解决曲面最短路径的随机搜索算法．最后给出了数值仿真实例．     

General properties of some families of graphs defined by systems of equations

In this paper we present a simple method for constructing infinite families of graphs defined by a class of systems of equations over commutative rings. We show that the graphs in all such families possess some general properties including regularity and biregularity, existence of special vertex colorings, and existence of covering maps—hence, embedded spectra—between every two members of the same family. Another general property, recently discovered, is that nearly every graph constructed in this manner edge‐decomposes either the complete, or complete bipartite, graph which it spans. In many instances, specializations of these constructions have proved useful in various graph theory problems, but especially in many extremal problems. A short survey of the related results is included. We also show that the edge‐decomposition property allows one to improve existing lower bounds for some multicolor Ramsey numbers. © 2001 John Wiley & Sons, Inc. J Graph Theory 38: 65–86, 2001     

A topological structure on a set of continous functions with various domains

We construct a topological space of continuous functions which generalizes the previously studied space of functions defined on closed intervals. For the new space, metrizability properties are studied. The results can be applied in the topological theory of ordinary differential equations. Translated fromMatematicheskie Zametki, Vol. 66, No. 1, pp. 76–88, July, 1999.     

A Constraint Programming Framework for Local Search Methods

We propose in this paper a novel integration of local search algorithms within a constraint programming framework for combinatorial optimization problems, in an attempt to gain both the efficiency of local search methods and the flexibility of constraint programming while maintaining a clear separation between the constraints of the problem and the actual search procedure. Each neighborhood exploration is performed by branch-and-bound search, whose potential pruning capabilities open the door to more elaborate local moves, which could lead to even better approximate results. Two illustrations of this framework are provided, including computational results for the traveling salesman problem with time windows. These results indicate that it is one order of magnitude faster than the customary constraint programming approach to local search and that it is competitive with a specialized local search algorithm.     

Characterizing and decomposing classes of threshold,split, and bipartite graphs via 1-Sperner hypergraphs

A hypergraph is said to be 1-Sperner if for every two hyperedges the smallest of their two set differences is of size one. We present several applications of $1$-Sperner hypergraphs to graphs. First, we consider several ways of associating hypergraphs to graphs, namely, vertex cover, clique, independent set, dominating set, and closed neighborhood hypergraphs. For each of them, we characterize graphs yielding $1$-Sperner hypergraphs. These results give new characterizations of threshold and domishold graphs. Second, we apply a characterization of $1$-Sperner hypergraphs to derive decomposition theorems for two classes of split graphs, a class of bipartite graphs, and a class of cobipartite graphs. These decomposition theorems, based on certain matrix partitions, lead to new classes of graphs of bounded clique-width and new polynomially solvable cases of three basic domination problems: domination, total domination, and connected domination.     

Deza graphs with parameters (v,k,k−2,a)

A Deza graph with parameters $\left(v,k,b,a\right)$ is a $k$‐regular graph on $v$ vertices in which the number of common neighbors of two distinct vertices takes one of the following values: $b$ or $a$, where $b\ge a$. In the previous papers Deza graphs with $b=k?1$ were characterized. In this paper, we characterize Deza graphs with $b=k?2$.