Infeasible-interior-point algorithm for a class of nonmonotone complementarity problems and its computational complexity

This paper presents an infeasible-interior-point algorithm for a class of nonmonotone complementarity problems, and analyses its convergence and computational complexity. The results indicate that the proposed algorithm is a polynomial-time one.     

Risk models for the Prize Collecting Steiner Tree problems with interval data

Given a connected graph G=(V,E)with a nonnegative cost on each edge in E,a nonnegative prize at each vertex in V,and a target set V′V,the Prize Collecting Steiner Tree(PCST)problem is to find a tree T in G interconnecting all vertices of V′such that the total cost on edges in T minus the total prize at vertices in T is minimized.The PCST problem appears frequently in practice of operations research.While the problem is NP-hard in general,it is polynomial-time solvable when graphs G are restricted to series-parallel graphs.In this paper,we study the PCST problem with interval costs and prizes,where edge e could be included in T by paying cost xe∈[c e,c+e]while taking risk(c+e xe)/(c+e c e)of malfunction at e,and vertex v could be asked for giving a prize yv∈[p v,p+v]for its inclusion in T while taking risk(yv p v)/(p+v p v)of refusal by v.We establish two risk models for the PCST problem with interval data.Under given budget upper bound on constructing tree T,one model aims at minimizing the maximum risk over edges and vertices in T and the other aims at minimizing the sum of risks over edges and vertices in T.We propose strongly polynomial-time algorithms solving these problems on series-parallel graphs to optimality.Our study shows that the risk models proposed have advantages over the existing robust optimization model,which often yields NP-hard problems even if the original optimization problems are polynomial-time solvable.     

一类新的求解P_*(κ)阵线性互补问题的多项式内点算法

利用核函数及其性质,对P_*(k)阵线性互补问题提出了一种新的宽邻域不可行内点算法.对核函数作了一些适当的改进,所以是不同于Peng等人介绍的自正则障碍函数.最后证明了算法具有近似O((1+2k)n3/4log(nμ~0)/ε)多项式复杂性,是优于传统的基于对数障碍函数求解宽邻域内点算法的复杂性.     

Complexity of linear programming

The complexity of linear programming is discussed in the “integer” and “real number” models of computation. Even though the integer model is widely used in theoretical computer science, the real number model is more useful for estimating an algorithm's running time in actual computation.Although the ellipsoid algorithm is a polynomial-time algorithm in the integer model, we prove that it has unbounded complexity in the real number model. We conjecture that there exists no polynomial-time algorithm for the linear inequalities problem in the real number model. We also conjecture that linear inequalities are strictly harder than linear equalities in all “reasonable” models of computation.     

On the complexity of approximating a KKT point of quadratic programming

We present a potential reduction algorithm to approximate a Karush—Kuhn—Tucker (KKT) point of general quadratic programming (QP). We show that the algorithm is a fully polynomial-time approximation scheme, and its running-time dependency on accuracy (0, 1) is O((l/) log(l/) log(log(l/))), compared to the previously best-known result O((l/)²). Furthermore, the limit of the KKT point satisfies the second-order necessary optimality condition of being a local minimizer. © 1998 The Mathematical Programming Society, Inc. Published by Elsevier Science B.V.Research support in part by NSF grants DDM-9207347 and DMI-9522507, and the Iowa Business School Summer Grant.     

网络最小覆盖流问题

网络流理论中最基本的模型是最大流及最小费用流问题. 为研 究堵塞现象, 文献中出现了最小饱和流问题, 但它是NP-难的. 研究类似的最小覆盖流问题, 即求一流, 使每一条弧的流量达到一定的额定量, 而流的值为最小. 主要结果是给出多项式时间算法, 并应用于最小饱和流问题.     

单架飞机受干扰后飞机路径恢复多项式算法研究

飞机路径恢复是航班调整中保证航班能够运行的必要条件之一,而传统目标下的飞机路径优化问题是NP-hard的。本文针对单架飞机受到干扰后,基于最小最大目标的同机型飞机路径最优化问题,给出了一个新的多项式时间算法。首先基于航空公司调整航班的常用原则,提出把最大航班延误时间最小化作为问题的目标。然后根据问题的一些特点和目标形式,设计出解构造算法,得到飞机路径恢复问题的最优解,并分析出算法的复杂度为O(n²)。相对于一般的最小最大二分图匹配算法(复杂度为O(n³log(n))),该算法具有较小的时间复杂度。最后用实例验证了解构造算法的有效性。该研究结果将为航空公司减少航班延误提供理论和方法支持。     

线图上的团染色问题

设G=(V,E)为简单图, G的每个至少有两个顶点的极大完全子图称为G的一个团. 图的团染色定义为给图的点进行染色使得图中没有单一颜色的团, 也就是说每一个团具有至少2种颜色.图的一个k-团染色 是指用k 种颜色给图的点着色使得图G 的每一个团至少有2种颜色.图G的团染色数\chi_{C}(G)是指最小的数k使得图G 存在k-团染色. 首先指出了完全图的线图的团染色数与推广的Ramsey 数之间的一个联系, 其次对于最大度不超过7的线图给出了一个最优团染色的多项式时间算法.     

A Polynomial-Time Algorithm for Finding Regular Simple Paths in Outerplanar Graphs

Let G be a labeled directed graph with arc labels drawn from alphabet Σ, R be a regular expression over Σ, and x and y be a pair of nodes from G. The regular simple path (RSP) problem is to determine whether there is a simple path p in G from x to y, such that the concatenation of arc labels along p satisfies R. Although RSP is known to be NP-hard in general, we show that it is solvable in polynomial time when G is outerplanar. The proof proceeds by presenting an algorithm which gives a polynomial-time reduction of RSP for outerplanar graphs to RSP for directed acyclic graphs, a problem which has been shown to be solvable in polynomial time.     

A .699-approximation algorithm for Max-Bisection

We present a .699-approximation algorithm for Max-Bisection, i.e., partitioning the nodes of a weighted graph into two blocks of equal cardinality so as to maximize the weights of crossing edges. This is an improved result from the .651-approximation algorithm of Frieze and Jerrum and the semidefinite programming relaxation of Goemans and Williamson. Received: October 1999 / Accepted: July 2000?Published online January 17, 2001