一类具有T^k工件排序问题的计算复杂性

排序问题近年来已得到广泛的注意,并已获得许多深刻的结果。在古典排序中,一个最普通的约定是:每个时刻每个工件至多在一台机器上加工。由于微型计算机的飞速发展,要求我们打破上面的假设条件,也就是允许某些工件在多台机器上同时进行加工。文献[1]和[2]已得到preemptive排序问题的部分结果,本文讨论一类简单的     

关于排序模型1｜·｜ri≥0｜ ∑n i=1 to n vi的注记

设J={J1,…,Jn}是n个工件的集合,M是一台机器.每个工件Ji要在机器M上加工一次,而且是相继只加工一次,即加工不能够中断.Ji的加工时间是pi,准备时间是ri,即Ji不能在ri之前加工,要求完工的期限是di,即工件Ji的加工应该在di之前完成.否则,这个工件将被拒绝放在一旁.我们的目的是寻找排序算法A,当使用到给定的J上时,使被拒绝的工件个数为最少. 1978年Kise，Ibaraki，Mine等在条件ri〈rj蕴涵di≤dj（对于任何1≤i，j≤n）下，对于任何给定的J找到算法A他们在论文[1]中“证明”算法A是最优算法．最近，李杉林给出一个例子说明他们的证明中的一个关键引理是错误的．本文作者在书[2]中也沿用了这个错误的“证明”．对于算法A的最优性，本文给出一个新的简单的证明．     

费用有限的柔性两机自由作业与流水作业排序问题

研究制造商加工环境为两机自由作业和流水作业柔性排序问题,即工件既可以在制造商两台机器上加工,又可以转包给承包商机器加工.承包商有足够多机器,使得每台机器至多加工一个工件.工件在制造商及承包商机器上所需加工时间及费用均不同.本文需要确定被转包的工件集及未转包工件的加工顺序,在加工及转包总费用不超过给定值的情况下,分别极小...     

带约束的平行机排序的一个近似算法

讨论有资源约束和有机器准备时间的平行机排序问题,资源约束为每个机器至多可加工k个工件,在极小化makespan的上给出了一个匹配算法,证明其最坏情况最紧界是2-m^-1,并进一步给出了它的两个带参数的最坏情况界。     

一类带机器准备时间的排序复杂性及算法

1引言文[2-4]中考虑了如下定义的一个排序模型：m台同型机器加工n个工件，每个工件在零时刻到达，第i个工件需加工时间pi,而各机器有各自的准备时间Tj≥0,怎样安排工件加工顺序，使机器总完工时间（makespan）尽可能早．这是一个强NP-完全问题．本文考虑增加这样一个约束，即每     

排序的贪婪算法的参数上界

本文研究平行机排序中最著名的贪婪算法─LPT算法的性质．经典排序中机器随时可以开始加工．本文研究机器不都是从开始就可以加工,而是需要一个准备时间,也就是说本文研究各台机器最早可以开工的时间可以不同的同型号平行机（ideaticalParallel）的排序问题,分析LPT算法得到的近似解的参数上界．     

带两个服务等级的三台机最优在线算法

研究了带服务等级约束的三台平行机在线排序问题.每台机器和每个工件的服务等级为1或者2,工件只能在等级不高于它的机器上加工,即等级为1的工件只能在等级为1的机器上加工,等级为2的工件可在所有机器上加工.每个工件的加工时间为一个单位,目标是极小化所有工件的总完工时间.考虑两种情形:当一台机器等级为1,两台机器等级为2时,给出了竞争比为17/14的最优在线算法;当两台机器等级为1,一台机器等级为2时,给出了竞争比为43/36的最优在线算法.     

机器具有学习效应的供应链排序问题

研究了机器具有学习效应的供应链排序问题.有多个客户分布在不同位置,每个客户都有一定数量的工件需要在一台机器上进行加工.每个客户的工件在机器上加工时具有学习效应,即后面加工的工件实际加工时间是逐渐缩短的.工件生产完后需要运输到相应的客户处,每一批配送需要花费一定的时间和费用.这里研究了供应链排序理论中主要的四个目标函数,分析了这些问题的复杂性,对于一些情况给出了它们的最优算法.     

工件延误和可拒绝下的单机重新排序问题的近似方案

研究工件延误产生干扰且延误工件可拒绝下的单机重新排序问题.在该问题中,给定计划在零时刻到达的一个工件集需在一台机器上加工,工件集中的每个工件有它的加工时间和权重,在工件正式开始加工前,按照最短赋权加工时间优先的初始排序已经给定,目标函数是极小化赋权完工时间和,据此每个工件的承诺交付截止时间也给定.然而,在工件正式开始加...     

一个多项式时间可解的自由作业排序问题

一个多项式时间可解的自由作业排序问题俞国胜（上海大学理学院数学系，上海２０１８００）１引言和记号自由作业（ｏＰｅｒｌｓｈｏＰ）排序问题是：有ｎ个工件Ｊ一《ＪＩ，人，··，人｝和。台机器Ｍ一｛ＭＩ，ＭＺ，…；Ｍｔｎ｝，每个工件Ｊｊ需要在机器Ｍｉ上加工，...     

Scheduling multiprocessor tasks on a dynamic configuration of dedicated processors

In the classical scheduling theory, it is widely assumed that a task can be processed by only one processor at a time. With the rapid development of technology, this assumption is no longer valid. In this work we present a problem of scheduling tasks, each of which requires for its processing a set of processors simultaneously and which can be executed on several alternative sets of processors. Scheduling algorithms based on dynamic and linear programming are presented that construct minimum length non-preemptive and preemptive schedules, respectively. Results of computational experiments are also reported.This research was partially supported by a KBN grant and by project CRIT.     

Scheduling multiprocessor tasks with chain constraints

This paper is concerned with a new model in deterministic scheduling theory, where certain tasks may require more than one processor at a time. This model is motivated by several applications of multimicroprocessor systems and it has received much attention in the last years. In the paper it is assumed that each task can be processed on any processor subset of a given task-dependent size. Tasks are nonpreemptable and there are precedence constraints among them. It is proved that the problem of minimizing schedule length is NP-hard for three processors even if all the tasks have unit processing times and precedence constraints form a set of chains. Thus, it is unlikely to be solvable in polynomial time. On the other hand, two low order polynomial-time algorithms are given for the m processor case if processor requirements of the tasks in each chain are either uniform or monotonically decreasing (increasing).     

Scheduling Malleable Tasks on Parallel Processors to Minimize the Makespan

The problem of optimal scheduling n tasks in a parallel processor system is studied. The tasks are malleable, i.e., a task may be executed by several processors simultaneously and the processing speed of a task is a nonlinear function of the number of processors allocated to it. The total number of processors is m and it is an upper bound on the number of processors that can be used by all the tasks simultaneously. It is assumed that the number of processors is sufficient to process all the tasks simultaneously, i.e. n≤m. The objective is to find a task schedule and a processor allocation such that the overall task completion time, i.e. the makespan, is minimized. The problem is motivated by real-life applications of parallel computer systems in scientific computing of highly parallelizable tasks. An O(n) algorithm is presented to solve this problem when all the processing speed functions are convex. If these functions are all concave and the number of tasks is a constant, the problem can be solved in polynomial time. A relaxed problem, in which the number of processors allocated to each task is not required to be integer, can be solved in O(nmax {m,nlog ² m}) time. It is proved that the minimum makespan values for the original and relaxed problems coincide. For n=2 or n=3, an optimal solution for the relaxed problem can be converted into an optimal solution for the original problem in a constant time.     

A variable neighbourhood search algorithm for the constrained task allocation problem

A variable neighbourhood search algorithm that employs new neighbourhoods is proposed for solving a task allocation problem whose main characteristics are: (i) each task requires a certain amount of resources and each processor has a capacity constraint which limits the total resource of the tasks that are assigned to it; (ii) the cost of solution includes fixed costs when using processors, task assignment costs, and communication costs between tasks assigned to different processors. A computational study shows that the algorithm performs well in terms of time and solution quality relative to other local search procedures that have been proposed.     

The master-slave paradigm in parallel computer and industrial settings

The master-slave paradigm finds important applications in parallel computer scheduling, semiconductor testing, machine scheduling, transportation, maintenance management and other industrial settings. In the master-slave model considered in this paper a set of jobs is to be processed by a system of processors. Each job consists of a preprocessing task, a slave task and a postprocessing task that must be executed in this order. The pre- and post-processing tasks are to be processed by a master processor while the slave task is processed by a slave processor. In this paper, we motivate the master-slave model and develop bounded performance approximation algorithms for the unconstrained makespan minimization problem as well as for multiple master systems.This work was supported in part by the National Science Foundation under grant MIP-9103379 and the Army Research Office under grant DAA H04-95-1-0111.     

Minimizing the total weighted late work in scheduling of identical parallel processors with communication delays

This paper addresses a certain type of scheduling problem that arises when a parallel computation is to be executed on a set of identical parallel processors. It is assumed that if two precedence-related tasks are processed on two different processors, due to the information transferring, there will be a task-dependent communication delay between them. For each task, a processing time, a due date and a weight is given while the goal is to minimize the total weighted late work. An integer linear mathematical programming model and a branch-and-bound algorithm have been developed for the proposed problem. Comparing the results obtained by the proposed branch-and-bound algorithm with those obtained by CPLEX, indicates the effectiveness of the method.     

Scheduling UET task systems with concurrency on two parallel identical processors

Problems with unit execution time tasks and two identical parallel processors have received a great deal of attention in scheduling theory. In contrast to the conventional models, where each task requires only one processor, we consider a situation when a task may require both processors simultaneously. For problems without precedence constraints we present several polynomial time algorithms which complement recent results of Lee and Cai. We also show that the introduction of precedence constraints leads to NP-hardness results for maximum lateness and mean flow time objective functions. For the maximum lateness problem, a family of algorithms, based upon the idea of modified due dates, is considered. The worst case behaviour of these algorithms is analysed, and it is shown that the same upper bound is tight for each algorithm of this family.     

Stochastic Approximation in Real Time: A Pipe Line Approach

1.IntroductionTheobjectiveofthisworkistostudystochasticapproximationinrea1time.Apipelineapproachissuggested.Asymptoticpropertiesoftheprocedurearedeve1oped,andcomparisonsofrateofconvergencewiththeclassicalalgorithmsaremade.LetxeE',andf(.):EL-FL-Thetraditio…     

Graph models for scheduling systems with machine saturation property

Let be a set of n independent tasks and a set of m processors. During each time instant, each processor can be used by a single task at most. A schedule is for each task an allocation of one or more time intervals to one or more processors. A schedule is said to be optimal if it minimizes the maximum completion time. We say a schedule S has the machine saturation property (MS property) if, at any time instant of task execution, all the machines are simultaneously busy. In this paper, we analyze the conditions under which a parallel scheduling system allows a schedule with the MS property. While for some simple models the analytical conditions can be easily stated, a graph model approach is required when conflicts of processor usage are present. For this reason, we define the class of saturated graphs that correspond to scheduling systems with the MS property. We present efficient graph recognition algorithms to verify the MS property directly on some classes of saturated graphs     

First fit decreasing scheduling on uniform multiprocessors

Independent tasks are nonpreemptively scheduled on m≥2 processors which are assumed to have different speeds. The purpose of this paper is to show that the worst case ratio of the multifit algorithm MF, which is based on the bin-packing method FFD (first fit decreasing), depends on the order of the processors and that the MF has a better worst case behavior than the well-known LPT algorithm for certain processor configurations.