Showing papers on "Heuristic (computer science) published in 1983"

A heuristic algorithm for the m-machine, n-job flow-shop sequencing problem

Abstract: In a general flow-shop situation, where all the jobs must pass through all the machines in the same order, certain heuristic algorithms propose that the jobs with higher total process time should be given higher priority than the jobs with less total process time. Based on this premise, a simple algorithm is presented in this paper, which produces very good sequences in comparison with existing heuristics. The results of the proposed algorithm have been compared with the results from 15 other algorithms in an independent study by Park [13], who shows that the proposed algorithm performs especially well on large flow-shop problems in both the static and dynamic sequencing environments.

A Maximum Expected Covering Location Model: Formulation, Properties and Heuristic Solution

Abstract: The maximum covering location model has been used extensively in analyzing locations for public service facilities. The model is extended to account for the chance that when a demand arrives at the system it will not be covered since all facilities capable of covering the demand are engaged serving other demands. An integer programming formulation of the new problem is presented. Several properties of the formulation are proven. A heuristic solution algorithm is presented and computational results with the algorithm are discussed. Directions for future study are also discussed.

Routing to Multiple Destinations in Computer Networks

Abstract: Algorithms for effectively routing messages from a source to multiple destination nodes in a store-and-forward computer network are studied. The focus is on minimizing the network cost (NC), which is the sum of weights of the links in the routing path. Several heuristic algorithms are studied for finding the NC minimum path (which is an NP-complete problem). Among them are variations of a minimum spanning tree (MST) heuristic and heuristics for the traveling salesman problem, both of which use global network information. Another set of heuristics examined are based on using only the shortest paths to the destinations. While the MST algorithm has the best worst case performance among all algorithms, a detailed, empirical study of the "average" performance of the algorithms on typical, randomly chosen networks reveals that simpler heuristics are almost as effective. The NC cost measure is also compared to the destination cost (DC), which is the sum of weights of the shortest path distances to all destinations. A scheme of algorithms is given which trades off between NC and DC.

A Fast Algorithm For The Greedy Interchange For Large-Scale Clustering And Median Location Problems

Abstract: A fast algorithm is described for implementing the greedy interchange heuristic for lise in solving large scale clustering and uncapacitated median location problems. Computational experience is reported for these algorithms on a number of large randomly generated networks and on some difficult problem sets, and comparisons with some other implementations are made. An additional heuristic is proposed for solving these set partitioning problems based on an efficient procedure for achieving the interchange.

Techniques for Facilities Layout: Deciding which Pairs of Activities Should be Adjacent

Abstract: This paper surveys work done to date on the problem of laying out the facilities of some system in terms of specifying which activities are to be adjacent. Each pair of facilities has a closeness rating which represents the desirability that they are located adjacently. Ratings are usually proportional to the flow of goods or people between facilities. The aim of the layout analyst is to design a system so that the sum of the ratings of adjacent pairs is maximized as this represents travel saved. This paper formulates the layout problem and reviews exact and heuristic methods of solution. In the literature review special emphasis is placed on the newly-emerging graph-theoretic techniques which appear promising.

A Minimal Technology Routing System for Meals on Wheels

Abstract: A novel routing system based on a new travelling salesman heuristic was successfully implemented to handle the efficient daily routing of a varying number of vehicles to more than 200 delivery points whose locations change daily. The system had to be easily mantained by one person and require no resources for example, no computer. Our system achieved these objectives, cost less than $50, and, moreover, shortened average travel times by 13% compared to previous performance.

A Branch and Bound Algorithm for Assembly Line Balancing Problems with Formulation Irregularities

Abstract: This paper describes a branch and bound algorithm which can solve assembly line balancing probems with nine modifications to the originally formulated problem of minimizing the required number of assembly stations, given a cycle time, a set of tasks with given deterministic performance times, and between-task precedence relationships. The first two formulation modifications are those of permitting planned imbalance in the total of task performance times at each assembly station, and allowing specific tasks to be assigned to specific types of assembly stations. Seven further problem modifications can be solved by the proposed algorithm, or by any algorithm or heuristic that can solve problems containing these first two modifications. They are: treatment of stochastic task performance times on unpaced lines; requirement of particular tasks to be assigned to particular stations; requirement of task groupings according to task skill levels; requirement of particular tasks to be assigned to only a left-of-line or right-of line station; required task separations; some mixed model situations; and where paralleling of a specified task into two or more stations is permitted. The algorithm is presented in both conceptual and detailed form. Computer computation times to solve a selected cross-sectional sample of problems are provided.

The reconstruction of two-directionally connected binary patterns from their two orthogonal projections

Abstract: A heuristic reconstruction algorithm is described, by which binary matrices can be produced from their two orthogonal projections. It is necessary for proper reconstruction that the binary pattern corresponding to the binary matrix bex- andy-directionally connected. By this method a large class of binary matrices can be reconstructed. It is proved that after a finite number of iterative steps this algorithm produces all thex- andy-directionally connected binary patterns belonging to the given two projections. Finally, some remarks on the implementation of this algorithm and results are presented.

A branch-and-bound-based heuristic for solving the quadratic assignment problem

Abstract: : In this paper a branch and bound algorithm is proposed for solving the quadratic assignment problem. Using symmetric properties of the problem, the algorithm eliminates 'mirror image' branches, thus reducing the search effort. Several routines that transform the procedure into an efficient heuristic are also implemented. These include certain 2-way and 4-way exchanges, selective branching rules, and the use of variable upper bounding techniques for enhancing the speed of fathoming. The computational results are quite encouraging. As an exact scheme, the algorithm solved the 12 facility problem of Nugent et al and the 19 facility problem of Elshafei. More importantly, as a heuristic, the procedure produced the best known solutions for all well-known problems in the literature, and produced improved solutions in several cases. (Author)

File Allocation in a Distributed Computer Communication Network

Abstract: An algorithm is presented to determine locations for the storage of copies of files in store-and-forward computer communications networks. The algorithm determines storage locations which minimize the sum of network file storage costs and message transmission costs. Networks that use adaptive routing techniques are the primary focus. Feasible file locations must satisfy network performance requirements for file availability and delay by message class. An effective method of evaluating delay constraints for networks using adaptive routing techniques is introduced. The algorithm uses the solution to a p-median problem to identify initial candidate file placements. Interaction between a set of file movement rules and a network simulator is employed to modify initial placements to fmd near-optimal locations which satisfy the network performance constraints.

The Isomorphism of Simple File Allocation

Abstract: In this paper, we show that the simple file allocation problem in computer science is isomorphic to the single commodity warehouse location problem in operations research. In simple file allocation, costs due to query and update accesses and storage are considered. Design requirements such as reliability, availability, and delay are not taken into account. Due to this isomorphism, many techniques which have been developed for the warehouse location problem can be applied to solve the simple file allocation problem. Furthermore, there are techniques and conditions developed for one problem which match closely with techniques and conditions developed for the other problem. Based on a combined set of conditions developed in computer science and operations research, a heuristic for file allocation is presented.

Improved Compaction by Minimized Length of Wires

Abstract: The compaction of IC or hybrid layouts by means of the "longest path" method yields a slack in the placement of part of the elements, which, in its turn, can be used to reduce the overall wire-length. The result is an improved electrical performance and a smaller layout. The optimization problem was transformed to a graph-theoretical problem in a way similar to the compaction problem itself. Our procedure starts by adding pieces of information out of the connectivity of the layout to the constraint graph. The succeeding heuristic algorithms generate a new tree of longest paths, taking the linear inequalities and the result of the longest path calculation into consideration. A few examples demonstrate the significant reduction of wire-length and sometimes even an additional reduction of layout area achieved with low computational effort.

Divide and Conquer Heuristics for Minimum Weighted Euclidean Matching

Abstract: We consider the following problem: Given n points in a unit square in the Euclidean plane, find a matching of the points such that the cost (i.e., the sum of the lengths of the edges between matched points) is minimum. In particular, we present a class of linear time heuristic algorithms for this problem and analyze their worst case performance. The worst case performance of an algorithm is defined as the greatest possible cost, as a function of n, of the matching produced by the algorithm on a set of n points. Each of the algorithms studied here divides the unit square into a few smaller regions, and then is applied recursively to the points in each of these regions.

Multicriteria spatial price equilibrium network design: theory and computational results

Abstract: In this paper we consider the problem of determining the optimal design of a transportation network using a vector valued criterion function when the flow pattern is assumed to correspond to a spatial price equilibrium. This problem arises in rail and freight network design, where the spatial price equilibrium is a better behavioral description than the Wardropian user equilibrium characteristic of urban transportation applications. We describe two alternative heuristic solution techniques for the multicriteria spatial price equilibrium network design problem. The first is based on iteration between a pure spatial price equilibrium model and a vector optimization model with only nonnegativity constraints. The second solution technique employs the Hooke and Jeeves algorithm for nonlinear programming to solve a vector optimization model with implicit constraints guaranteeing a spatial price equilibrium flow pattern. In these solution procedures, rather than represent the equilibrium problem as a mathematical program, as is normally done for the Wardropian traffic assignment problems used in urban applications, we employ an original nonlinear complementarity formulation of the spatial price equilibrium problem written entirely in terms of nodal and arc variables and solved extremely efficiently through the iterative application of a linear complementarity algorithm. The nonlinear complementarity formulation allows us to address problems with asymmetric transportation cost, commodity demand and commodity supply functions without the specialized diagonalization/relaxation algorithms required by other approaches.

A two-layer control scheme for merging of automated vehicles

Abstract: This paper extends previous work in the field of automatic vehicle merging and presents a comprehensive solution to the merging control problem. From a control viewpoint automatic merging of two streams of vehicles leads to a complex non-linear, combined continuous/discrete dynamic system of time depending order and structure. The design of a comprehensive merging strategy is carried out through a heuristic approach, based on a detailed analysis of the functional behaviour of the system. Safety requirements together with a consideration of the specifics of the merging process lead to a coupled two-layer control scheme. The theoretical background for the design approach is provided and the performance of the automatic merging control system is discussed based on computer simulations.

Column Generation Based Heuristic Algorithm for Multi-Item Scheduling

Abstract: The column generation algorithm for the multi-item lot-size scheduling problem under resource constraints is examined and improved upon by augmenting simpler heuristic routines in place of the time-consuming Wagner-Whitin dynamic programming routine. The heuristic algorithms thus developed are tested by controlling problem size, setup time, demand variability, and capacity change costs in test problems. The empirical results indicate that the proposed heuristic algorithms reduce CPU time as well as the number of iterations with only a slight loss in optimality.

Stochastic approximation approach to statistical circuit design

Abstract: An application of an algorithm of stochastic approximation (SA) to statistical circuit design (yield optimisation) is proposed Fast initial convergence of the algorithm, typical for all SA methods, has been practically demonstrated The SA methods offer a theoretical background for the statistical circuit design, which has been lacking in mostly heuristic algorithms developed so far

Combinatorial analysis for route first-cluster second vehicle routing

Abstract: Two Route first-cluster second vehicle routing algorithms are contrasted in the first section of the paper. Next, the ‘large’ number of feasible solutions to a multiple travelling salesman problem is established given that each salesman can visit any number of customers in a stated range. An approximate expression is given for the ‘small’ fraction of this solution space searched by a route first-cluster second vehicle routing heuristic. Nevertheless, this heuristic is seen to be a very efficient means of searching its solution space.

The optimality of A* revisited

Abstract: This paper examines the optimality of A*, in the sense of expanding the least number of distinct nodes, over three classes of algorithms which return solutions of comparable costs to that found by A*. We first show that A* is optimal over those algorithms guaranteed to find a solution at least as good as A*'s for every heuristic assignment h. Second, we consider a wider class of algorithms which, like A*, are guaranteed to find an optimal solution. (i.e., admissible) if all cost estimates are optimistic (i.e., h≤h*). On this class we show that A* is not optimal and that no optimal algorithm exists unless h is also consistent, in which case A* is optimal. Finally we show that A* is optimal over the subclass of best-first algorithms which are admissible whenever h≤h*.

Interconnection of Local Computer Networks: Modeling and Optimization Problems

Abstract: We study problems of optimization of the topology of interconnected local computer networks using random access to a single channel. An approach to modeling of the system by a queueing network is proposed: the analytical solution of the model allows us to obtain global performance measures, which may be used as evaluation criteria in network topology optimization problems. A heuristic is proposed for the latter aspect for one class of problems. We also derive from the model the time needed, for a new user which joins the network, to transmit its number of messages.

Optimization of Long Range Major Rehabilitation of Airfield Pavements

Abstract: A procedure has been developed to optimize the planning for major rehabilitative measures for airfield pavements. The procedure is divided into two parts. First, at the project level, an optimum long-range pavement rehabilitative plan is developed for each individual pavement feature (project) of the airfield for each of several levels of funding. The optimum rehabilitative alternative is selected by maximizing the pavement performance as defined by the weighted pavement condition index (PCI) versus time curve. The decision process is modeled by using dynamic programming. The second part of the analysis steps up to the network level of optimization. The criteria for selectin the set of projects is done by maximizing the pavements' performance weighted by the relative value of each project in the network. The rehabilitative projects are selected by using Toyoda's heuristic for 0-1 integer linear programming. The results of the airfield analysis are the selection and timing of major rehabilitative activities. The consequence of many funding levels and any directed work are also determined. Lastly, the pavement engineer can justify an optimum level of funding for long-range planning purposes. The methodology can also be applied directly to highways, roads, and city streets to provide long-range plans for better pavement management.

Reducing Channel Density in Standard Cell Layout

Abstract: The problem of global routing in standard cell layouts so as to minimize total channel density is considered. A sub-problem of this, called the linear net routing problem (LNRP), is defined and is argued to be the key to a successful solution to the general problem. A polynomial-time heuristic for LNRP is presented and its behavior analyzed. In particular, it is proven that the heuristic can produce results as bad as, but no worse than, 50% over the optimal.