Showing papers on "Heuristic published in 1975"

A Comparison of Heuristic and Optimum Solutions in Resource-Constrained Project Scheduling

Abstract: The problem addressed is that of scheduling the activities of a project network to minimize project duration under conditions of multiple limited resource requirements and availabilities. Various heuristic sequencing rules have been applied to this problem, and the effectiveness of these rules relative to one another has been previously compared in the literature. However, there have been no previous comparisons of the effectiveness of these rules relative to an optimum solution. This paper makes such a comparison of eight different heuristic scheduling rules, including those found most effective in previous research on this problem. Results are presented for a total of eighty-three different multi-resource problems.

A Dynamic Programming Solution to Cost-Time Tradeoff for CPM

Abstract: To solve the problem of time-cost tradeoff in project management with available models, a choice must be made between heuristic approaches and algorithms based upon restrictive assumptions about the shape of the cost-time functions of the activities. The algorithm presented in this article involves a dynamic-programming approach to determine the allocation which minimizes the duration of the project (critical path). The main advantage of this model is its ability to determine the optimum allocation among activities with arbitrary cost-time functions. Also, computational shortcuts for functions with special properties can be used to increase the efficiency of the model. Objective functions of networks with special structures decompose into sequences of one-dimensional optimization problems. Although some complex networks have objective functions which cannot be fully decomposed, the dimensions of these functions are considerably less than the number of activities involved. If the activities have nonincreas...

Some Temporal Regularities of Spoken Swedish

Abstract: Acoustic segments of speech are known to exhibit a great deal of durational variation. In the present research we have tried to disentagle some of the variables that determine segment durations in spoken (Stockholm) Swedish and estimate the magnitude of the effect contributed by each variable. A tentative theory of segment durations and fundamental frequency control will be proposed. In view of the complexity of the processes that underly the patterning of segment durations in human speech, at the present stage such a theory must necessarily be of a heuristic character serving primarily to increase the precision with which agreement and disagreement between hypotheses and data can be established and to facilitate the construction of still better frameworks. Nevertheless although not intended as a conclusive summary of established facts and principles the present proposal appears capable of accommodating a large body of observations and is meant to supercede the durational descriptions published previously by our research group (Lindblom & Rapp, 1972; Carlson et al. , 1972).

Heuristic techniques in computer-aided circuit analysis

Abstract: A new kind of circuit analysis program, EL, is presented. Whereas other circuit analysis systems rely on classical, formal, analysis techniques, EL employs heuristic "inspection" methods to solve rather complex dc bias circuits. These techniques also give EL the ability to explain any result in terms of its own qualitative reasoning processes. EL's reasoning is based on the concept of a "local one-step deduction" augmented by various "teleological" principles and by the concept of a "macro-element." Several annotated examples of EL in operation and an explanation of how it works are presented. Also how EL can be extended in several directions, including sinusoidal steady-state analysis is shown. Finally, the possible implications of this work for engineering education and computer-aided design technology are discussed briefly. EL is significant not only as a novel approach to circuit analysis but also as an application of Artificial Intelligence techniques to a new and interesting domain.

One machine sequencing to minimize mean flow time with minimum number tardy

Abstract: The problem of sequencing n jobs on one machine is considered, under the multiple objective of minimizing mean flow time with the minimum number of tardy jobs. A simple procedure is first proposed to schedule for minimum flow time with a specified subset of jobs on time. This is used in conjunction with Moore's Algorithm in a simple heuristic producing good and often optimal schedules. A branch-bound algorithm is presented to produce the optimal schedule efficiently with the help of several theorems which eliminate much branching.

Optimal and Heuristic Decisions in Single-and Multi-Item Inventory Systems

Abstract: A comparison of optimal solutions of single-item inventory systems for the three classical policies tZ, sq, and sZ shows that the optimal order levels in the tZ and sZ policies are usually the same, and so are the optimal reorder points in the sq and sZ policies. The total cost for each of the three policies can be expressed as that of a fundamental model using an appropriate equivalent distribution. The fundamental model can be analyzed with ease. It also provides closed-form results for the normal distribution. Heuristic rules are presented allowing the analysis of inventory systems on the basis of their average demand, standard deviation of demand, probability of no demand, lead-time, carrying cost, replenishing cost, and an availability index. Compared with the optimal decisions and costs for identical inventory systems, in which the probability distribution of demand is known, the heuristic rules give excellent results. The optimal and heuristic decisions are extended to multi-item systems in which t...

Optimal and Heuristic Facility Phase-out Strategies

Abstract: This paper presents an efficient branch and bound algorithm and near optimal heuristic algorithms for solving the problem of withdrawing inventory and/or service facilities for a good or service whose overall demand is declining over time. In particular, this paper models the problem faced by a manager who must consider closing up to M initially open and operating support facilities as demand shifts and declines over a T period planning horizon. The criterion is minimization of total estimated discounted costs. The costs considered are the variable operating cost at each facility, the transportation costs between facilities and demand centers, and the costs to operate and close each facility. Computational results are presented for both the optimum finding and heuristic algorithms.

A heuristic problem solving design system for equipment or furniture layouts

Abstract: The Designer Problem Solver (DPS) demonstrates that the computer can perform simple design tasks. In particular, it designs furniture and equipment layouts. This task was chosen because it is simple, well defined, and characteristic of many design tasks in architecture, engineering, urban planning, and natural resource management. These space planning tasks usually involve manipulating two-dimensional representations of objects to create feasible or optimal solutions for problems involving topological and metric spatial constraints. The paper describes extensive tests performed on the program.DPS is a heuristic problem solver with a planning phase prefixed to it. It uses the planning process to give it a sense of direction, diagnostic procedures to locate difficulties, and remedial actions to recover from difficulties. It uses a convex polygon representation to accurately describe the objects and the layout. This representation allows topological and metric constraints to be tested and the design to be easily updated.DPS has been applied to 50 problems. While it is slow and limited in scope, the ideas behind it are general. It demonstrates the need for selectivity in controlling search and the methods used to achieve it: task-specific information, planning, diagnostic procedures, remedial actions, and selective alternative generators.

Near-Optimal Solutions to a 2-Dimensional Placement Problem

Abstract: We consider the problem of placing records in a 2-dimensional storage array so that expected distance between consecutive references is minimized. A simple placement heuristic which uses only relative frequency of access for different records is shown to be within an additive constant of optimal when distance is measured by the Euclidean metric. For the rectilinear and maximum metrics, we show that there is no such heuristic. For the special case in which all access probabilities are equal, however, heuristics within an additive constant of optimal do exist, and their implementation requires solution of differential equations for which we give numerical solutions.

Coordinating Aggregate and Detailed Scheduling in the One-Machine Job Shop: II—Computation and Structure

Abstract: A previous research report of the authors presented a formal model of the one-machine job-shop scheduling problem with variable labor capacity. This report presents some computational experience with the algorithm proposed previously and a discussion of the structural aspects of the problem. Extensions and refinements of the algorithm are introduced to deal with nonsimultaneous job arrivals and the production smoothing problem. These results provide insight into the structure of the aggregate-detailed cost trade-off problem and suggest a good heuristic decision rule for problems of realistic size and complexity.

Sequencing for Assembly Lines with Integer Task Times

Abstract: Two heuristic assembly line balancing procedures (the precedence matrix, enumeration method of Hoffman [Hoffman, Thomas R 1963 Assembly line balancing with a precedence matrix Management Sci 9 (4, July)] and the biased sampling procedure of Arcus [Arcus, Alpert L 1966 COMSOAL: A computer method for sequencing operations for assembly lines E S Buffa, ed Readings in Production and Operations Management John Wiley, New York]) are compared on the balances obtained and the computation time required to solve ALB problems The use of Hoffman's technique with integer task times and a modified trial cycle time selection generally produces improved balances in less computation time for the problems examined A modification to Hoffman's procedure for smoothing balance delay is also reported

A problem-solving monitor for a deductive reasoning task

Abstract: Much of a scientist's work is involved with making inferences and deductions from data. On analysing some of these tasks in greater detail one observes that the task is made up of a series of sub-tasks and that it is not always possible to determine a unique solution for a particular sub-task. That is, the problem-solution involves a search through a solution-space. Recently, a number of programs have been implemented which are capable of solving problems of this kind, e.g. HEURISTIC DENDRAL and SYNCHEM. In this paper we discuss the design and implementation of systems which monitor the student as he attempts to solve problems involving a search of the solution space. To pursue this broad and general problem it was necessary to choose a particular task to be investigated in some depth. The task chosen was the interpretation of Nuclear Magnetic Resonance spectra—a task encountered in university organic chemistry courses. The paper discusses in some detail the design of this particular problem-solving monitor and includes an annotated student protocol and the corresponding problem-solving graph. The paper concludes with an outline of reactions to this program and a discussion of possible further developments.

Vehicle Routing Problems: Formulations and Heuristic Solution Techniques

Abstract: : An essential element of the newspaper logistics system is the allocation and routing of vehicles for the purpose of delivering newspapers on a daily basis. In this paper, the author presents various vehicle routing problems. Formulations defining the mathematical models are discussed in conjunction with several widely-used heuristic solution techniques. The focus is on providing a unified framework for these very difficult combinatorial programming problems.

A heuristic approach to the hierarchical control of multivariable serially connected dynamical systems

Abstract: A heuristic approach is developed for the control of serially connected dynamical systems with and without time delays between the subsystems. The approach enables near optimal control to be achieved and has particularly modest computational requirements. This is illustrated in a number of examples where the overall optimal and the heuristic strategy are compared by digital simulation. Finally, a method is developed for calculating bounds on the suboptimality of the strategy and a numerical example illustrates the approach.

Technical Note—Multidimensional Sequencing Rule

Abstract: This note derives a simple heuristic sequencing rule for determining a minimum discounted cost development sequence of multiple-purpose projects that simultaneously satisfy a number of increasing demands over a finite planning horizon. An evaluation of the heuristic's performance on the solution of a number of real-world water resources problems indicates that it can be an extremely effective planning aid.

Note—Optimal Heuristic Decisions for the s, S Inventory Policy

Abstract: Heuristic decision rules for the s, S policy in probabilistic inventory systems are proposed. The rules require only the knowledge of the mean and standard deviation of demand, probability of no demand, carrying and replenishing costs, desired availability, and leadtime. Numerical results are given to illustrate the application of the rules.

Analysis of a level algorithm for preemptive scheduling

Abstract: Muntz and Coffman give a level algorithm that constructs optimal preemptive schedules on identical processors when the task system is a tree or when there are only two processors. A variation of their algorithm is adapted for processors of different speeds. The algorithm is shown to be optimal on two processors for arbitrary task systems, but not on three or more processors even for trees. Taking the algorithm as a heuristic on m processors and using the ratio of the lengths of the constructed and optimal schedules as a measure, we show that, on identical processors, its performance is bounded by 2 - 2/m. Moreover 2 - 2/m is a best bound in that there exist task systems for which this ratio is approached arbitrarily closely. On processors of different speeds, we derive an upper bound of its performance in terms of the speeds of the given processor system and show that

The heuristic search and the game of chess a study of quiescence, sacrifices, and plan oriented play

Abstract: This paper describes the results of applying the formal heurisitic search algorithm to the game of chess, and the impact of this work on the theory of heuristic search. It is not that the application of the heuristic search can by itself solve the problems at the heart of the computer chess, but that representing these problems within the formalism of the heuristic search will further their common solution. A separate search heuristic is proposed that does offer a common solution to the problems of quiescence, sacrifices, and plan oriented play.

Matrix strategies in heuristics

Abstract: This paper briefly describes the basis of structural mathematics (N. Bourbaki), the elementary structures of genetic psychology (J. Piaget) and the matrix strategies in heuristics (G. Polya). It demonstrates, by epistemological analysis, that there are very close links between mathematical structures, psychological ‘structures’ and heuristic strategies and illustrates practical work according to heuristic matrix strategies by means of a simple example.

Subgradient Optimization, Matroid Problems and Heuristic Evaluation

Abstract: Many polynomial complete problems can be reduced efficiently to three matroids intersection problems. Subgradient methods are shown to yield very good algorithms for computing tight lower bounds to the solution of these problems. The bounds may be used either to construct heuristically guided (branch-and-bound) methods for solving the problems, or to obtain an upper bound to the difference between exact and approx imate solutions by heuristic methods. The existing experience tend to indicate that such bounds would be quite precise.

A Heuristic-adaptive procedure for segmentation of time patterns

Abstract: This paper treats segmentation of time patterns as a heuristic search problem. Segmentation is formulated in terms of image restoration. An observed pattern, which is the stochastically deformed image of a pure image consisting of a number of regimes, is to be segmented to recover the regimed structure. Standard statistical decision methods are not very useful here because of the computational difficulties involved. The search process described here consists of application of a sequence of heuristic-adaptive operators. Each operator is designed to detect certain flaws in previous segmentations and make modifications accordingly. The search path thus generated ends in a loop from among which the final solution is chosen by an evaluating function. Results of experiments with simulated data are presented and discussed.

A Heuristic Approach to Computer Systems Performance Improvement, I: A Fast Prediction Tool

Abstract: : The complexity of current computer systems strongly inhibits management usage of analytic modeling techniques in seeking 'good' computer system performance. As a result, heuristically-based approaches are in order. Implementation of such an approach requires: (1) a means for determining the performance of a given computer system processing a given collection of jobs in accord with a specified schedule, (2) a means for achieving an improved system from a given system, and (3) a technique for determining when to stop this iterative process. The objective of this paper is to describe an analytically driven approach to computer system performance prediction which can achieve execution speeds of approximately two orders of magnitude faster than real time for production batch installations while providing detailed information on device utilizations and delays. Thus, it provides a basic required capability for the development of heuristic approaches to computer system performance improvement.