Showing papers on "Heuristic published in 1991"

When and how to use scenario planning: A heuristic approach with illustration

Abstract: This paper offers a step-by-step analysis of a heuristic approach to scenario planning, taking a managerial perspective. The scenario method is contrasted in general with more traditional planning techniques, which tend to perform less well when faced with high uncertainty and complexity. An actual case involving a manufacturing company is used to illustrate the main steps of the proposed heuristic. Its essence is to identify relevant trends and uncertainties, and blend them into scenarios that are internally consistent. In addition, the scenarios should bound the range of plausible uncertainties and challenge managerial thinking. Links to decision making are examined next, including administrative policies as well as integrative techniques. At the strategic level, a key-success-factor matrix is proposed for integrating scenarios, competitor analysis and strategic vision. At the operational level, Monte Carlo simulation is suggested and illustrated as one useful technique for combining scenario thinking with formal project evaluation (after appropriate translations). The paper concludes with a general discussion of scenario planning, to place it in a broader perspective.

An intelligent dynamic programming for unit commitment application

Abstract: A heuristic improvement of the truncated window dynamic programming has been studied for the unit commitment application. The proposed method employs a variable window size according to load demand increments, and corresponding experimental results indicate a substantial saving in the computation time without sacrificing the quality of the solution. An iterative process for the number of strategies saved in every stage is incorporated to fine tune the optimal solution. >

Distributed constrained heuristic search

Abstract: A model of decentralized problem solving, called distributed constrained heuristic search (DCHS), that provides both structure and focus in individual agent search spaces to optimize decisions in the global space, is presented. The model achieves this by integrating decentralized constraint satisfaction and heuristic search. It is a formalism suitable for describing a large set of distributed artificial intelligence problems. The notion of textures that allow agents to operate in an asynchronous concurrent manner is introduced. The use of textures coupled with distributed asynchronous backjumping, a type of distributed dependency-directed backtracking that the authors have developed, enables agents to instantiate variables in such a way as to substantially reduce backtracking. The approach has been tested experimentally in the domain of decentralized job-shop scheduling. A formulation of distributed job-shop scheduling as a DCHS and experimental results are presented. >

New heuristic algorithms for efficient hierarchical path planning

Abstract: The authors consider one of the most popular approaches to path planning: hierarchical approximate cell decomposition. This approach consists of constructing successive decompositions of the robot's configuration space into rectangloid cells and searching the connectivity graph built at each level of decomposition for a path. Despite its conceptual simplicity, an efficient implementation of this approach raises many delicate questions that have not yet been addressed. The major contributions this work are (1) a novel approach to cell decomposition based on constraint reformulation and (2) a new algorithm for hierarchical search with a mechanism for recording failure conditions. These algorithms have been implemented in a path planner, and experiments with this planner have been carried out on various examples. These experiments show that the proposed planner is significantly (approximately 10 times) faster than previous planners based on the same general approach. >

Dynamic batching heuristic for simultaneous processing

Abstract: This study focuses on computer integrated manufacturing as a means of supporting real-time resource allocation decisions in the semiconductor industry. Two general questions are addressed: (1) how can be global current state of the factory, which would be available in a computer integrated manufacturing system, be summarized into information for decisions? and (2) how much improvement might be expected from such a strategy? Partial answers to these questions for a particular decision, dynamic batch sizing, are provided. It is described how the myopic strategy, minimum batch size rule, performs batch process. A heuristic is proposed to handle batch processing in the look-ahead case, and the sensitivity of this heuristic to forecasting errors is tested. >

Single Machine Tardiness Sequencing Heuristics

Abstract: This paper presents a collection of heuristics for the single machine total (weighted) tardiness problem. The methods considered range from simple quick and dirty heuristics to more sophisticated algorithms exploiting problem structure. These heuristics are compared to interchange and simulated annealing methods on a large set of test problems. For the total tardiness problem a heuristic based on decomposition performs very well, whereas for the total weighted tardiness problem simulated annealing appears to be a viable approach. Our computational results also indicate that straightforward interchange methods perform remarkably well.

Feeder reconfiguration for loss reduction: an application of distribution automation

Abstract: The authors present a comparison of various methods applied to feeder reconfiguration for loss minimization. A new linear programming method using transportation techniques and a new heuristic search method are proposed for comparison with a previously developed heuristic technique which was based on an optimal load flow analysis. The methods are compared on simulations of both a small feeder distribution system, and a larger system based on a model of a public utility commission 44 kV distribution system. This study indicates that linear programming, in the form of transportation algorithms, is not suitable for real-time application to feeder reconfiguration, whereas heuristic approaches, although not optimal, can provide substantial savings if properly formulated and are suitable for real-time implementation. >

Scheduling of Project Networks by Job Assignment

Abstract: A recurring problem in project management involves the allocation of scarce resources to the individual jobs comprising the project. In many situations such as audit scheduling, the resources correspond to individuals skilled labour. This naturally leads to an assignment type project scheduling problem, i.e. a project has to be processed by assigning one of several individuals resources to each job. In this paper we consider the nonpreemptive variant of a resource-constrained project job-assignment problem, where job durations as well as costs depend upon the assigned resource. Regarding precedence relations as well as release dates and deadlines, the question arises, to which jobs resources should be assigned in order to minimize overall costs. For solving this time-resource-cost-tradeoff problem we present a hybrid brand and bound/dynamic programming algorithm with a rather efficient Monte Carlo type heuristic upper bounding technique as well as various relaxation procedures for determining lower bounds. Computational results are presented as well.

Motion planning with six degrees of freedom by multistrategic bidirectional heuristic free-space enumeration

Abstract: A general and efficient method is presented that uses a configuration space for planning a collision-free path among known stationary obstacles for an arbitrarily moving object with six degrees of freedom. The basic approach is to restrict the free space concerning path planning and to avoid executing unnecessary collision detections. The six-dimensional configuration space is equally quantized into cells by placing a regular grid, and the cells concerning path planning are enumerated by simultaneously executing multiple search strategies. Search strategies of different characteristics are defined by assigning different values to the coefficients of heuristic functions. The efficiency of each search strategy is evaluated during free-space enumeration, and a more promising one is automatically selected and preferentially executed. The free-space cells are efficiently enumerated for an arbitrary moving object in all kinds of working environments. The implementation of this method on several examples that have different characteristics is discussed. >

Computing optimal lot sizes in the economic lot scheduling problem

Abstract: This paper treats a version of the Economic Lot Scheduling Problem (ELSP) in which items may be produced several times in different amounts during a cycle. We show how to compute the optimal lot sizes and cycle length, given the sequence of items in a cycle. This requires solving a parametric quadratic program, plus a few EOQ calculations. Our procedure is designed to be used along with a heuristic for selecting the sequence of items in a cycle, such as the one proposed in 1987 by G. Dobson. The two algorithms together comprise a simple, plausible heuristic for the ELSP as a whole.

Distribution system service restoration using a heuristic search approach

Abstract: A heuristic search approach was developed for service restoration of a distribution system. The purpose was to devise a proper restoration plan after the location of a fault has been identified and the faulted zone has been isolated. To reach a restoration plan which satisfies all practical requirements, a set of heuristic rules was compiled through interviews with experienced operators at Taiwan Power Company. A heuristic search algorithm was developed for service restoration following a fault on distribution feeders. The effectiveness of the proposed heuristic service approach was demonstrated by the restoration of the electricity service following a fault in an underground distribution system within the service area of Taipei City District Office of Taiwan Power Company. It was found that the restoration plan can be reached very efficiently. Therefore, it can serve as a valuable tool to help distribution system dispatchers reach a proper restoration plan. >

Parallel Savings Based Heuristics for the Delivery Problem

Abstract: The delivery problem consists of finding a set of routes for a fleet of capacitated vehicles to satisfy the cargo delivery requirements of customers. The vehicles are located in a central depot, and have to fulfill the delivery requirements in a sequence that minimizes total delivery costs. Each vehicle tour starts and terminates at the central depot, and each node is supplied by exactly one vehicle. All vehicles have the same cargo carrying capacity. The paper presents parallel savings algorithms PSAs for generating feasible solutions to this problem. The new algorithms combine the savings approach, with matching based procedures. In computational tests the heuristic produces better solutions than the best known solutions for six problems out of a standard set of 14 difficult test problems. Augmented Lagrangian based lower bounding procedures are developed, and used to evaluate the quality of the solutions generated by PSAs. The lower bounds generated by the augmented Lagrangian are the tightest bounds known for delivery problems. The performance of the PSAs is also compared to tour partitioning based heuristics which have better worst case error bounds. The average quality of solutions generated by PSAs is shown to be significantly superior on large sets of test problems.

A heuristic search approach to feeder switching operations for overload, faults, unbalanced flow and maintenance

Abstract: The general feeder switching problem is essentially combinatorial, i.e. suitable for analysis by heuristic search methods. An explicit search method is developed to identify feasible switching options under the constraint of a radial structure. Feeder overload, transformer overload, phase current over-unbalance, service restoration after faults, and maintenance are considered. The number of switching operations for resolution of these problems is an important factor for practical use. An explicit search structure is proposed. Based on this search structure heuristic rules and evaluation functions are exploited to quickly find a solution with relatively few switching operations and even balancing of system load. The method is efficient and reliable. A distribution system of the Taiwan Power Company is used to test the results. >

A new heuristic solution method in resource‐constrained project scheduling

Abstract: A new heuristic method is presented for the resolution of multiresource constrained conflicts in project scheduling. In attempting to find a minimal makespan solution, the algorithm employs a simple procedure to generate a feasible solution with no backtracking. A postanalysis phase then applies a hill-climbing search. The solution method is different from existing heuristic methods in that it repairs resource conflicts rather than constructs detailed schedules by dispatching activities. Resource-violating sets of activities are identified which must be prevented from concurrent execution because this would violate resource constraints. Repairs are made by imposing an arc to sequence two activities in such a resource violating set. Computational results are compared with those of existing heuristics for the minimal makespan problem.

Determinate literals in inductive logic programming

Abstract: A recent system, FOIL, constructs Horn clause programs from numerous examples. Computational efficiency is achieved by using greedy search guided by an information-based heuristic. Greedy search tends to be myopic but determinate terms, an adaptation of an idea introduced by another new system (GOLEM), has been found to provide many of the benefits of lookahead without substantial increases in computation. This paper sketches key ideas from FOIL and GOLEM and discusses the use of determinate literals in a greedy search context. The efficacy of this approach is illustrated on the task of learning the quicksort procedure and other small but non-trivial list-manipulation functions.

Tour Scheduling and Task Assignment of a Heterogeneous Work Force: A Heuristic Approach

Abstract: The dual problem of work tour scheduling and task assignment involving workers who differ in their times of availability and task qualifications is examined in this paper. The problem is presented in the context of a fast food restaurant, but applies equally well to a diverse set of service operations. Developing a week-long labor schedule is a nontrivial problem, in terms of complexity and importance, which a manager spends as much as a full workday solving. The primary scheduling objective (the manager's concern) is the minimization of overstaffing in the face of significant hourly and daily fluctuations in minimum staffing requirements. The secondary objective (the workers’ concern) is the minimization of the sum of the squared differences between the number of work hours scheduled and the number targeted for each employee. Contributing to scheduling complexity are constraints on the structure of work tours, including minimum and maximum shift lengths and a maximum number of workdays. A goal programming formulation of a representative problem is shown to be too large, for all practical purposes, to be solved optimally. Existing heuristic procedures related to this research possess inherent limitations which render them inadequate for our purposes. Subsequently, we propose and demonstrate a computerized heuristic procedure capable of producing a labor schedule requiring at most minor refinement by a manager.

Improving the equality of workload assignments in assembly lines

Abstract: Most heuristic and optimal methods for assembly line balancing are designed either to minimize the number of workstations required given a production rate, or to maximize the production rate given a fixed number of workstations. This singular focus on line design efficiency typically results in an imbalanced allocation of tasks among the stations. This paper presents a new procedure that rebalances a given solution to level the allocation of tasks. Characteristics of dominant levelled solutions are identified and incorporated into this heuristic procedure. Computational results indicate that the procedure is very effective in levelling workloads.

A heuristic method for FPGA technology mapping based on the edge visibility

Abstract: We present an efficient technology mapping method for lookup table-based FPGA architectures. We first introduce lhc notion of edge visibility. Wc then formulate lhc problem of finding the area-optimal technology mapping as a problem of assigning visibility values to edges of input Boolean network to minimize the number of nodes in the network. We describe an algorithm that assigns visibility valtrcs efficiently. We compare our method to the “xl_cover” algorithm provi(ied by the MIS-pga systcm.

A statistical-heuristic feature selection criterion for decision tree induction

Abstract: The authors present a statistical-heuristic feature selection criterion for constructing multibranching decision trees in noisy real-world domains. Real world problems often have multivalued features. To these problems, multibranching decision trees provide a more efficient and more comprehensible solution that binary decision trees. The authors propose a statistical-heuristic criterion, the symmetrical tau and then discuss its consistency with a Bayesian classifier and its built-in statistical test. The combination of a measure of proportional-reduction-in-error and cost-of-complexity heuristic enables the symmetrical tau to be a powerful criterion with many merits, including robustness to noise, fairness to multivalued features, and ability to handle a Boolean combination of logical features, and middle-cut preference. The tau criterion also provides a natural basis for prepruning and dynamic error estimation. Illustrative examples are also presented. >

Heuristic multi-area unit commitment with economic dispatch

Abstract: An improved multi-area unit commitment and economic dispatch algorithm is proposed. The approach supplements the traditional dynamic programming unit commitment with heuristic adjustments to refine the commitment schedule in each area. A global economic dispatch scheme coordinates the transactions between areas. A new tie-line constraint checking is included which is simple and effective. The overall algorithm can he implemented on an IBM-PC, which can process a fairly large system in a reasonable period of time. Experimental results show the application potential of this method to general multi-area power generation scheduling problems. >

A 3-OPT based simulated annealing algorithm for vehicle routing problems

Abstract: Simulated Annealing is combined with the 3-opt heuristic to solve the vehicle routing problem. The results are encouraging; two examples out of three large size problems gave results as good as the best known 3-opt solution. Preliminary results with the heuristic algorithm are presented.

Heuristic technique for processor and link assignment in multicomputers

Abstract: A graph-based solution to the mapping problem using the simulated annealing optimization heuristic is developed. An automated two-phase mapping strategy is formulated: process annealing assigns parallel processes to processing nodes, and connection annealing schedules traffic connections on network data links so that interprocess communication conflicts are minimized. To evaluate the quality of generated mappings. cost functions suitable for simulated annealing that accurately quantify communications overhead are derived. Communication efficiency is formulated to measure the quality of assignments when the optimal mapping is unknown. The mapping scheme is implemented using the hypercube as a host architecture, and results for several image graphs are presented. >