Showing papers on "Heuristic (computer science) published in 1992"

Time Dependent Vehicle Routing Problems: Formulations, Properties and Heuristic Algorithms

Abstract: The time dependent vehicle routing problem (TDVRP) is defined as follows. A vehicle fleet of fixed capacities serves customers of fixed demands from a central depot. Customers are assigned to vehicles and the vehicles routed so that the total time of the routes is minimized. The travel time between two customers or between a customer and the depot depends on the distance between the points and time of day. Time windows for serving the customers may also be present. The time dependent traveling salesman problem (TDTSP) is a special case of the TDVRP in which only one vehicle of infinite capacity is available. Mixed integer linear programming formulations of the TDVRP and the TDTSP are presented that treat the travel time functions as step functions. The characteristics and properties of the TDVRP preclude modification of most of the algorithms that have been developed for the vehicle routing problem. Several simple heuristic algorithms are given for the TDTSP and TDVRP without time windows based on the nea...

HYPER-LP: a system for power minimization using architectural transformations

Abstract: The increasing demand for “portable” computing and communication, has elevated power consumption to be the most critical design parameter. An automated high-level synthesis system, HYPER-LP, is presented for minimizing power consumption in application specific datapath intensive CMOS circuits using a variety of architectural and computational transformations. The sources of power consumption are reviewed and the effects of architectural transformations on the various power components are presented. The synthesis environment consists of high-level estimation of power consumption, a library of transformation primitives (local and global), and heuristic/probabilistic optimization search mechanisms for fast and efficient scanning of the design space. Examples with varying degree of computational complexity and structures are optimized and synthesized using the HYPER-LP system. The results indicate that an order of magnitude reduction in power can be achieved over current-day design methodologies while maintaining the system throughput; in some cases this can be accomplished while preserving or reducing the implementation area.

HYPER-LP: a system for power minimization using architectural transformations

Abstract: An automated high-level synthesis system, HYPER-LP, for minimizing power consumption in application-specific datapath-intensive CMOS circuits using a variety of architectural and computational transformations is presented The sources of power consumption are reviewed, and the effects of architectural transformations on the various power components are presented The synthesis environment consists of high-level estimation of power consumption, a library of transformation primitives (local and global), and heuristic/probabilistic optimization search mechanisms for fast and efficient scanning of the design space Examples with varying degree of computational complexity and structures are optimized and synthesized The results indicate that an order of magnitude reduction in power can be achieved over current-day design methodologies while maintaining the system throughput; in some cases, this can be accomplished while preserving or reducing the implementation area >

End-to-end scheduling to meet deadlines in distributed systems

Abstract: Algorithms for scheduling a class of systems in which all the tasks execute on different processors in turn in the same order are described. This end-to-end scheduling problem is known as the flow-shop problem. Two cases in which the problem is tractable are presented, and a heuristic for the NP-hard general case is evaluated. The traditional flow-shop model is generalized in two directions. First, an algorithm for scheduling flow shops in which tasks can be serviced more than once by some processors is presented. Second, a heuristic algorithm for scheduling flow shops with periodic tasks is described. Scheduling systems with more than one flow shop are considered. >

A more efficient heuristic for solving large p -median problems

Abstract: The Teitz and Bart (1968) vertex substitution heuristic is more robust than competing algorithms and yields solutions with properties that are necessary, but not sufficient, for a global optimum solution. All documented implementations of this algorithm, however, use a naive spatial search procedure, whereas a more informed spatial search procedure, requiring considerably less computation to solve any given problem, is possible. An algorithm incorporating this new search procedure, called the global/regional interchange algorithm, is described. As problem size increases, proportionally larger reductions in processing costs occur.

Information Ratios for Validating Mixture Analyses

Abstract: Determining the number of components in a mixture of distributions is an important but difficult problem. This article introduces a procedure called minimum information ratio estimation and validation (MIREV), which is based on a ratio of Fisher information matrices. The smallest eigenvalue of the information ratio matrix is used to determine the number of components. A measure of uncertainty may be obtained using a bootstrap technique. Simulations illustrate the effectiveness of the procedure. For mixtures of exponential families, an expression for the observed information ratio matrix provides insight to the success of the procedure. Cluster analysis attempts to identify and characterize subpopulations believed to be present in a population. A wide variety of methods, are available, including criterion optimization, hierarchical methods, and various heuristic methods. Criterion optimization techniques, such as mixture analysis, fuzzy clustering, and partitioning methods are popular because they...

System for adapting query optimization effort to expected execution time

Abstract: A system for the automatic adjustment of resources devoted to query optimization according to estimated query execution time. The disclosed system permits the query optimizer to automatically trade off the time spent estimating the execution cost of alternate query execution plans against the potential savings in execution time that one of those alternate plans may yield. The number of alternate plans considered is adjusted by selecting compile-time parameters and heuristic criteria for limiting the primitive database operators used in the alternate plans, thereby establishing a new search space. The parameters and criteria are adjusted according to the estimate of execution cost for the optimal plan from a first search space. The first search space may be relatively small and quickly evaluated. Evaluation of larger subsequent search spaces is optional according to an automatic thresholding process of the disclosed system.

Facets for Polyhedra Arising in the Design of Communication Networks with Low-Connectivity Constraints

Abstract: This paper addresses the important practical problem of designing survivable fiber optic communication networks. This problem can be formulated as a minimum-cost network design problem with certain low-connectivity constraints. Previous work presented structural properties of optimal solutions and heuristic methods for obtaining “near-optimal” network designs. Some facet-inducing inequalities for the convex hull of the solutions to this problem are given. A companion paper describes computational results on real-world telephone network design problems with a cutting plane method based on this work. These computational results are summarized in the last section of this paper.

On the assignment problem of arbitrary process systems to heterogeneous distributed computer systems

Abstract: The authors propose and evaluate an efficient hierarchical clustering and allocation algorithm that drastically reduces the interprocess communications cost while observing lower and upper bounds of utilization for the individual processors. They compare the algorithm with branch-and-bound-type algorithms that can produce allocations with minimal communication cost, and show a very encouraging time complexity/suboptimality tradeoff in favor of the algorithm, at least for a class of process clusters and their random combinations which it is believed occur naturally in distributed applications. The heuristic allocation is well suited for a changing environment, where processors may fail or be added to the system and where the workload patterns may change unpredictably and/or periodically. >

Strategies for Solving Large Location-Allocation Problems by Heuristic Methods

Abstract: Solution techniques for location-allocation problems usually are not a part of microcomputer-based geoprocessing systems because of the large volumes of data to process and store and the complexity of algorithms. In this paper, it is shown that processing costs for the most accurate, heuristic, location-allocation algorithm can be drastically reduced by exploiting the spatial structure of location-allocation problems. The strategies used, preprocessing interpoint distance data as both candidate and demand strings, and use of them to update an allocation table, allow the solution of large problems (3000 nodes) in a microcomputer-based, interactive decisionmaking environment. Moreover, these strategies yield solution times which increase approximately linearly with problem size. Tests on four network problems validate these claims.

The complexity of the Lin-Kernighan heuristic for the traveling salesman problem

Abstract: It is shown that finding a local optimum solution with respect to the Lin–Kernighan heuristic for the traveling salesman problem is PLS-complete, and thus as hard as any local search problem.

A tabu search heuristic for the vehicle routing problem with time windows

Abstract: This paper describes a tabu search heuristic for the Vehicle Routing Problem with Time Windows (VRPTW). The tabu search incorporates an exchange heuristic which is specifically designed for problems with time windows. Computational results on the standard set of problems of Solomon are included at the end of the paper.

Efficient implementation of heuristics for the continuous network design problem

Abstract: In this paper, we present an efficient implementation of heuristic procedures for solving the continuous network design problem where network users behave according to Wardrop's first principle of traffic equilibrium. Numerical results involving a “standard” benchmark problem are given. Also, it is shown that the cost mapping arising in the Iterative-Optimization-Assignment algorithm is integrable if and only if the volume-delay function is of either the BPR or some logarithmic form.

Heuristic algorithms for delivered price spatially competitive network facility location problems

Abstract: We review previous formulations of models for locating a firm's production facilities while simultaneously determining production levels at those facilities so as to maximize the firm's profit. We enhance these formulations by adding explicit variables to represent the firm's shipping activities and discuss the implications of this revised approach. In these formulations, existing firms, as well as new entrants, are assumed to act in accordance with an appropriate model of spatial equilibrium. The firm locating new production facilities is assumed to be a large manufacturer entering an industry composed of a large number of small firms. Our previously reported proof of existence of a solution to the combined location-equilibrium problem is briefly reviewed. A heuristic algorithm based on sensitivity analysis methods which presume the existence of a solution and which locally approximate price changes as linear functions of production perturbations resulting from newly established facilities is presented. We provide several numerical tests to illustrate the contrasting locational solutions which this paper's revised delivered price formulation generates relative to those of previous formulations. An exact, although computationally burdensome, method is also presented and employed to check the reliability of the heuristic algorithm.

Routing in a network with unreliable components

Abstract: A new approach to the joint selection of primary and secondary routes in a network with unreliable components is presented. The mathematical model captures the changes in the operational characteristics of the network as it adapts to failures. Lagrangian relaxation and subgradient optimization techniques are used to obtain good heuristic solutions to the problem, as well as lower bounds to be used as benchmarks against which the quality of the solution is assessed. Results of numerical experiments are reported, and directions for further enhancements of the model are discussed. >

Code assignment for hidden terminal interference avoidance in multihop packet radio networks

Abstract: Hidden terminal interference is caused by the simultaneous transmission of two stations that cannot hear each other, but are both received by the same destination station. The authors investigate the problem of assigning orthogonal codes to stations to eliminate the hidden terminal interference and minimize the number of codes used. It is shown that this problem is computationally intractable, even for very restricted but very realistic network topologies. Optimal algorithms for code assignment in special networks, as well as both centralized and distributed suboptimal heuristic algorithms for general topologies, are presented. The results of extensive simulations to derive the average performance of the proposed heuristics on realistic network topologies are presented. >

Mapping unstructured grid computations to massively parallel computers

Abstract: This thesis investigates the mapping problem: assign the tasks of a parallel program to the processors of a parallel computer such that the execution time is minimized. First, a taxonomy of objective functions and heuristics used to solve the mapping problem is presented. Next, we develop a highly parallel heuristic mapping algorithm, called Cyclic Pairwise Exchange (CPE), and discuss its place in the taxonomy. CPE uses local pairwise exchanges of processor assignments to iteratively improve an initial mapping. A variety of initial mapping schemes are tested and recursive spectral bipartitioning (RSB) followed by CPE is shown to result in the best mappings. For the test cases studied here, problems arising in computational fluid dynamics and structural mechanics on unstructured triangular and tetrahedral meshes, RSB and CPE outperform methods based on simulated annealing. Much less time is required to do the mapping and the results obtained are better. Compared with random and naive mappings, RSB and CPE reduce the communication time twofold for the test problems used. Finally, we use CPE in two applications on a CM-2. The first application is a data parallel mesh-vertex upwind finite volume scheme for solving the Euler equations on 2-D triangular unstructured meshes. CPE is used to map grid points to processors. The performance of this code is compared with a similar code on a Cray-YMP and an Intel iPSC/860. The second application is parallel sparse matrix-vector multiplication used in the iterative solution of large sparse linear systems of equations. We map rows of the matrix to processors and use an inner-product based matrix-vector multiplication. We demonstrate that this method is an order of magnitude faster than methods based on scan operations for our test cases.

Automatic synthesis of 3D asynchronous state machines

Abstract: An automatic synthesis tool (3D) for designing asynchronous controllers from burst-mode specifications, a class of specifications allowing multiple input change fundamental mode operation, is described. An algorithm for constructing a three-dimensional next-state table, a heuristic for encoding states, and a procedure for generating necessary constraints for exact logic minimization are presented. The effectiveness of the 3D implementation and the synthesis procedure on numerous designs including a large realistic example (asynchronous data transfer protocol of the SCSI bus controller) is demonstrated. The latency (input to output delay) and the cycle time (time required for the circuit to stabilize after the excitation) for all benchmark designs using a 0.8- mu m CMOS standard cell library are estimated. >

Behavioral synthesis for easy testability in data path scheduling

Abstract: A data path scheduling algorithm to improve testability without assuming any particular test strategy is presented. A scheduling heuristic for easy testability, based on previous work on data path allocation for testability, is introduced. A mobility path scheduling algorithm to implement this heuristic while also minimizing area is developed. Experimental results on benchmark and example circuits show high fault coverage, short test generation time, and little or no area overhead. >