Time Algorithms (time + algorithms)

Distribution by Scientific Domains


Selected Abstracts


Meeting Real,Time Traffic Flow Forecasting Requirements with Imprecise Computations

COMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 3 2003
Brian L. Smith
This article explores the ability of imprecise computations to address real,time computational requirements in infrastructure control and management systems. The research in this area focuses on the development of nonparametric regression as a means to forecast traffic flow rates for transportation management systems. Nonparametric regression is a forecasting technique based on nearest neighbor searching, in which forecasts are derived from past observations that are similar to current conditions. A key concern regarding nonparametric regression is the significant time required to search for nearest neighbors in large databases. The results presented in this article indicate that approximate nearest neighbors, which are imprecise computations as applied to nonparametric regression, may be used to adequately speed the execution time of nonparametric regression, with acceptable degradations in forecast accuracy. The article concludes with a demonstration of the use of genetic algorithms as a design aid for real,time algorithms employing imprecise computations. [source]


Linear time computation of feasible regions for robust compensators

INTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 9 2001
M. Sami Fadali
Abstract We introduce an application of computational geometry, including figures of merit standard in the analysis of algorithms, to the design of robust control systems. With respect to system transfer function magnitude, we show how to compute feasible regions for compensators whose plant transfer function is the ratio of uncertain interval polynomials. Our solution sweeps the Minkowski quotient set of the corresponding Kharitonov rectangles. Enumerating the winding numbers of Minkowski sum convolution curves, we obtain optimal, linear time algorithms that eliminate three factors from the execution inefficiency of traditional gridding approaches. We illustrate with examples pertinent to quantitative feedback theory (QFT). Copyright 2001 John Wiley & Sons, Ltd. [source]


Refinements on an enumeration scheme for solving a pattern sequencing problem

INTERNATIONAL TRANSACTIONS IN OPERATIONAL RESEARCH, Issue 3 2004
H. H Yanasse
Abstract We introduce some refinements on a branch- and bound-scheme for solving the minimization of open stack problem (MOSP). After representing the MOSP as a graph traversing problem, we attempt to divide the graph into parts aiming to solve the resulting subgraphs independently in order to reduce the search in the branching scheme. Subgraphs with special topologies (such as trees) are solved exactly using polynomial time algorithms. The branching scheme is applied only to the parts that are ,complex'. The refinements introduced produce substantial savings in computational time when the MOSP graph presents some special structures. Limited computational results are presented. [source]


Algorithms for the Weight Constrained Shortest Path Problem

INTERNATIONAL TRANSACTIONS IN OPERATIONAL RESEARCH, Issue 1 2001
Irina Dumitrescu
Given a directed graph whose arcs have an associated cost, and associated weight, the weight constrained shortest path problem (WCSPP) consists of finding a least-cost path between two specified nodes, such that the total weight along the path is less than a specified value. We will consider the case of the WCSPP defined on a graph without cycles. Even in this case, the problem is NP-hard, unless all weights are equal or all costs are equal, however pseudopolynomial time algorithms are known. The WCSPP applies to a number of real-world problems. Traditionally, dynamic programming approaches were most commonly used, but in recent times other methods have been developed, including exact approaches based on Lagrangean relaxation, and fully polynomial approximation schemes. We will review the area and present a new exact algorithm, based on scaling and rounding of weights. [source]


Basic scheduling problems with raw material constraints

NAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 6 2005
Alexander Grigoriev
Abstract One of the achievements of scheduling theory is its contribution to practical applications in industrial settings. In particular, taking finiteness of the available production capacity explicitly into account, has been a major improvement of standard practice. Availability of raw materials, however, which is another important constraint in practice, has been largely disregarded in scheduling theory. This paper considers basic models for scheduling problems in contemporary manufacturing settings where raw material availability is of critical importance. We explore single scheduling machine problems, mostly with unit or all equal processing times, and Lmax and Cmax objectives. We present polynomial time algorithms, complexity and approximation results, and computational experiments. 2005 Wiley Periodicals, Inc. Naval Research Logistics, 2005. [source]


The computational complexity of graph contractions I: Polynomially solvable and NP-complete cases,

NETWORKS: AN INTERNATIONAL JOURNAL, Issue 3 2008
Asaf Levin
Abstract For a fixed pattern graph H, let H -CONTRACTIBILITY denote the problem of deciding whether a given input graph is contractible to H. This paper is part I of our study on the computational complexity of the H -CONTRACTIBILITY problem. We continue a line of research that was started in 1987 by Brouwer and Veldman, and we determine the computational complexity of the H -CONTRACTIBILITY problem for certain classes of pattern graphs. In particular, we pinpoint the complexity for all graphs H with five vertices except for two graphs, whose polynomial time algorithms are presented in part II. Interestingly, in all connected cases that are known to be polynomially solvable, the pattern graph H has a dominating vertex, whereas in all cases that are known to be NP-complete, the pattern graph H does not have a dominating vertex. 2007 Wiley Periodicals, Inc. NETWORKS, 2008 [source]


Approximate L(,1,,2,,,,t)-coloring of trees and interval graphs

NETWORKS: AN INTERNATIONAL JOURNAL, Issue 3 2007
Alan A. Bertossi
Abstract Given a vector (,1,,2,,,,t) of nonincreasing positive integers, and an undirected graph G = (V,E), an L(,1,,2,,,,t)-coloring of G is a function f from the vertex set V to a set of nonnegative integers such that ,f(u) , f(v), , ,i, if d(u,v) = i, 1 , i , t, where d(u,v) is the distance (i.e., the minimum number of edges) between the vertices u and v. An optimal L(,1,,2,,,,t)-coloring for G is one minimizing the largest integer used over all such colorings. Such a coloring problem has relevant applications in channel assignment for interference avoidance in wireless networks. This article presents efficient approximation algorithms for L(,1,,2,,,,t)-coloring of two relevant classes of graphs,trees, and interval graphs. Specifically, based on the notion of strongly simplicial vertices, O(n(t + ,1)) and O(nt2,1) time algorithms are proposed to find ,-approximate colorings on interval graphs and trees, respectively, where n is the number of vertices and , is a constant depending on t and ,1,,,,t. Moreover, an O(n) time algorithm is given for the L(,1,,2)-coloring of unit interval graphs, which provides a 3-approximation. 2007 Wiley Periodicals, Inc. NETWORKS, Vol. 49(3), 204,216 2007 [source]