We sequence storage and retrieval jobs to minimize total travel time of a storage/retrieval (S/R) machine in a two-depot automated storage/retrieval system. These systems include storage systems with aisle-captive S/R...
详细信息
We sequence storage and retrieval jobs to minimize total travel time of a storage/retrieval (S/R) machine in a two-depot automated storage/retrieval system. These systems include storage systems with aisle-captive S/R machines and storage blocks with bridge cranes. The S/R machine must move retrieval unit loads from their current locations in the system to one of the two depots. In addition, it must move storage unit loads from given depots to given locations in the system. We model the problem as an asymmetric traveling salesman problem, which is in general NP-hard. We develop an algorithm to solve the problem in polynomialtime, using the property that the system has two depots and the S/R machine always returns to one of the depots to pick up or deliver a load. Furthermore, we develop additional polynomial time algorithms for the following four special cases: (1) retrieval loads have to be delivered to given depots;(2) the system has one input depot and one output depot;(3) the system has a single depot;and (4) there are arbitrary S/R machine starting and ending locations. The computational results show the effectiveness of the proposed algorithms. Compared to first-come-first-served and nearest neighbor algorithms, commonly used in practice, the total travel time reduces on average by more than 30% and 15%, respectively.
We design a O(n(3)) polynomial time algorithm for finding a (k - 1)- regular subgraph in a k-regular graph without any induced star K(1,3)(claw-free). A polynomial time algorithm for finding a cubic subgraph in a 4-re...
详细信息
We design a O(n(3)) polynomial time algorithm for finding a (k - 1)- regular subgraph in a k-regular graph without any induced star K(1,3)(claw-free). A polynomial time algorithm for finding a cubic subgraph in a 4-regular locally connected graph is also given. A family of k-regular graphs with an induced star K(1,3) (k even, k >= 6), not containing any (k - 1)-regular subgraph is also constructed.
This paper presents two polynomial time algorithms for the constant capacitated lot sizing problem with a batch production. We give several optimality properties for the general problem. Assuming constant production c...
详细信息
This paper presents two polynomial time algorithms for the constant capacitated lot sizing problem with a batch production. We give several optimality properties for the general problem. Assuming constant production capacity, constant batch size and Wagner-Whitin cost structure, we derive O(T-4) and O(T-6) timealgorithms respectively for the case with production capacity being a multiple of the batch size and for the case with an arbitrary fixed capacity. (C) 2012 Elsevier B.V. All rights reserved.
This paper deals with a problem to decide whether a given graph structure appears as a pattern in the structure of a given graph. A graph pattern is a triple p = (V, E, H), where (V, E) is a graph and H is a set of va...
详细信息
This paper deals with a problem to decide whether a given graph structure appears as a pattern in the structure of a given graph. A graph pattern is a triple p = (V, E, H), where (V, E) is a graph and H is a set of variables, which are ordered lists of vertices in V. A variable can be replaced with an arbitrary connected graph by a kind of hyperedge replacements. A substitution is a collection of such replacements. The graph pattern matching problem (GPMP) is the computational problem to decide whether or not a given graph G is obtained from a given graph pattern p by a substitution. In this paper, we show that GPMP for a graph pattern p and a graph G is solvable in polynomialtime if the length of every variable in p is 2, p is of bounded treewidth, and G is connected.
In this paper we consider different classes of nonconvex quadratic problems that can be solved in polynomialtime. We present an algorithm for the problem of minimizing the product of two linear functions over a polyh...
详细信息
We study the multiobjective control of time-discrete systems with given starting and final states. The dynamics of the system is controled by p actors (players) which intend to minimize their integral-time costs of sy...
详细信息
An injective k-coloring of a graph G=(V,E) is a function f:V ->{1,2,& mldr;,k} such that for every pair of vertices u and v having a common neighbor, f(u)not equal f(v). The injective chromatic number chi(i)(G)...
详细信息
An injective k-coloring of a graph G=(V,E) is a function f:V ->{1,2,& mldr;,k} such that for every pair of vertices u and v having a common neighbor, f(u)not equal f(v). The injective chromatic number chi(i)(G) of a graph G is the minimum k for which G admits an injective k-coloring. Given a graph G and a positive integer k, Decide Injective Coloring Problem is to decide whether G admits an injective k-coloring. Decide Injective Coloring Problem is known to be NP-complete for chordal graphs. In this paper, we strengthen this result by proving that Decide Injective coloring Problem remains NP-complete for undirected path graphs, a proper subclass of chordal graphs. Moreover, we show that it is not possible to approximate the injective chromatic number of an undirected path graph within a factor of n1/3-epsilon in polynomialtime for every epsilon>0 unless ZPP = NP. On the positive side, we prove that the injective chromatic number of an interval graph is either Delta(G) or Delta(G)+1, where Delta(G) is the maximum degree of G. We also characterize the interval graphs having chi(i)(G)=Delta(G) and chi(i)(G)=Delta(G)+1. As a consequence of this characterization, we obtain a linear timealgorithm to find the injective chromatic number of an interval graph.
The study of structural graph width parameters like tree-width, clique-width and rankwidth has been ongoing during the last five decades, and their algorithmic use has also been increasing (Cygan et al., 2015). New wi...
详细信息
The study of structural graph width parameters like tree-width, clique-width and rankwidth has been ongoing during the last five decades, and their algorithmic use has also been increasing (Cygan et al., 2015). New width parameters continue to be defined, for example, MIM-width in 2012, twin-width in 2020, and mixed-thinness, a generalization of thinness, in 2022. The concept of thinness of a graph was introduced in 2007 by Mannino, Oriolo, Ricci and Chandran, and it can be seen as a generalization of interval graphs, which are exactly the graphs with thinness equal to one. This concept is interesting because if a representation of a graph as a k-thin graph is given for a constant value k, then several known NP-complete problems can be solved in polynomialtime. Some examples are the maximum weighted independent set problem, solved in the seminal paper by Mannino et al., and the capacitated coloring with fixed number of colors (Bonomo, Mattia and Oriolo, 2011). In this work we present a constructive O(n log(n))-timealgorithm to compute the thinness for any given n-vertex tree, along with a corresponding thin representation. We use intermediate results of this construction to improve known bounds of the thinness of some special families of trees.
In this paper, we deal with two variants of graph matching, the graph isomorphism with restriction and the prefix set of graph isomorphism. The former problem is known to be NP-complete, whereas the latter problem is ...
详细信息
In this paper, we deal with two variants of graph matching, the graph isomorphism with restriction and the prefix set of graph isomorphism. The former problem is known to be NP-complete, whereas the latter problem is known to be GI-complete. We propose polynomialtime exact algorithms for these problems on partial k-trees.
Multi-constrained Quality-of-Service (QoS) routing is a big challenge for Mobile Ad hoc Networks (MANETs) where the topology may change constantly. In this paper a novel QoS Routing algorithm based on Simulated Anneal...
详细信息
Multi-constrained Quality-of-Service (QoS) routing is a big challenge for Mobile Ad hoc Networks (MANETs) where the topology may change constantly. In this paper a novel QoS Routing algorithm based on Simulated Annealing (SA_RA) is proposed. This algorithm first uses an energy function to translate multiple QoS weights into a single mixed metric and then seeks to find a feasible path by simulated annealing. The pa- per outlines simulated annealing algorithm and analyzes the problems met when we apply it to Qos Routing (QoSR) in MANETs. Theoretical analysis and experiment results demonstrate that the proposed method is an effective approximation algorithms showing better performance than the other pertinent algorithm in seeking the (approximate) optimal configuration within a period of polynomialtime.
暂无评论