This study investigates dynamic inventory relocation to respond proactively to the changing relief demand forecasts over time. In particular, we examine how to relocate mobile inventory optimally to serve nonstationar...
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This study investigates dynamic inventory relocation to respond proactively to the changing relief demand forecasts over time. In particular, we examine how to relocate mobile inventory optimally to serve nonstationary stochastic demand at several potential disaster sites. We propose a dynamic relocation model using dynamic programming (DP) and develop both analytical and numerical results regarding optimal relocation policies, the minimum cost-to-go function, and the value of inventory mobility over traditional warehouse pre-positioning. Given the computational complexity of the backwards DP algorithm, we develop a base state heuristic (BSH) for general problems by exploiting the real-world disaster pattern of occurrence. For problems with temporally independent demand, we propose a polynomialtime exact algorithm based on a spatial-temporal graph. For problems with spatially independent demand, we design a speedup technique to implement BSH in polynomialtime. The proposed model and algorithms are further extended to consider the impact of transportation uncertainties. Numerical experiments show that the proposed algorithms return high-quality decisions only in a small fraction of the time required by an exact algorithm and a myopic algorithm. The proposed model and algorithms are applicable to any type of mobile inventory, facility, or server in similar settings.
We consider two scheduling problems on in uniform serial batch machines where m is fixed. In the first problem, all jobs have to be scheduled and the objective is to minimize total completion time. In the second probl...
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We consider two scheduling problems on in uniform serial batch machines where m is fixed. In the first problem, all jobs have to be scheduled and the objective is to minimize total completion time. In the second problem, each job may be either rejected or accepted to be scheduled and the objective is to minimize the sum of total completion time and total rejection penalty. A polynomialtime procedure is presented to solve both problems with the time complexity O (m(2)n(m+2)) and O (m(2)n(m+5)), respectively. (C) 2014 Elsevier B.V. All rights reserved.
For a graph G, let gamma : v(G) -> {1, .... vertical bar V(G)vertical bar} be a one-to-one function. The bandwidth of gamma is the maximum of vertical bar gamma (u) - gamma(v)vertical bar over uv is an element of E...
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For a graph G, let gamma : v(G) -> {1, .... vertical bar V(G)vertical bar} be a one-to-one function. The bandwidth of gamma is the maximum of vertical bar gamma (u) - gamma(v)vertical bar over uv is an element of E(C). The bandwidth of G, denoted b(G), is the minimum bandwidth over all embeddings gamma, b(G) = Min(gamma) {max{vertical bar gamma(u) - gamma(v)vertical bar : uv is an element of E(G)}}. In this paper, we show that the bandwidth computation problem for trees of diameter at most 4 can be solved in polynomialtime. This naturally complements the result computing the bandwidth for 2-caterpillars. (C) 2012 Elsevier B.V. All rights reserved.
Due to the success of the Internet and the diversity of communication applications, it is becoming increasingly difficult to forecast traffic patterns. To capture the traffic variations, we introduce a flexible model ...
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Due to the success of the Internet and the diversity of communication applications, it is becoming increasingly difficult to forecast traffic patterns. To capture the traffic variations, we introduce a flexible model where traffic belongs to a polytope. We assume that the traffic demands between nodes can be carried on many paths, with respect to network resources. Moreover, to guarantee the network stability and to make the routing easy to implement, the proportions of traffic flowing through each path have to be independent of the current traffic demands. We show that a minimum-cost routing satisfying the previous properties can be efficiently computed by column and constraint generations. We then present several strategies related to certain algorithmic details. Finally, theoretical and computational studies show that this new flexible model can be much more economical than a classical deterministic model based on a given traffic matrix. This paper can be considered as a mathematical framework for a new flexible virtual private network service offer. It also introduces a new concept: the routing of a polytope.
We study some counting and enumeration problems for chordal graphs, especially concerning independent sets. We first provide the following efficient algorithms for a chordal graph: (1) a linear-timealgorithm for coun...
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We study some counting and enumeration problems for chordal graphs, especially concerning independent sets. We first provide the following efficient algorithms for a chordal graph: (1) a linear-timealgorithm for counting the number of independent sets;(2) a linear-timealgorithm for counting the number of maximum independent sets;(3) a polynomial-timealgorithm for counting the number of independent sets of a fixed size. With similar ideas, we show that enumeration (namely, listing) of the independent sets, the maximum independent sets, and the independent sets of a fixed size in a chordal graph can be done in constant time per output. On the other hand, we prove that the following problems for a chordal graph are #P-complete: (1) counting the number of maximal independent sets;(2) counting the number of minimum maximal independent sets. With similar ideas, we also show that finding a minimum weighted maximal independent set in a chordal graph is NP-hard, and even hard to approximate. (C) 2007 Elsevier B.V. All rights reserved.
We provide a polynomial time algorithm for deciding the equation solvability problem over finite groups that are semidirect products of a p-group and an Abelian group. As a consequence, we obtain a polynomialtime alg...
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We provide a polynomial time algorithm for deciding the equation solvability problem over finite groups that are semidirect products of a p-group and an Abelian group. As a consequence, we obtain a polynomial time algorithm for deciding the equivalence problem over semidirect products of a finite nilpotent group and a finite Abelian group. The key ingredient of the proof is to represent group expressions using a special polycyclic, presentation of these finite solvable groups.
Quadratic programming problems involving distance matrix (D) that arises in trees are considered in the literature by Dankelmann (Discrete Math 312:12-20, 2012), Bapat and Neogy (Ann Oper Res 243:365-373, 2016). In th...
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Quadratic programming problems involving distance matrix (D) that arises in trees are considered in the literature by Dankelmann (Discrete Math 312:12-20, 2012), Bapat and Neogy (Ann Oper Res 243:365-373, 2016). In this paper, we consider the question of solving the quadratic programming problem of finding maximum of x(T)Rx subject to x being a nonnegative vector with sum 1 and show that for the class of simple graphs with resistance distance matrix (R) which are not necessarily a tree, this problem can be reformulated as a strictly convex quadratic programming problem. An application to symmetric bimatrix game is also presented.
This paper deals with exponential neighborhoods for combinatorial optimization problems. Exponential neighborhoods are large sets of feasible solutions whose size grows exponentially with the input length. We are espe...
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This paper deals with exponential neighborhoods for combinatorial optimization problems. Exponential neighborhoods are large sets of feasible solutions whose size grows exponentially with the input length. We are especially interested in exponential neighborhoods over which the TSP (respectively, the QAP) can be solved in polynomialtime, and we investigate combinatorial and algorithmical questions related to such neighborhoods. First, we perform a careful study of exponential neighborhoods for the TSP. We investigate neighborhoods that can be declined in a simple way via assignments, matchings in bipartite graphs, partial orders, trees and other combinatorial structures. we identify several properties of these combinatorial structures that lead to polynomialtime optimization algorithms, and we also provide variants that slightly violate these properties and lead to NP-complete optimization problems. Whereas it is relatively easy to find exponential neighborhoods over which the TSP can be solved in polynomialtime, the corresponding situation for the QAP looks pretty hopeless: Every exponential neighborhood that is considered in this paper provably lends to an NP-complete optimization problem for the QAP.
In this paper we analyze the computational complexity of system diagnosis. We show that several problems for instantaneous and sequential fault diagnosis of systems are polynomially complete and that for single-loop s...
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In this paper we analyze the computational complexity of system diagnosis. We show that several problems for instantaneous and sequential fault diagnosis of systems are polynomially complete and that for single-loop systems these problems are solvable in polynomialtime.
A simply polynomial time algorithm is given for computing the setup number, or jump number, of an ordered set with fixed width. This arises as an interesting application of a polynomial time algorithm for solving a mo...
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A simply polynomial time algorithm is given for computing the setup number, or jump number, of an ordered set with fixed width. This arises as an interesting application of a polynomial time algorithm for solving a more general weighted problem in precedence constrained scheduling.
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