We study the approximability of minimum total weighted tardiness with a modified objective which includes an additive constant. This ensures the existence of a positive lower bound for the minimum value. Moreover the ...
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We study the approximability of minimum total weighted tardiness with a modified objective which includes an additive constant. This ensures the existence of a positive lower bound for the minimum value. Moreover the new objective has a natural interpretation in just-in-time production systems. (C) 2007 Elsevier B.V. All rights reserved.
In this paper, we prove that the Max Morse Matching Problem is approximable, thus resolving an open problem posed by Joswig and Pfetsch [1]. For D-dimensional simplicial complexes, we obtain a (D+1)/(D-2+D+1)-factor a...
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In this paper, we prove that the Max Morse Matching Problem is approximable, thus resolving an open problem posed by Joswig and Pfetsch [1]. For D-dimensional simplicial complexes, we obtain a (D+1)/(D-2+D+1)-factor approximation ratio using a simple edge reorientation algorithm that removes cycles. For D >= 5, we describe a 2/D-factor approximation algorithm for simplicial manifolds by processing the simplices in increasing order of dimension. This algorithm leads to 1/2-factor approximation for 3-manifolds and 4/9-factor approximation for 4-manifolds. This algorithm may also be applied to non-manifolds resulting in a 1/(D+1)-factor approximation ratio. One application of these algorithms is towards efficient homology computation of simplicial complexes. Experiments using a prototype implementation on several datasets indicate that the algorithm computes near optimal results. (C) 2016 Elsevier B.V. All rights reserved.
We study the problems of pricing an indivisible product to consumers who are embedded in a given social network. The goal is to maximize the revenue of the seller by the so-called iterative pricing that offers consume...
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We study the problems of pricing an indivisible product to consumers who are embedded in a given social network. The goal is to maximize the revenue of the seller by the so-called iterative pricing that offers consumers a sequence of prices over time. The consumers are assumed to be impatient in that they buy the product as soon as the seller posts a price not greater than their valuations of the product. The product's value for a consumer is determined by two factors: a fixed consumer-specified intrinsic value and a variable externality that is exerted from the consumer's neighbors in a linear way. We focus on the scenario of negative externalities, which captures many interesting situations, but is much less understood in comparison with its positive externality counterpart. Assuming complete information about the network, consumers' intrinsic values, and the negative externalities, we prove that it is NP-hard to find an optimal iterative pricing, even for unweighted tree networks with uniform intrinsic values. Complementary to the hardness result, we design a 2-approximation algorithm for general weighted networks with (possibly) nonuniform intrinsic values. We show that, as an approximation to optimal iterative pricing, single pricing works fairly well for many interesting cases, such as forests, ErdAs-R,nyi networks and Barabasi-Albert networks, although its worst-case performance can be arbitrarily bad in general networks.
We consider the following two deterministic inventory optimization problems with non-stationary demands. Submodular joint replenishment problem. This involves multiple item types and a single retailer who faces demand...
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We consider the following two deterministic inventory optimization problems with non-stationary demands. Submodular joint replenishment problem. This involves multiple item types and a single retailer who faces demands over a finite planning horizon of T periods. In each time period, any subset of item-types can be ordered incurring a joint ordering cost which is submodular. Moreover, items can be held in inventory while incurring a holding cost. The objective is to find a sequence of orders that satisfies all demands and minimizes the total ordering and holding costs. Inventory routing problem. This involves a single depot that stocks items, and multiple retailer locations facing demands over a finite planning horizon of T periods. In each time period, any subset of locations can be visited using a vehicle originating from the depot. There is also cost incurred for holding items at any retailer. The objective here is to satisfy all demands while minimizing the sum of routing and holding costs. We present a unified approach that yields -factor approximation algorithms for both problems when the holding costs are polynomial functions. A special case is the classic linear holding cost model, wherein this is the first sub-logarithmic approximation ratio for either problem.
Given a weighted graph G=(V,E)with weight w:E→Z+,a k-cycle transversal is an edge subset A of E such that G−A has no *** minimum weight of kcycle transversal is the weighted transversal number on k-cycle,denoted byτ...
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Given a weighted graph G=(V,E)with weight w:E→Z+,a k-cycle transversal is an edge subset A of E such that G−A has no *** minimum weight of kcycle transversal is the weighted transversal number on k-cycle,denoted byτk(Gw).In this paper,we design a(k−1/2)-approximation algorithm for the weighted transversal number on k-cycle when k is *** a weighted graph G=(V,E)with weight w:E→Z+,a k-clique transversal is an edge subset A of E such that G−A has no *** minimum weight of k-clique transversal is the weighted transversal number on k-clique,denoted byτapproximation algorithm for the weighted transversal number on k(Gw).In this paper,we design a(k2−k−1)/***,we discuss the relationship between k-clique covering and k-clique packing in complete graph Kn.
The POWER DOMINATING SET (PDS) problem is the following extension of the well-known dominating set problem: find a smallest-size set of nodes S that power dominates all the nodes, where a node v is power dominated if ...
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The POWER DOMINATING SET (PDS) problem is the following extension of the well-known dominating set problem: find a smallest-size set of nodes S that power dominates all the nodes, where a node v is power dominated if (1) v is in S or v has a neighbor in S, or (2) v has a neighbor w such that w and all of its neighbors except v are power dominated. We show a hardness of approximation threshold of 2(log1-epsilon n) in contrast to the logarithmic hardness for the dominating set problem. We give an O(root n)-approximation algorithm for planar graphs and show that our methods cannot improve on this approximation guarantee. Finally, we initiate the study of PDS on directed graphs and show the same hardness threshold of 2(log1-epsilon n) for directed acyclic graphs. Also we show that the directed PDS problem can be solved optimally in linear time if the underlying undirected graph has bounded tree-width.
In this paper, we address the vertex-traversing-constrained mixed Chinese postman problem (the VtcMCP problem), which is a further generalization of the Chinese postman problem, and this new problem has many practical...
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In this paper, we address the vertex-traversing-constrained mixed Chinese postman problem (the VtcMCP problem), which is a further generalization of the Chinese postman problem, and this new problem has many practical applications in real life. Specifically, given a connected mixed graph G=(V,E boolean OR A;w,b)\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$G=(V, E\cup A;w,b)$$\end{document} with length function w()\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$w(\cdot )$$\end{document} on edges and arcs and traversal function b()\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$b(\cdot )$$\end{document} on vertices, we are asked to determine a tour traversing each link (i.e., either edge or arc) at least once and each vertex v at most b(v) times, the objective is to minimize the total length of such a tour, where n=|V|\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$n=|V|$$\end{document} is the number of vertices and m=|E boolean OR A|\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$m=|E\cup A|$$\end{document} is the number of links of G, respectively
Sorting by Genome Rearrangements is a classic problem in Computational Biology. Several models have been considered so far, each of them defines how a genome is modeled (for example, permutations when assuming no dupl...
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Sorting by Genome Rearrangements is a classic problem in Computational Biology. Several models have been considered so far, each of them defines how a genome is modeled (for example, permutations when assuming no duplicated genes, strings if duplicated genes are allowed, and/or use of signs on each element when gene orientation is known), and which rearrangements are allowed. Recently, a new problem, called Sorting by Multi-Cut Rearrangements, was proposed. It uses the k-cut rearrangement which cuts a permutation (or a string) at k >= 2 places and rearranges the generated blocks to obtain a new permutation (or string) of same size. This new rearrangement may model chromoanagenesis, a phenomenon consisting of massive simultaneous rearrangements. Similarly as the Double-Cut-and-Join, this new rearrangement also generalizes several genome rearrangements such as reversals, transpositions, revrevs, transreversals, and block-interchanges. In this paper, we extend a previous work based on unsigned permutations and strings to signed permutations. We show the complexity of this problem for different values of k, and that the approximation algorithm proposed for unsigned permutations with any value of k can be adapted to signed permutations. We also show a 1.5-approximation algorithm for the specific case k = 4, as well as a generic approximation algorithm applicable for any k >= 5, that always reaches constant ratio. The latter makes use of the cycle graph, a well-known structure in genome rearrangements. We implemented and tested the proposed algorithms on simulated data.
In this paper, we address the trip-constrained vehicle routing cover problem (theTcVRC problem). Specifically, given a metric complete graphG=(V,E;w)with a set D(subset of V)of depots, a setJ(=V\D)of customer location...
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In this paper, we address the trip-constrained vehicle routing cover problem (theTcVRC problem). Specifically, given a metric complete graphG=(V,E;w)with a set D(subset of V)of depots, a setJ(=V\D)of customer locations, each customerhaving unsplittable demand 1, andkvehicles with capacityQ, it is asked to find a setC={C-i|=1,2,...,k}ofktours forkvehicles to service all customers, each tourfor a vehicle starts and ends at one depot inDand permits to be replenished at someother depots inDbefore continuously servicing at mostQcustomers, i.e., the numberof customers continuously serviced in per trip of each tour is at mostQ(except thetwo end-vertices of that trip), where each trip is a path or cycle, starting at a depot andending at other depot (maybe the same depot) inD, such that there are no other depotsin the interior of that path or cycle, the objective is to minimize the maximum weightof suchktours inC, i.e., minCmax{w(C-i)|i=1,2,...,k}, wherew(Ci)is thetotal weight of edges in that tourCi. Consideringkvehicles whether to have commondepot or suppliers, we consider three variations of the TcVRC problem, i.e., (1) the trip-constrained vehicle routing cover problem with multiple suppliers (the TcVRC-MSproblem) is asked to find a setC={Ci|i=1,2,...,k}ofktours mentioned-above,the objective is to minimize the maximum weight of suchktours inC;(2) the trip-constrained vehicle routing cover problem with common depot and multiple suppliers(the TcVRC-CDMS problem) is asked to find a setC={Ci|i=1,2,...,k}ofk tours mentioned-above, where each tour starts and ends at same depotvinD, eachvehicle having its suppliers at some depots inD(possibly includingv), the objectiveis to minimize the maximum weight of suchktours inC;(3) the trip-constrainedk-traveling salesman problem with non-suppliers (the TckTS-NS problem, simply theTckTSP-NS) is asked to find a setC={C-i=1,2,...,k}of k tours mentioned-above, where each tour starts and ends at same depotvinD, each vehicle havingnon-suppli
We study the minimal decomposition of octilinear polygons with holes into octilinear triangles and rectangles. This new problem is relevant in the context of modern electronic CAD systems, where the generation and pro...
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We study the minimal decomposition of octilinear polygons with holes into octilinear triangles and rectangles. This new problem is relevant in the context of modern electronic CAD systems, where the generation and propagation of electromagnetic noise into multi layer PCBs has to be detected. It is a generalization of a problem deeply investigated: the minimal decomposition of rectilinear polygons into rectangles. We show that the new problem is NP-hard. We also show the NP-hardness of a related problem, that is the decomposition of an octilinear polygon with holes into octilinear convex polygons. For both problems, we propose efficient approximation algorithms. (C) 2019 Elsevier B.V. All rights reserved.
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