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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Discrete & computational geometry 29 (NaN), S. 485-504 
    ISSN: 1432-0444
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract. A beautiful result of Brocker and Scheiderer on the stability index of basic closed semi-algebraic sets implies, as a very special case, that every d -dimensional polyhedron admits a representation as the set of solutions of at most d(d+1)/2 polynomial inequalities. Even in this polyhedral case, however, no constructive proof is known, even if the quadratic upper bound is replaced by any bound depending only on the dimension. Here we give, for simple polytopes, an explicit construction of polynomials describing such a polytope. The number of used polynomials is exponential in the dimension, but in the two- and three-dimensional case we get the expected number d(d+1)/2 .
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 16 (1979), S. 265-280 
    ISSN: 1436-4646
    Keywords: Linear Inequalities ; Convex Polytopes ; Facets ; Travelling Salesman Problem
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract We investigate several classes of inequalities for the symmetric travelling salesman problem with respect to their facet-defining properties for the associated polytope. A new class of inequalities called comb inequalities is derived and their number shown to grow much faster with the number of cities than the exponentially growing number of subtour-elimination constraints. The dimension of the travelling salesman polytope is calculated and several inequalities are shown to define facets of the polytope. In part II (“On the travelling salesman problem II: Lifting theorems and facets”) we prove that all subtour-elimination and all comb inequalities define facets of the symmetric travelling salesman polytope.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 33 (1985), S. 28-42 
    ISSN: 1436-4646
    Keywords: Acyclic Subgraph Problem ; Feedback Arc Set Problem ; Facets of Polyhedra ; Polynomial Time Algorithms ; Weakly Acyclic Digraphs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract The acyclic subgraph problem can be formulated as follows. Given a digraph with arc weights, find a set of arcs containing no directed cycle and having maximum total weight. We investigate this problem from a polyhedral point of view and determine several classes of facets for the associated acyclic subgraph polytope. We also show that the separation problem for the facet defining dicycle inequalities can be solved in polynomial time. This implies that the acyclic subgraph problem can be solved in polynomial time for weakly acyclic digraphs. This generalizes a result of Lucchesi for planar digraphs.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 14 (1978), S. 373-377 
    ISSN: 1436-4646
    Keywords: Nonlinear Programming ; Algorithms ; Continuous Unbounded Algorithms ; Global Convergence of Algorithms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 16 (1979), S. 281-302 
    ISSN: 1436-4646
    Keywords: Linear Inequalities ; Convex Polytopes ; Facets ; Lifting Theorems ; Travelling Salesman Problem
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract Four lifting theorems are derived for the symmetric travelling salesman polytope. They provide constructions and state conditions under which a linear inequality which defines a facet of then-city travelling salesman polytope retains its facetial property for the (n + m)-city travelling salesman polytope, wherem ≥ 1 is an arbitrary integer. In particular, they permit a proof that all subtour-elimination as well as comb inequalities define facets of the convex hull of tours of then-city travelling salesman problem, wheren is an arbitrary integer.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Computing 39 (1987), S. 327-344 
    ISSN: 1436-5057
    Keywords: 05-04 ; 05C45 ; 90C10 ; Matching ; cutting plane algorithm ; polyhedral combinatorics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Wir beschreiben die Implementierung eines Schnittebenenverfahrens zur Bestimmung minimaler gewichteter perfekter 2-Matchings. Der Algorithmus baut auf der vollständigen Beschreibung des perfekten 2-Matching-Polytops, die Edmonds angegeben hat, auf und verwendet die Simplexmethode zur Lösung der im Verfahren auftretenden LP-Relaxierungen. Schnittebenen werden entweder mit schnellen Heuristiken bestimmt, oder, falls diese nicht erfolgreich sind, mit einer effizienten und auf 2-matching-Ungleichungen abgestimmten Implementierung des Padberg-Rao-Verfahrens. Mit diesem Algorithmus konnten 2-Matching-Probleme in vollständigen Graphen mit bis zu 1000 Knoten, d. h. mit bis zu 499.500 Variablen, in weniger als einer Stunde CPU-Zeit auf einem Rechner mittlerer Leistung gelöst werden.
    Notes: Abstract We describe an implementation of a cutting plane algorithm for the minimum weight perfect 2-matching problem. This algorithm is based on Edmonds' complete description of the perfect 2-matching polytope and uses the simplex algorithm for solving the LP-relaxations coming up. Cutting planes are determined by fast heuristics, or, if these fail, by an efficient implementation of the Padberg-Rao procedure, specialized for 2-matching constraints. With this algorithm 2-matching problems on complete graphs with up to 1000 nodes (i.e., 499,500 variables) have been solved in less than 1 hour CPU time on a medium speed computer.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Annals of operations research 76 (1998), S. 1-20 
    ISSN: 1572-9338
    Keywords: telecommunication network design, survivable networks, network capacity planning, cutting plane algorithm, heuristics, routing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Notes: Abstract Given a communication demand between each pair of nodes of a network, we consider the problem of deciding what capacity to install on each edge of the network in order to minimize the building cost of the network and to satisfy a given demand between each pair of nodes. The feasible capacities that can be leased from a network provider are of a particular kind in our case. There are a few so-called basic capacities having the property that every basic capacity is an integral multiple of every smaller basic capacity. An edge can be equipped with a capacity only if it is an integer combination of the basic capacities. In addition, we treat several restrictions on the routings of the demands (length restriction, diversification) and failures of single nodes or single edges. We formulate the problem as a mixed integer linear programming problem and develop a cutting plane algorithm as well as several heuristics to solve it. We report on computational results for real-world data.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1432-5217
    Keywords: clustering problem ; design of main frame computers ; graph partitioning problem ; hypergraph partitioning problem ; integer programming ; mathematical modelling ; multiple knapsack problem
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Notes: Abstract In this paper we describe and discuss a problem that arises in the (global) design of a main frame computer. The task is to assign certain functional units to a given number of so called multi chip modules or printed circuit boards taking into account many technical constraints and minimizing a complex objective function. We describe the real world problem. A thorough mathematical modelling of all aspects of this problem results in a rather complicated integer program that seems to be hopelessly difficult — at least for the present state of integer programming technology. We introduce several relaxations of the general model, which are alsoNP-hard, but seem to be more easily accessible. The mathematical relations between the relaxations and the exact formulation of the problem are discussed as well.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical methods of operations research 49 (1999), S. 501-515 
    ISSN: 1432-5217
    Keywords: Key words: Traveling Salesman Problem ; online-algorithm ; automatic storage system
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Notes: Abstract. We report on a joint project with industry that had the aim to sequence transportation requests within an automatic storage system in such a way that the overall travel time is minimized. The manufacturing environment is such that scheduling decisions have to be made before all jobs are known. We have modeled this task as an online Asymmetric Traveling Salesman Problem (ATSP). Several heuristics for the online ATSP are compared computationally within a simulation environment to judge which should be used in practice. Compared to the priority rule used so far, the optimization package reduced the unloaded travel time by about 40%. Because of these significant savings our procedure was implemented as part of the control software for the stacker cranes of the storage systems.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical methods of operations research 41 (1995), S. 255-275 
    ISSN: 1432-5217
    Keywords: Routing in VLSI-design ; Switchbox Routing ; Steiner Tree ; Steiner Tree Packing ; Cutting Plane Algorithm
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Notes: Abstract In this paper we study the following problem, which we call the weighted routing problem. Let be given a graphG = (V, E) with non-negative edge weightsw e ∈ ℝ+ and letN,N ≥ 1, be a list of node sets. The weighted routing problem consists in finding mutually disjoint edge setsS 1,...,S N such that, for eachk ∈ {1, ...,N}, the subgraph (V(S k),S k) contains an [s, t]-path for alls, t ∈ T k and the sum of the weights of the edge sets is minimal. Our motivation for studying this problem arises from the routing problem in VLSI-design, where given sets of points have to be connected by wires. We consider the weighted routing problem from a polyhedral point of view. We define an appropriate polyhedron and try to (partially) describe this polyhedron by means of inequalities. We describe our separation algorithms for some of the presented classes of inequalities. Based on these separation routines we have implemented a branch and cut algorithm. Our algorithm is applicable to an important subclass of routing problems arising in VLSI-design, namely to switchbox routing problems where the underlying graph is a grid graph and the list of node sets is located on the outer face of the grid. We report on our computational experience with this class of problem instances.
    Type of Medium: Electronic Resource
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