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  • Articles  (20,657)
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  • Articles  (20,657)
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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 32 (1985), S. 249-277 
    ISSN: 1436-4646
    Keywords: Minisum Locations ; Location-Allocation ; Network Location ; Dynamic Location
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract In this paper, we consider multiperiod minisum location problems on networks in which demands can occur continuously on links according to a uniform probability density function. In addition, demands may change dynamically over time periods and at most one facility can be located per time period. Two types of networks are considered in conjunction with three behavioral strategies. The first type of network discussed is a chain graph. A myopic strategy and long-range strategy for locatingp-facilities are considered, as is a discounted present worth strategy for locating two facilities. Although these problems are generally nonconvex, effective methods are developed to readily identify all local and global minima. This analysis forms the basis for similar problems on tree graphs. In particular, we construct algorithms for the 3-facility myopic problem and the 2-facility long-range and discounted cost problems on a tree graph. Extensions and suggestions for further research on problems involving more general networks are provided.
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  • 2
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    Mathematical programming 32 (1985), S. 366-370 
    ISSN: 1436-4646
    Keywords: Cores ; Dual Prices ; Linear Production Games
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract Consider a game in which resources may be combined to produce products of known values. For linear production processes, the game may be characterized by a family of linear programs. It is shown that appropriately defined market prices for the resources coincide with the set of optimal dual solutions to one of these linear programs. This result generalizes and unifies the known cases in game theory, in which the core of a game coincides with the set of dual optimal solutions to a corresponding master linear programming problem.
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  • 3
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    Mathematical programming 33 (1985), S. 61-67 
    ISSN: 1436-4646
    Keywords: Conjugate Gradient Methods ; Global Convergence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract The paper examines a method of implementing an angle test for determining when to restart conjugate gradient methods in a steepest descent direction. The test is based on guaranteeing that the cosine of the angle between the search direction and the negative gradient is within a constant multiple of the cosine of the angle between the Fletcher-Reeves search direction and the negative gradient. This guarantees convergence, for the Fletcher-Reeves method is known to converge. Numerical results indicate little, if anything, is lost in efficiency, and indicate gains may well be possible for large problems.
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  • 4
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    Mathematical programming 33 (1985), S. 120-121 
    ISSN: 1436-4646
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
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  • 5
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    Mathematical programming 33 (1985), S. 93-114 
    ISSN: 1436-4646
    Keywords: Nonlinear Optimization ; Pairwise Comparison ; Priority Theory ; Fuzzy Sets ; Triangular Membership Functions ; Performance Evaluation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract In this paper we extend the deterministic performance evaluation of nonlinear optimization methods: we carry out a pairwise comparison using fuzzy estimates of the performance ratios to obtain fuzzy final scores of the methods under consideration. The key instrument is the concept of fuzzy numbers with triangular membership functions. The algebraic operations on them are simple extensions of the operations on real numbers; they are exact in the parameters (lower, modal, and upper values), not necessarily exact in the shape of the membership function. We illustrate the fuzzy performance evaluation by the ranking and rating of five methods (geometric programming and four general methods) for solving geometric-programming problems, using the results of recent computational studies. Some general methods appear to be leading, an outcome which is not only due to their performance under subjective criteria like domain of applications and conceptual simplicity of use; they also score higher under more objective criteria like robustness and efficiency.
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  • 6
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    Mathematical programming 35 (1986), S. 110-119 
    ISSN: 1436-4646
    Keywords: Convex programming ; Frank-Wolfe algorithm
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract We give a detailed proof, under slightly weaker conditions on the objective function, that a modified Frank-Wolfe algorithm based on Wolfe's ‘away step’ strategy can achieve geometric convergence, provided a strict complementarity assumption holds.
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  • 7
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    Mathematical programming 35 (1986), S. 125-125 
    ISSN: 1436-4646
    Source: Springer Online Journal Archives 1860-2000
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  • 8
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    Mathematical programming 35 (1986), S. 140-172 
    ISSN: 1436-4646
    Keywords: Probabilistic analysis ; self-dual simplex ; spherical symmetry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract In this paper we analyze the average number of steps performed by the self-dual simplex algorithm for linear programming, under the probabilistic model of spherical symmetry. The model was proposed by Smale. Consider a problem ofn variables withm constraints. Smale established that for every number of constraintsm, there is a constantc(m) such that the number of pivot steps of the self-dual algorithm,ρ(m, n), is less thanc(m)(lnn) m(m+1) . We improve upon this estimate by showing thatρ(m, n) is bounded by a function ofm only. The symmetry of the function inm andn implies thatρ(m, n) is in fact bounded by a function of the smaller ofm andn.
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  • 9
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    Mathematical programming 42 (1988), S. 363-374 
    ISSN: 1436-4646
    Keywords: Newton method ; parallel algorithms ; superlinear convergence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract A parallel Newton method is described for the minimization of a twice continuously differentiable uniformly convex functionF(x). The algorithm generates a sequence {x j } which converges superlinearly to the global minimizer ofF(x).
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  • 10
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    Mathematical programming 42 (1988), S. 489-563 
    ISSN: 1436-4646
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract Polyhedra related to matroids and sub- or supermodular functions play a central role in combinatorial optimization. The purpose of this paper is to present a unified treatment of the subject. The structure of generalized polymatroids and submodular flow systems is discussed in detail along with their close interrelation. In addition to providing several applications, we summarize many known results within this general framework.
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  • 11
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    Mathematical programming 43 (1989), S. 31-44 
    ISSN: 1436-4646
    Keywords: Affine-scaling ; Karmarkar's algorithm ; dual algorithm ; feasibility algorithm
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract The affine-scaling modification of Karmarkar's algorithm is extended to solve problems with free variables. This extended primal algorithm is used to prove two important results. First the geometrically elegant feasibility algorithm proposed by Chandru and Kochar is the same algorithm as the one obtained by appending a single column of residuals to the constraint matrix. Second the dual algorithm as first described by Adler et al., is the same as the extended primal algorithm applied to the dual.
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  • 12
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    Mathematical programming 33 (1985), S. 139-145 
    ISSN: 1436-4646
    Keywords: Computational Complexity ; NP-Complete ; Linear Program ; Polyhedron ; Cell
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract A nonempty closed convex polyhedronX can be represented either asX = {x: Ax ⩽b}, where (A, b) are given, in which caseX is called anH-cell, or in the formX = {x: x = Uλ + Vμ, Σλ j = 1,λ ⩾ 0,μ ⩾ 0}, where (U, V) are given, in which caseX is called aW-cell. This note discusses the computational complexity of certain set containment problems. The problems of determining if $$X \nsubseteq Y$$ , where (i)X is anH-cell andY is a closed solid ball, (ii)X is anH-cell andY is aW-cell, or (iii)X is a closed solid ball andY is aW-cell, are all shown to be NP-complete, essentially verifying a conjecture of Eaves and Freund. Furthermore, the problem of determining whether there exists an integer point in aW-cell is shown to be NP-complete, demonstrating that regardless of the representation ofX as anH-cell orW-cell, this integer containment problem is NP-complete.
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  • 13
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    Mathematical programming 33 (1985), S. 123-138 
    ISSN: 1436-4646
    Keywords: Set Packing ; Integer Programming ; Linear Programming ; Simplex Method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract This paper considers the set packing problem max{wx: Ax ⩽ b, x ⩾ 0 and integral}, whereA is anm × n 0–1 matrix,w is a 1 ×n weight vector of real numbers andb is anm × 1 vector of ones. In equality form, its linear programming relaxation is max{wx: (x, y) ∈P(A)} whereP(A) = {(x, y):Ax +I m y =b, x⩾0,y⩾0}. Letx 1 be any feasible solution to the set packing problem that is not optimal and lety 1 =b − Ax 1; then (x 1,y 1) is an integral extreme point ofP(A). We show that there exists a sequence of simplex pivots from (x 1,y 1) to (x*,y*), wherex* is an optimal solution to the set packing problem andy* =b − Ax*, that satisfies the following properties. Each pivot column has positive reduced weight and each pivot element equals plus one. The number of pivots equals the number of components ofx* that are nonbasic in (x 1,y 1).
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  • 14
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    Mathematical programming 45 (1989), S. 35-47 
    ISSN: 1436-4646
    Keywords: Facets ; ternary ; covering ; packing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract We consider ternary matrices, i.e., integer matrices having all entries 0, 1 or 2. Three associated problems—the group problem, covering, and packing—are studied. General classes of vertices and facets are discussed in each case. Certain lifting procedures are also described. For all three problems techniques used are natural extensions of those used in the binary case.
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  • 15
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    Mathematical programming 33 (1985), S. 1-27 
    ISSN: 1436-4646
    Keywords: Traveling Salesman Problem ; Integer Polyhedron ; Facet ; Graph ; Series-Parallel Graph ; Steiner Tree ; Polynomial Algorithm
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract Given a graphG = (N, E) and a length functionl: E → ℝ, the Graphical Traveling Salesman Problem is that of finding a minimum length cycle goingat least once through each node ofG. This formulation has advantages over the traditional formulation where each node must be visited exactly once. We give some facet inducing inequalities of the convex hull of the solutions to that problem. In particular, the so-called comb inequalities of Grötschel and Padberg are generalized. Some related integer polyhedra are also investigated. Finally, an efficient algorithm is given whenG is a series-parallel graph.
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  • 16
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    Mathematical programming 33 (1985), S. 146-161 
    ISSN: 1436-4646
    Keywords: Infinite Linear Programming ; Ordered Fields ; Extreme Points ; Extreme Directions ; Opposite Sign Property ; Nonlinear Equations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract This paper provides a characterization of extreme points and extreme directions of the subsets of the space of generalized finite sequences occurring as the constraint sets of semi-infinite or infinite linear programs. The main result is that these sets are generated by (possibly infinitely many) extreme points and extreme directions. All results are valid over arbitrary ordered fields.
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  • 17
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    Mathematical programming 33 (1985), S. 204-233 
    ISSN: 1436-4646
    Keywords: Linear Programming ; Simplex Methods ; Piecewise-Linear Programming ; Nondifferentiable Optimization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract The simplex method for linear programming can be extended to permit the minimization of any convex separable piecewise-linear objective, subject to linear constraints. This three-part paper develops and analyzes a general, computationally practical simplex algorithm for piecewiselinear programming. Part I derives and justifies the essential steps of the algorithm, by extension from the simplex method for linear programming in bounded variables. The proof employs familiar finite-termination arguments and established piecewise-linear duality theory. Part II considers the relaxation of technical assumptions pertaining to finiteness, feasibility and nondegeneracy of piecewise-linear programs. Degeneracy is found to have broader consequences than in the linear case, and the standard techniques for prevention of cycling are extended accordingly. Part III analyzes the computational requirements of piecewise-linear programming. The direct approach embodied in the piecewise-linear simplex algorithm is shown to be inherently more efficient than indirect approaches that rely on transformation of piecewise-linear programs to equivalent linear programs. A concluding section surveys the many applications of piecewise-linear programming in linear programming,l 1 estimation, goal programming, interval programming, and nonlinear optimization.
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  • 18
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    Mathematical programming 33 (1985), S. 339-351 
    ISSN: 1436-4646
    Keywords: Variational Inequality ; Nondifferentiable Optimization ; Nonconvex Programming ; Network Optimization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract The variational inequality problem in Euclidian space is formulated as a nonconvex, nondifferentiable optimization problem. We show that any stationary point is optimal, and we propose a solution algorithm that decreases the nondifferential objective monotonically. Application to the asymmetric traffic assignment problem is considered.
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  • 19
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    Mathematical programming 35 (1986), S. 17-31 
    ISSN: 1436-4646
    Keywords: Linear complementarity problem ; K-matrix ; Q 0-matrix ; finite characterization ; Q-matrix
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract The class of realn × n matricesM, known asK-matrices, for which the linear complementarity problemw − Mz = q, w ≥ 0, z ≥ 0, w T z =0 has a solution wheneverw − Mz =q, w ≥ 0, z ≥ 0 has a solution is characterized for dimensionsn 〈4. The characterization is finite and ‘practical’. Several necessary conditions, sufficient conditions, and counterexamples pertaining toK-matrices are also given. A finite characterization of completelyK-matrices (K-matrices all of whose principal submatrices are alsoK-matrices) is proved for dimensions 〈4.
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  • 20
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    Mathematical programming 42 (1988), S. 113-123 
    ISSN: 1436-4646
    Keywords: Scheduling ; large-scale 0–1 model ; variable fixing ; coefficient reduction ; special ordered sets
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract In this work an extension of the Beale-Tomlin special ordered sets is introduced that has proved to be efficient for solving certain types of open shop scheduling problems. Besides their usual characteristics, exclusivity constraints in the jobs are allowed, more general than tree-like precedence structures are considered, and semi-active schedules that cannot be labeled as non-optimal solutions may occur. The problem is formulated as a large-scale 0–1 model. Computational experience on some real-life problems is reported.
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  • 21
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    Mathematical programming 42 (1988), S. 181-187 
    ISSN: 1436-4646
    Keywords: Branch and bound ; bus crew scheduling ; integer programming ; scheduling ; set covering
    Source: Springer Online Journal Archives 1860-2000
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  • 22
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    Mathematical programming 42 (1988), S. 203-243 
    ISSN: 1436-4646
    Keywords: Network flows ; relaxation ; distributed algorithms ; complexity ; asynchronous algorithms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract We review a class of recently-proposed linear-cost network flow methods which are amenable to distributed implementation. All the methods in the class use the notion ofε-complementary slackness, and most do not explicitly manipulate any “global” objects such as paths, trees, or cuts. Interestingly, these methods have stimulated a large number of newserial computational complexity results. We develop the basic theory of these methods and present two specific methods, theε-relaxation algorithm for the minimum-cost flow problem, and theauction algorithm for the assignment problem. We show how to implement these methods with serial complexities of O(N 3 logNC) and O(NA logNC), respectively. We also discuss practical implementation issues and computational experience to date. Finally, we show how to implementε-relaxation in a completely asynchronous, “chaotic” environment in which some processors compute faster than others, some processors communicate faster than others, and there can be arbitrarily large communication delays.
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  • 23
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    Mathematical programming 42 (1988), S. 307-325 
    ISSN: 1436-4646
    Keywords: Full discretization ; computerized tomography ; image reconstruction ; radiotherapy treatment planning ; block-iterative algorithms ; parallel computations ; Cimmino's algorithm ; entropy maximization ; classification of algorithms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract Some row-action algorithms which exploit special objective function and constraints structure have proven advantageous for solving huge and sparse feasibility or optimization problems. Recently developed block-iterative versions of such special-purpose methods enable parallel computation when the underlying problem is appropriately decomposed. This opens the door for parallel computation in image reconstruction problems of computerized tomography and in the inverse problem of radiation therapy treatment planning, all in their fully discretized modelling approach. Since there is more than one way of deriving block-iterative versions of any row-action method, the choice has to be made with reference to the underlying real-world problem.
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  • 24
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    Mathematical programming 42 (1988), S. 391-405 
    ISSN: 1436-4646
    Keywords: Linear programming ; large-scale-systems ; decomposition ; parallel computing
    Source: Springer Online Journal Archives 1860-2000
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    Notes: Abstract This paper describes DECOMPAR: an implementation of the Dantzig-Wolfe decomposition algorithm for block-angular linear programs using parallel processing of the subproblems. The software is based on a robust experimental code for LP decomposition and runs on the CRYSTAL multicomputer at the University of Wisconsin-Madison. Initial computational experience is reported. Promising directions in future development of this approach are discussed.
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  • 25
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    Mathematical programming 42 (1988), S. 471-487 
    ISSN: 1436-4646
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    Notes: Abstract We address the problem of finding a minimum weight baseB of a matroid when, in addition, each element of the matroid is colored with one ofm colors and there are upper and lower bound restrictions on the number of elements ofB with colori, fori = 1, 2,⋯,m. This problem is a special case of matroid intersection. We present an algorithm that exploits the special structure, and we apply it to two optimization problems on graphs. When applied to the weighted bipartite matching problem, our algorithm has complexity O(|E∥V|+|V| 2log|V|). HereV denotes the node set of the underlying bipartite graph, andE denotes its edge set. The second application is defined on a general connected graphG = (V,E) whose edges have a weight and a color. One seeks a minimum weight spanning tree with upper and lower bound restrictions on the number of edges with colori in the tree, for eachi. Our algorithm for this problem has complexity O(|E∥V|+m 2 |V|+ m|V| 2). A special case of this constrained spanning tree problem occurs whenV * is a set of pairwise nonadjacent nodes ofG. One must find a minimum weight spanning tree with upper and lower bound restrictions on the degree of each node ofV *. Then the complexity of our algorithm is O(|V∥E|+|V * ∥V| 2). Finally, we discuss a new relaxation of the traveling salesman problem.
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  • 26
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    Mathematical programming 45 (1989), S. 407-435 
    ISSN: 1436-4646
    Keywords: 49D05 ; 65K05 ; Conjugate gradient ; diagonal updates ; Hilbert spaces ; large-scale problems ; limited memory ; numerical experiments ; unconstrained optimization ; variable-metric algorithms ; variablestorage
    Source: Springer Online Journal Archives 1860-2000
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    Notes: Abstract This paper describes some numerical experiments with variable-storage quasi-Newton methods for the optimization of some large-scale models (coming from fluid mechanics and molecular biology). In addition to assessing these kinds of methods in real-life situations, we compare an algorithm of A. Buckley with a proposal by J. Nocedal. The latter seems generally superior, provided that careful attention is given to some nontrivial implementation aspects, which concern the general question of properly initializing a quasi-Newton matrix. In this context, we find it appropriate to use a diagonal matrix, generated by an update of the identity matrix, so as to fit the Rayleigh ellipsoid of the local Hessian in the direction of the change in the gradient. Also, a variational derivation of some rank one and rank two updates in Hilbert spaces is given.
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  • 27
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    Mathematical programming 45 (1989), S. 529-546 
    ISSN: 1436-4646
    Keywords: Nonlinear optimization ; parallel computing ; block iterative methods ; truncated-Newton methods
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract Truncated-Newton methods are a class of optimization methods suitable for large scale problems. At each iteration, a search direction is obtained by approximately solving the Newton equations using an iterative method. In this way, matrix costs and second-derivative calculations are avoided, hence removing the major drawbacks of Newton's method. In this form, the algorithms are well-suited for vectorization. Further improvements in performance are sought by using block iterative methods for computing the search direction. In particular, conjugate-gradient-type methods are considered. Computational experience on a hypercube computer is reported, indicating that on some problems the improvements in performance can be better than that attributable to parallelism alone.
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    Mathematical programming 68 (1995), S. 105-130 
    ISSN: 1436-4646
    Keywords: primary 49B34 ; secondary 90C31 ; 93C30 ; Variational inequalities ; Sensitivity analysis ; Generalized Jacobian
    Source: Springer Online Journal Archives 1860-2000
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    Notes: Abstract Optimization problems with variational inequality constraints are converted to constrained minimization of a local Lipschitz function. To this minimization a non-differentiable optimization method is used; the required subgradients of the objective are computed by means of a special adjoint equation. Besides tests with some academic examples, the approach is applied to the computation of the Stackelberg—Cournot—Nash equilibria and to the numerical solution of a class of quasi-variational inequalities.
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    Mathematical programming 69 (1995), S. 1-43 
    ISSN: 1436-4646
    Keywords: Mathematical programming ; Cutting planes ; Analytic center
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    Notes: Abstract Anoracle for a convex setS ⊂ ℝ n accepts as input any pointz in ℝ n , and ifz ∈S, then it returns ‘yes’, while ifz ∉S, then it returns ‘no’ along with a separating hyperplane. We give a new algorithm that finds a feasible point inS in cases where an oracle is available. Our algorithm uses the analytic center of a polytope as test point, and successively modifies the polytope with the separating hyperplanes returned by the oracle. The key to establishing convergence is that hyperplanes judged to be ‘unimportant’ are pruned from the polytope. If a ball of radius 2−L is contained inS, andS is contained in a cube of side 2 L+1, then we can show our algorithm converges after O(nL 2) iterations and performs a total of O(n 4 L 3+TnL 2) arithmetic operations, whereT is the number of arithmetic operations required for a call to the oracle. The bound is independent of the number of hyperplanes generated in the algorithm. An important application in which an oracle is available is minimizing a convex function overS.
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    Mathematical programming 69 (1995), S. 45-73 
    ISSN: 1436-4646
    Keywords: Cutting plane ; Stochastic programming ; Analytic center ; Interior-point method
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    Notes: Abstract The stochastic linear programming problem with recourse has a dual block-angular structure. It can thus be handled by Benders' decomposition or by Kelley's method of cutting planes; equivalently the dual problem has a primal block-angular structure and can be handled by Dantzig-Wolfe decomposition—the two approaches are in fact identical by duality. Here we shall investigate the use of the method of cutting planes from analytic centers applied to similar formulations. The only significant difference form the aforementioned methods is that new cutting planes (or columns, by duality) will be generated not from the optimum of the linear programming relaxation, but from the analytic center of the set of localization.
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    Mathematical programming 69 (1995), S. 237-253 
    ISSN: 1436-4646
    Keywords: Variational inequality ; Nonlinear complementarity ; Nonlinear programming ; Continuation method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract This paper presents a continuation method for monotone variational inequality problems based on a new smooth equation formulation. The existence, uniqueness and limiting behavior of the path generated by the method are analyzed.
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    Mathematical programming 69 (1995), S. 269-309 
    ISSN: 1436-4646
    Keywords: Quadratic programming ; Submodular constraints ; Kuhn-Tucker conditions ; Lexicographically optimal flow ; Parametric maximum flow
    Source: Springer Online Journal Archives 1860-2000
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    Notes: Abstract We present new strongly polynomial algorithms for special cases of convex separable quadratic minimization over submodular constraints. The main results are: an O(NM log(N 2/M)) algorithm for the problemNetwork defined on a network onM arcs andN nodes; an O(n logn) algorithm for thetree problem onn variables; an O(n logn) algorithm for theNested problem, and a linear time algorithm for theGeneralized Upper Bound problem. These algorithms are the best known so far for these problems. The status of the general problem and open questions are presented as well.
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    Mathematical programming 69 (1995), S. 335-349 
    ISSN: 1436-4646
    Keywords: Polyhedral combinatorics ; Valid inequalities ; Travelling salesman ; Worst-case analysis
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    Notes: Abstract We consider most of the known classes of valid inequalities for the graphical travelling salesman polyhedron and compute the worst-case improvement resulting from their addition to the subtour polyhedron. For example, we show that the comb inequalities cannot improve the subtour bound by a factor greater than 10/9. The corresponding factor for the class of clique tree inequalities is 8/7, while it is 4/3 for the path configuration inequalities.
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    Mathematical programming 70 (1995), S. 1-16 
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    Keywords: Stochastic programming ; Polyhedral functions ; Simplicial functions
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    Notes: Abstract A dual method is presented to solve a linearly constrained optimization problem with convex, polyhedral objective function, along with a fast bounding technique, for the optimum value. The method can be used to solve problems, obtained from LPs, where some of the constraints are not required to be exactly satisfied but are penalized by piecewise linear functions, which are added to the objective function of the original problem. The method generalizes an earlier solution technique developed by Prékopa (1990). Applications to stochastic programming are also presented.
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    Mathematical programming 70 (1995), S. 107-122 
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    Keywords: Linear complementarity problem ; Predictor—corrector algorithm ; Complexity analysis ; Central trajectory ; Curvature integral ; Interior-point methods
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    Notes: Abstract In this paper, we propose a predictor—corrector-type algorithm for solving the linear complementarity problem (LCP), and prove that the actual number of iterations needed by the algorithm is bounded from above and from below by a curvature integral along the central trajectory of the problem. This curvature integral is not greater than, and possibly smaller than, the best upper bound obtained in the literature to date.
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    Mathematical programming 70 (1995), S. 159-172 
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    Keywords: Parametric nonlinear programming ; Directional differentiability ; B-derivative ; Piecewise smooth function ; Nonunique multipliers ; Degeneracy
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    Notes: Abstract Consider a parametric nonlinear optimization problem subject to equality and inequality constraints. Conditions under which a locally optimal solution exists and depends in a continuous way on the parameter are well known. We show, under the additional assumption of constant rank of the active constraint gradients, that the optimal solution is actually piecewise smooth, hence B-differentiable. We show, for the first time to our knowledge, a practical application of quadratic programming to calculate the directional derivative in the case when the optimal multipliers are not unique.
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    Mathematical programming 70 (1995), S. 191-200 
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    Keywords: Strictly pseudomonotone map ; Z-map ; Complementarity problem ; Least element problem
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    Notes: Abstract Strictly pseudomonotoneZ-maps operating on Banach lattices are considered. Equivalence of complementarity problems and least-element problems is established under certain regularity and growth conditions. This extends a recent result by Riddell (1981) for strictly monotoneZ-maps to the pseudomonotone case. Some other problems equivalent to the above are discussed as well.
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    Mathematical programming 70 (1995), S. 251-277 
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    Keywords: Linear programming ; Barrier methods ; Interior-point methods
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    Notes: Abstract Many interior-point methods for linear programming are based on the properties of the logarithmic barrier function. After a preliminary discussion of the convergence of the (primal) projected Newton barrier method, three types of barrier method are analyzed. These methods may be categorized as primal, dual and primal—dual, and may be derived from the application of Newton's method to different variants of the same system of nonlinear equations. A fourth variant of the same equations leads to a new primal—dual method. In each of the methods discussed, convergence is demonstrated without the need for a nondegeneracy assumption or a transformation that makes the provision of a feasible point trivial. In particular, convergence is established for a primal—dual algorithm that allows a different step in the primal and dual variables and does not require primal and dual feasibility. Finally, a new method for treating free variables is proposed.
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    Keywords: Linear programming ; Mixed-integer programming ; Large-scale optimization ; Airline fleet assignment
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    Notes: Abstract Given a flight schedule and set of aircraft, the fleet assignment problem is to determine which type of aircraft should fly each flight segment. This paper describes a basic daily, domestic fleet assignment problem and then presents chronologically the steps taken to solve it efficiently. Our model of the fleet assignment problem is a large multi-commodity flow problem with side constraints defined on a time-expanded network. These problems are often severely degenerate, which leads to poor performance of standard linear programming techniques. Also, the large number of integer variables can make finding optimal integer solutions difficult and time-consuming. The methods used to attack this problem include an interior-point algorithm, dual steepest edge simplex, cost perturbation, model aggregation, branching on set-partitioning constraints and prioritizing the order of branching. The computational results show that the algorithm finds solutions with a maximum optimality gap of 0.02% and is more than two orders of magnitude faster than using default options of a standard LP-based branch-and-bound code.
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    Mathematical programming 71 (1995), S. 77-100 
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    Keywords: Convex linearly constrained problems ; Variational inequalities ; Interior methods ; Entropy-like proximal method ; Maximal monotone operator
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    Notes: Abstract In this paper, an entropy-like proximal method for the minimization of a convex function subject to positivity constraints is extended to an interior algorithm in two directions. First, to general linearly constrained convex minimization problems and second, to variational inequalities on polyhedra. For linear programming, numerical results are presented and quadratic convergence is established.
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    Mathematical programming 71 (1995), S. 29-50 
    ISSN: 1436-4646
    Keywords: Max-cut ; Cut polytope ; Metric polytope ; Linear relaxation ; One-third-integrality ; Box one-third-integrality ; Forbidden minor
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    Notes: Abstract Given a graphG = (V, E), the metric polytopeS (G) is defined by the inequalitiesx(F) − x(C∖F) ⩽ |F| − 1 for $$F \subseteq C$$ , |F| odd,C cycle ofG, and 0 ⩽x e ⩽ 1 fore ∈ E. Optimization overS (G) provides an approximation for the max-cut problem. The graphG is called 1/d-integral if all the vertices ofS(G) have their coordinates in{i/d ∣ 0 ⩽ i ⩽ d}. We prove that the class of 1/d-integral graphs is closed under minors, and we present several minimal forbidden minors for 1/3-integrality. In particular, we characterize the 1/3-integral graphs on seven nodes. We study several operations preserving 1/d-integrality, in particular, thek-sum operation for 0 ⩽k ⩽ 3. We prove that series parallel graphs are characterized by the following stronger property. All vertices of the polytopeS (G) ∩ {x ∣ ℓ ⩽ x ⩽ u} are 1/3-integral for every choice of 1/3-integral boundsℓ, u on the edges ofG.
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    Mathematical programming 71 (1995), S. 101-112 
    ISSN: 1436-4646
    Keywords: Minmax ; Maximal covering problems ; Multi criteria decision-making
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    Notes: Abstract In this paper we introduce the parametric minquantile problem, a weighted generalisation ofkth maximum minimisation. It is shown that, under suitable quasiconvexity assumptions, its resolution can be reduced to solving a polynomial number of minmax problems. It is also shown how this simultaneously solves (parametric) maximal covering problems. It follows that bicriteria problems, where the aim is to both maximize the covering and minimize the cover-level, are reducible to a discrete problem, on which any multiple criteria method may be applied.
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    Mathematical programming 71 (1995), S. 71-76 
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    Keywords: Location theory ; Fermat—Weber problem ; Weiszfeld's iterative algorithm
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    Notes: Abstract The Fermat—Weber location problem requires finding a point in ℝ N that minimizes the sum of weighted Euclidean distances tom given points. A one-point iterative method was first introduced by Weiszfeld in 1937 to solve this problem. Since then several research articles have been published on the method and generalizations thereof. Global convergence of Weiszfeld's algorithm was proven in a seminal paper by Kuhn in 1973. However, since them given points are singular points of the iteration functions, convergence is conditional on none of the iterates coinciding with one of the given points. In addressing this problem, Kuhn concluded that whenever them given points are not collinear, Weiszfeld's algorithm will converge to the unique optimal solution except for a denumerable set of starting points. As late as 1989, Chandrasekaran and Tamir demonstrated with counter-examples that convergence may not occur for continuous sets of starting points when the given points are contained in an affine subspace of ℝ N . We resolve this open question by proving that Weiszfeld's algorithm converges to the unique optimal solution for all but a denumerable set of starting points if, and only if, the convex hull of the given points is of dimensionN.
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    Mathematical programming 71 (1995), S. 153-177 
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    Keywords: Network optimization ; Assignment problem ; Algorithms ; Experimental evaluation ; Cost scaling
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    Notes: Abstract The cost scaling push-relabel method has been shown to be efficient for solving minimum-cost flow problems. In this paper we apply the method to the assignment problem and investigate implementations of the method that take advantage of assignment's special structure. The results show that the method is very promising for practical use.
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    Mathematical programming 71 (1995), S. 195-206 
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    Keywords: Superfluous matrix ; Linear complementarity problem
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    Notes: Abstract Superfluous matrices were introduced by Howe (1983) in linear complementarity. In general, producing examples of this class is tedious (a few examples can be found in Chapter 6 of Cottle, Pang and Stone (1992)). To overcome this problem, we define a new class of matrices $$\bar Z$$ and establish that in $$\bar Z$$ superfluous matrices of any ordern ⩾ 4 can easily be constructed. For every integerk, an example of a superfluous matrix of degreek is exhibited in the end.
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    Mathematical programming 71 (1995), S. 249-258 
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    Keywords: Combinatorial optimization ; Integrality of polyhedra ; Generalized set packing ; Covering
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    Notes: Abstract A 0, ±1-matrixA is balanced if, in every submatrix with two nonzero entries per row and column, the sum of the entries is a multiple of four. This definition was introduced by Truemper (1978) and generalizes the notion of a balanced 0, 1-matrix introduced by Berge (1970). In this paper, we extend a bicoloring theorem of Berge (1970) and total dual integrality results of Fulkerson, Hoffman and Oppenheim (1974) to balanced 0, ±1-matrices.
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    Mathematical programming 71 (1995), S. 369-370 
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    Keywords: Local Lipschitz property ; Infinite-dimensional Hilbert space
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    Notes: Abstract An oversight in a paper of Correa and Lemaréchal (this journal, 1993) is noted; a counterexample is given.
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    Mathematical programming 80 (1998), S. 17-33 
    ISSN: 1436-4646
    Keywords: Dual simplex method ; Maximum flow ; Strongly polynomial ; Preflow algorithm ; Valid distance labels
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    Notes: Abstract This paper presents dual network simplex algorithms that require at most 2nm pivots and O(n 2 m) time for solving a maximum flow problem on a network ofn nodes andm arcs. Refined implementations of these algorithms and a related simplex variant that is not strictly speaking a dual simplex algorithm are shown to have a complexity of O(n 3). The algorithms are based on the concept of apreflow and depend upon the use of node labels that are underestimates of the distances from the nodes to the sink node in the extended residual graph associated with the current flow. © 1998 The Mathematical Programming Society, Inc. Published by Elsevier Science B.V.
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    Mathematical programming 80 (1998), S. 35-61 
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    Keywords: Graph partitioning ; Linear programming ; Bundle method ; Parallel optimization
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    Notes: Abstract This paper describes heuristics for partitioning a generalM × N matrix into arrowhead form. Such heuristics are useful for decomposing large, constrained, optimization problems into forms that are amenable to parallel processing. The heuristics presented can be easily implemented using publicly available graph partitioning algorithms. The application of such techniques for solving large linear programs is described. Extensive computational results on the effectiveness of our partitioning procedures and their usefulness for parallel optimization are presented. © 1998 The Mathematical Programming Society, Inc. Published by Elsevier Science B.V.
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    Mathematical programming 80 (1998), S. 129-160 
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    Keywords: Semidefinite programming ; Infeasible-interior-point method ; Predictor—correctormethod ; Superlinear convergence ; Primal—dual nondegeneracy
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    Notes: Abstract An example of an SDP (semidefinite program) exhibits a substantial difficulty in proving the superlinear convergence of a direct extension of the Mizuno—Todd—Ye type predictor—corrector primal-dual interior-point method for LPs (linear programs) to SDPs, and suggests that we need to force the generated sequence to converge to a solution tangentially to the central path (or trajectory). A Mizuno—Todd—Ye type predictor—corrector infeasible-interior-point algorithm incorporating this additional restriction for monotone SDLCPs (semidefinite linear complementarity problems) enjoys superlinear convergence under strict complementarity and nondegeneracy conditions. © 1998 The Mathematical Programming Society, Inc. Published by Elsevier Science B.V.
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    Mathematical programming 80 (1998), S. 161-169 
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    Keywords: Variational inequalities ; Complementarity problems ; Walrasian equilibrium ; Computational general equilibrium
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    Notes: Abstract This paper explains a method by which the number of variables in a variational inequality having a certain form can be substantially reduced by changing the set over which the variational inequality is posed. The method applies in particular to certain economic equilibrium problems occurring in applications. We explain and justify the method, and give examples of its application, including a numerical example in which the solution time for the reduced problem was approximately 2% of that for the problem in its original form. © 1998 The Mathematical Programming Society, Inc. Published by Elsevier Science B.V.
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    Mathematical programming 81 (1998), S. 201-214 
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    Keywords: Integer programming ; Cutting planes ; Cover inequalities ; Lifting ; Gomory mixed integer cuts ; Cut-and-branch
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    Notes: Abstract We investigate the use of cutting planes for integer programs with general integer variables. We show how cutting planes arising from knapsack inequalities can be generated and lifted as in the case of 0–1 variables. We also explore the use of Gomory's mixed-integer cuts. We address both theoretical and computational issues and show how to embed these cutting planes in a branch-and-bound framework. We compare results obtained by using our cut generation routines in two existing systems with a commercially available branch-and-bound code on a range of test problems arising from practical applications. © 1998 The Mathematical Programming Society, Inc. Published by Elsevier Science B.V.
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    Mathematical programming 81 (1998), S. 229-256 
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    Keywords: Branch-and-cut algorithm ; Clustering ; Compiler design ; Equipartitioning ; Finite element method ; Graph partitioning ; Layout of electronic circuits ; Separation heuristics
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    Notes: Abstract In this paper we consider the problem ofk-partitioning the nodes of a graph with capacity restrictions on the sum of the node weights in each subset of the partition, and the objective of minimizing the sum of the costs of the edges between the subsets of the partition. Based on a study of valid inequalities, we present a variety of separation heuristics for cycle, cycle with ears, knapsack tree and path-block cycle inequalities among others. The separation heuristics, plus primal heuristics, have been implemented in a branch-and-cut routine using a formulation including variables for the edges with nonzero costs and node partition variables. Results are presented for three classes of problems: equipartitioning problems arising in finite element methods and partitioning problems associated with electronic circuit layout and compiler design. © 1998 The Mathematical Programming Society, Inc. Published by Elsevier Science B.V.
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    Mathematical programming 81 (1998), S. 327-347 
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    Keywords: Convex composite function ; Second-order global optimality ; Second-order duality ; Variational inequality
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    Notes: Abstract In recent years second-order sufficient conditions of an isolated local minimizer for convex composite optimization problems have been established. In this paper, second-order optimality conditions are obtained of aglobal minimizer for convex composite problems with a non-finite valued convex function and a twice strictly differentiable function by introducing a generalized representation condition. This result is applied to a minimization problem with a closed convex set constraint which is shown to satisfy the basic constraint qualification. In particular, second-order necessary and sufficient conditions of a solution for a variational inequality problem with convex composite inequality constraints are obtained. © 1998 The Mathematical Programming Society, Inc. Published by Elsevier Science B.V.
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    Mathematical programming 82 (1998), S. 1-1 
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    Mathematical programming 82 (1998), S. 3-12 
    ISSN: 1436-4646
    Keywords: Symmetric submodular function minimization ; Submodular function minimization ; Symmetric submodular functions ; Submodular functions ; Submodular systems
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    Notes: Abstract We describe a purely combinatorial algorithm which, given a submodular set functionf on a finite setV, finds a nontrivial subsetA ofV minimizingf[A] + f[V ∖ A]. This algorithm, an extension of the Nagamochi—Ibaraki minimum cut algorithm as simplified by Stoer and Wagner [M. Stoer, F. Wagner, A simple min cut algorithm, Proceedings of the European Symposium on Algorithms ESA '94, LNCS 855, Springer, Berlin, 1994, pp. 141–147] and by Frank [A. Frank, On the edge-connectivity algorithm of Nagamochi and Ibaraki, Laboratoire Artémis, IMAG, Université J. Fourier, Grenbole, 1994], minimizes any symmetric submodular function using O(|V|3) calls to a function value oracle. © 1998 The Mathematical Programming Society, Inc. Published by Elsevier Science B.V.
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    Mathematical programming 82 (1998), S. 41-81 
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    Keywords: Random sampling ; Greedy algorithm ; Matroid basis ; Matroid partitioning
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    Notes: Abstract Random sampling is a powerful tool for gathering information about a group by considering only a small part of it. We discuss some broadly applicable paradigms for using random sampling in combinatorial optimization, and demonstrate the effectiveness of these paradigms for two optimization problems on matroids: finding an optimum matroid basis and packing disjoint matroid bases. Application of these ideas to the graphic matroid led to fast algorithms for minimum spanning trees and minimum cuts. An optimum matroid basis is typically found by agreedy algorithm that grows an independent set into an optimum basis one element at a time. This continuous change in the independent set can make it hard to perform the independence tests needed by the greedy algorithm. We simplify matters by using sampling to reduce the problem of finding an optimum matroid basis to the problem of verifying that a givenfixed basis is optimum, showing that the two problems can be solved in roughly the same time. Another application of sampling is to packing matroid bases, also known as matroid partitioning. Sampling reduces the number of bases that must be packed. We combine sampling with a greedy packing strategy that reduces the size of the matroid. Together, these techniques give accelerated packing algorithms. We give particular attention to the problem of packing spanning trees in graphs, which has applications in network reliability analysis. Our results can be seen as generalizing certain results from random graph theory. The techniques have also been effective for other packing problems. © 1998 The Mathematical Programming Society, Inc. Published by Elsevier Science B.V.
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    Keywords: Quadratic assignment ; Special cases ; Polynomially solvable ; Anti-Monge matrices ; Toeplitz matrices
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    Notes: Abstract This paper investigates a restricted version of the Quadratic Assignment Problem (QAP), where one of the coefficient matrices is an Anti-Monge matrix with non-decreasing rows and columns and the other coefficient matrix is a symmetric Toeplitz matrix. This restricted version is called the Anti-Monge—Toeplitz QAP. There are three well-known combinatorial problems that can be modeled via the Anti-Monge—Toeplitz QAP: (Pl) The “Turbine Problem”, i.e. the assignment of given masses to the vertices of a regular polygon such that the distance of the center of gravity of the resulting system to the center of the polygon is minimized. (P2) The Traveling Salesman Problem on symmetric Monge distance matrices. (P3) The arrangement of data records with given access probabilities in a linear storage medium in order to minimize the average access time. We identify conditions on the Toeplitz matrixB that lead to a simple solution for the Anti-Monge—Toeplitz QAP: The optimal permutation can be given in advance without regarding the numerical values of the data. The resulting theorems generalize and unify several known results on problems (P1), (P2), and (P3). We also show that the Turbine Problem is NP-hard and consequently, that the Anti-Monge—Toeplitz QAP is NP-hard in general. © 1998 The Mathematical Programming Society, Inc. Published by Elsevier Science B.V.
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    Mathematical programming 85 (1999), S. 135-156 
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    Keywords: Key words: bound constrained quadratic programming – Huber’s M–estimator – condition estimation – Newton iteration – factorization update
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    Notes: 1 , the smallest eigenvalue of a symmetric, positive definite matrix, and is solved by Newton iteration with line search. The paper describes the algorithm and its implementation including estimation of λ1, how to get a good starting point for the iteration, and up- and downdating of Cholesky factorization. Results of extensive testing and comparison with other methods for constrained QP are given.
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    Mathematical programming 85 (1999), S. 35-49 
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    Keywords: Key words: bimatrix game – quasi-strict equilibrium ; Mathematics Subject Classification (1991): 90D05
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    Mathematical programming 85 (1999), S. 107-134 
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    Keywords: Key words: equilibrium constraints – variational inequality problems – strong monotonicity – optimality conditions – global convergence ; Mathematics Subject Classification (1991): 90C30, 90C33, 65K05
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    Mathematical programming 85 (1999), S. 363-377 
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    Notes: 1 ,...,Am are true, then at least ℓ of the propositions B1,...,Bn are true. The main result of the paper is that the procedure in fact provides a convex hull description.
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    Keywords: Key words: maximum-entropy sampling – branch and bound – nonlinear programming
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    Mathematical programming 85 (1999), S. 259-276 
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    Keywords: Key words: linear complementary problems – Q-matrices – polyhedral combinatorics – triangulations of point configurations – 0-1 polytopes
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    Notes: T (Mx+q)=0, Mx+q≥0, x≥0 has a solution. We explain how one can use the polyhedral structure of the set of all triangulations of a finite point set to determine if an n×n matrix M is a Q-matrix. Our implementation of the algorithm is practical for deciding the Q-nature for all M with n≤8.
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    Mathematical programming 85 (1999), S. 593-616 
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    Keywords: Key words: concave optimization – conical algorithms –ω-subdivisions Mathematics Subject Classification (1991): 90C26, 65K05
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    Notes: Abstract. In this paper the problem of finding the global optimum of a concave function over a polytope is considered. A well-known class of algorithms for this problem is the class of conical algorithms. In particular, the conical algorithm based on the so called ω-subdivision strategy is considered. It is proved that, for any given accuracy ε〉0, this algorithm stops in a finite time by returning an ε-optimal solution for the problem, while it is convergent for ε=0.
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    Mathematical programming 85 (1999), S. 439-467 
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    Keywords: Mathematics Subject Classification (1991): 90C11
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    Notes: Abstract. We investigate strong inequalities for mixed 0-1 integer programs derived from flow cover inequalities. Flow cover inequalities are usually not facet defining and need to be lifted to obtain stronger inequalities. However, because of the sequential nature of the standard lifting techniques and the complexity of the optimization problems that have to be solved to obtain lifting coefficients, lifting of flow cover inequalities is computationally very demanding. We present a computationally efficient way to lift flow cover inequalities based on sequence independent lifting techniques and give computational results that show the effectiveness of our lifting procedures.
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    Mathematical programming 85 (1999), S. 525-540 
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    Keywords: Key words: semidefinite programming – perturbation theory – Kantorovi theory – condition number Mathematics Subject Classification (1991): 90C31, 90C25, 90C05
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    Notes: theory. This approach also quantifies the size of permissible perturbations. We include a discussion of these results for block diagonal semidefinite programs, of which linear programming is a special case.
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    Mathematical programming 86 (1999), S. 219-223 
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    Keywords: Key words: linear programming – computational complexity – complexity measure Mathematics Subject Classification (1991): 90C05, 90C60, 68Q25
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    Notes: Abstract. Given an m×n integer matrix A of full row rank, we consider the problem of computing the maximum of ∥B -1 A∥2 where B varies over all bases of A. This quantity appears in various places in the mathematical programming literature. More recently, logarithm of this number was the determining factor in the complexity bound of Vavasis and Ye’s primal-dual interior-point algorithm. We prove that the problem of approximating this maximum norm, even within an exponential (in the dimension of A) factor, is NP-hard. Our proof is based on a closely related result of L. Khachiyan [1].
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  • 69
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    Keywords: Key words: non-interior point method – complementarity problem – smoothing function – homotopy method
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    Notes: Abstract. We propose a class of non-interior point algorithms for solving the complementarity problems(CP): Find a nonnegative pair (x,y)∈ℝ 2n satisfying y=f(x) and x i y i =0 for every i∈{1,2,...,n}, where f is a continuous mapping from ℝ n to ℝ n . The algorithms are based on the Chen-Harker-Kanzow-Smale smoothing functions for the CP, and have the following features; (a) it traces a trajectory in ℝ 3n which consists of solutions of a family of systems of equations with a parameter, (b) it can be started from an arbitrary (not necessarily positive) point in ℝ 2n in contrast to most of interior-point methods, and (c) its global convergence is ensured for a class of problems including (not strongly) monotone complementarity problems having a feasible interior point. To construct the algorithms, we give a homotopy and show the existence of a trajectory leading to a solution under a relatively mild condition, and propose a class of algorithms involving suitable neighborhoods of the trajectory. We also give a sufficient condition on the neighborhoods for global convergence and two examples satisfying it.
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    Mathematical programming 86 (1999), S. 41-50 
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    Keywords: Key words: resolvent method – proximal point method – bundle method – bundle-trust region method – subgradient Mathematics Subject Classification (1991): 90C25, 49M45
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    Notes: Abstract. This paper establishes a linear convergence rate for a class of epsilon-subgradient descent methods for minimizing certain convex functions on ℝ n . Currently prominent methods belonging to this class include the resolvent (proximal point) method and the bundle method in proximal form (considered as a sequence of serious steps). Other methods, such as a variant of the proximal point method given by Correa and Lemaréchal, can also fit within this framework, depending on how they are implemented. The convex functions covered by the analysis are those whose conjugates have subdifferentials that are locally upper Lipschitzian at the origin, a property generalizing classical regularity conditions.
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    Mathematical programming 86 (1999), S. 387-415 
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    Keywords: Key words: semi-infinite optimization – reduction approach – stationary point – strong stability – extended Mangasarian-Fromovitz constraint qualification Mathematics Subject Classification (1991): 90C30, 90C31, 90C34, 49M39
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    Notes: Abstract. The paper deals with semi-infinite optimization problems which are defined by finitely many equality constraints and infinitely many inequality constraints. We generalize the concept of strongly stable stationary points which was introduced by Kojima for finite problems; it refers to the local existence and uniqueness of a stationary point for each sufficiently small perturbed problem, where perturbations up to second order are allowed. Under the extended Mangasarian-Fromovitz constraint qualification we present equivalent conditions for the strong stability of a considered stationary point in terms of first and second derivatives of the involved functions. In particular, we discuss the case where the reduction approach is not satisfied.
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    Mathematical programming 86 (1999), S. 313-334 
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    Keywords: Key words: linear programming – potential functions – infeasible-interior-point methods – homogeneity – self-dual
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  • 73
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    Keywords: Key words: basis recovery – partition – principal pivot transforms – Balinski-Tucker tableaus – quadratic programming – linear complementarity problems – interior point methods – sufficient matrices – crossover – Criss-Cross method
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    Notes: Abstract. Optimal solutions of interior point algorithms for linear and quadratic programming and linear complementarity problems provide maximally complementary solutions. Maximally complementary solutions can be characterized by optimal partitions. On the other hand, the solutions provided by simplex–based pivot algorithms are given in terms of complementary bases. A basis identification algorithm is an algorithm which generates a complementary basis, starting from any complementary solution. A partition identification algorithm is an algorithm which generates a maximally complementary solution (and its corresponding partition), starting from any complementary solution. In linear programming such algorithms were respectively proposed by Megiddo in 1991 and Balinski and Tucker in 1969. In this paper we will present identification algorithms for quadratic programming and linear complementarity problems with sufficient matrices. The presented algorithms are based on the principal pivot transform and the orthogonality property of basis tableaus.
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    Mathematical programming 86 (1999), S. 417-431 
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    Keywords: Mathematics Subject Classification (1991): 90A11, 90B50, 90C90, 90D65
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    Notes: Abstract. We study the following decision-making scenario: A linear program is solved by a set of agents arranged hierarchically in a tree, where each agent decides the level of certain variables, and has a distinct objective function, known to all agents. Authority is reflected in two ways: Agents higher in the tree set their variables first; and agents that are siblings in the tree resolve their game by focusing on the Nash equilibrium that is optimum for the agent above them. We give a necessary and sufficient condition for such a hierarchy to be efficient (i.e., to have perfect coordination, to ultimately optimize the objective of the firm). We study problems related to designing a hierarchy (assigning decision makers to positions in the tree) in order to achieve efficiency or otherwise optimize coordination.
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    Mathematical programming 86 (1999), S. 533-563 
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    Keywords: Key words: generalized linear complementarity problem – non-interior continuation method – Newton method – Q-quadratical convergence Mathematics Subject Classification (1991): 90C33
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    Notes: Abstract. In this paper, we propose a non-interior continuation method for solving generalized linear complementarity problems (GLCP) introduced by Cottle and Dantzig. The method is based on a smoothing function derived from the exponential penalty function first introduced by Kort and Bertsekas for constrained minimization. This smoothing function can also be viewed as a natural extension of Chen-Mangasarian’s neural network smooth function. By using the smoothing function, we approximate GLCP as a family of parameterized smooth equations. An algorithm is presented to follow the smoothing path. Under suitable assumptions, it is shown that the algorithm is globally convergent and local Q-quadratically convergent. Few preliminary numerical results are also reported.
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    Mathematical programming 86 (1999), S. 463-473 
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    Keywords: Key words: semidefinite relaxations – quadratic programming Mathematics Subject Classification (1991): 20E28, 20G40, 20C20
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    Notes: Abstract. We demonstrate that if A 1,...,A m are symmetric positive semidefinite n×n matrices with positive definite sum and A is an arbitrary symmetric n×n matrix, then the relative accuracy, in terms of the optimal value, of the semidefinite relaxation $$\max_X\{\Tr(AX)\mid\, \Tr(A_iX)\le1,\,\,i=1,...,m;\,X\succeq0\} \eqno{\hbox{(SDP)}}$$ of the optimization program $$x^TAx\to\max\mid\, x^TA_ix\le 1,\,\,i=1,...,m \eqno{\hbox{(P)}}$$ is not worse than $$1-\frac{1}{{2\ln(2m^2)}}$$ . It is shown that this bound is sharp in order, as far as the dependence on m is concerned, and that a~feasible solution x to (P) with $$x^TAx\ge \frac{{\Opt(\hbox{{\rm SDP}})}}{{2\ln(2m^2)}} \eqno{(*)}$$ can be found efficiently. This somehow improves one of the results of Nesterov [4] where bound similar to (*) is established for the case when all Ai are of rank 1.
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    Mathematical programming 86 (1999), S. 161-185 
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    Keywords: Mathematics Subject Classification (1991): 90C10
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    Notes: Abstract. This paper considers the precedence constrained knapsack problem. More specifically, we are interested in classes of valid inequalities which are facet-defining for the precedence constrained knapsack polytope. We study the complexity of obtaining these facets using the standard sequential lifting procedure. Applying this procedure requires solving a combinatorial problem. For valid inequalities arising from minimal induced covers, we identify a class of lifting coefficients for which this problem can be solved in polynomial time, by using a supermodular function, and for which the values of the lifting coefficients have a combinatorial interpretation. For the remaining lifting coefficients it is shown that this optimization problem is strongly NP-hard. The same lifting procedure can be applied to (1,k)-configurations, although in this case, the same combinatorial interpretation no longer applies. We also consider K-covers, to which the same procedure need not apply in general. We show that facets of the polytope can still be generated using a similar lifting technique. For tree knapsack problems, we observe that all lifting coefficients can be obtained in polynomial time. Computational experiments indicate that these facets significantly strengthen the LP-relaxation.
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    Mathematical programming 34 (1986), S. 1-33 
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    Keywords: Polyhedra ; Chinese Postman ; Binary Group Problems ; Binary Matroids ; Blocking Clutters
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    Notes: Abstract A new proof of the characterization of the Chinese postman polyhedra is given. In developing this proof, a theorem of Gomory about homomorphic lifting of facets for group polyhedra is generalized to subproblems. Some results for the Chinese postman problem are generalized to binary group problems. In addition, a connection is made between Fulkerson's blocking polyhedra and a blocking pair of binary group problems. A connection is also developed between minors and lifting of facets for group problems.
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    Mathematical programming 34 (1986), S. 48-61 
    ISSN: 1436-4646
    Keywords: Total Dual Integrality ; Hilbert Basis ; Polyhedra
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    Notes: Abstract Edmonds and Giles introduced the class of box totally dual integral polyhedra as a generalization of submodular flow polyhedra. In this paper a geometric characterization of these polyhedra is given. This geometric result is used to show that each TDI defining system for a box TDI polyhedron is in fact a box TDI system, that the class of box TDI polyhedra is in co-NP and is closed under taking projections and dominants, that the class of box perfect graphs is in co-NP, and a result of Edmonds and Giles which is related to the facets of box TDI polyhdera.
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    Mathematical programming 34 (1986), S. 72-83 
    ISSN: 1436-4646
    Keywords: Cutting Planes ; Disjunctive Programming
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    Notes: Abstract The duality between facets of the convex hull of disjunctive sets and the extreme points of reverse polars of these sets is utilized to establish simple rules for the derivation of all facet cuts for simple disjunctions, namely, elementary disjunctions in nonnegative variables. These rules generalize the cut generation procedure underlying polyhedral convexity cuts with negative edge extensions. The latter are also shown to possess some interesting properties with respect to a biextremal problem that maximizes the distance, from the origin, of the nearest point feasible to the cut. A computationally inexpensive procedure is given to generate facet cuts for simple disjunctions which are dominant with respect to any specified preemptive ordering of variables.
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    Mathematical programming 34 (1986), S. 111-124 
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    Keywords: Global Optimization ; Stochastic Optimization ; Annealing ; Metropolis Method ; NP ; Hill Climbing ; Local Improvement
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    Notes: Abstract The annealing algorithm is a stochastic optimization method which has attracted attention because of its success with certain difficult problems, including NP-hard combinatorial problems such as the travelling salesman, Steiner trees and others. There is an appealing physical analogy for its operation, but a more formal model seems desirable. In this paper we present such a model and prove that the algorithm converges with probability arbitrarily close to 1. We also show that there are cases where convergence takes exponentially long—that is, it is no better than a deterministic method. We study how the convergence rate is affected by the form of the problem. Finally we describe a version of the algorithm that terminates in polynomial time and allows a good deal of ‘practical’ confidence in the solution.
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    Mathematical programming 34 (1986), S. 125-141 
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    Keywords: Assignment Problem ; Dual Method ; Signature ; Linear Programming ; Simplex Method ; Pivoting ; Average Behavior
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    Notes: Abstract “Where there is abundance of mystery and confusion in every direction, the truth seldom remains hidden for long. It's a matter of having plenty of angles to go at it from. Only the utterly simple crimes - the simplex crimes, you may say - have the trick of remaining baffling.” - Sir John (from Michael Innes,The Open House (A Sir John Appleby Mystery), Penguin Books, 1974). A dual simplex method for the assignment problem leaves open to choice the activity (i,j) of rowi and columnj that is to be dropped in pivoting so long asx ij 〈 0. A choice (i,j) over columnsj having at least 3 basic activities that minimizesx ij is shown to converge in at most ( 2 n-1 ) pivots, and at most O(n 3) time, and it is argued that on average the number of pivots is at mostn logn.
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    Mathematical programming 34 (1986), S. 142-162 
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    Keywords: Network Design ; Bilevel Programming ; Variational Inequalities ; Stackelberg Games
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    Notes: Abstract Recently much attention has been focused on multilevel programming, a branch of mathematical programming that can be viewed either as a generalization of min-max problems or as a particular class of Stackelberg games with continuous variables. The network design problem with continuous decision variables representing link capacities can be cast into such a framework. We first give a formal description of the problem and then develop various suboptimal procedures to solve it. Worst-case behaviour results concerning the heuristics, as well as numerical results on a small network, are presented.
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    Mathematical programming 34 (1986), S. 175-187 
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    Keywords: Primary 65K05 ; Secondary 90C25 ; Nonsmooth Optimization ; Nondifferentiable Programming ; Linearly Constrained Minimization ; Descent Methods
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    Notes: Abstract A readily implementable algorithm is given for minimizing a (possibly nondifferentiable and nonconvex) locally Lipschitz continuous functionf subject to linear constraints. At each iteration a polyhedral approximation tof is constructed from a few previously computed subgradients and an aggregate subgradient, which accumulates the past subgradient information. This aproximation and the linear constraints generate constraints in the search direction finding subproblem that is a quadratic programming problem. Then a stepsize is found by an approximate line search. All the algorithm's accumulation points are stationary. Moreover, the algorithm converges whenf happens to be convex.
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    Mathematical programming 34 (1986), S. 248-249 
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    Mathematical programming 34 (1986), S. 251-264 
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    Keywords: Integer Linear Programming ; Chvátal Rank ; Cutting Planes ; Sensitivity Analysis
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    Notes: Abstract We consider integer linear programming problems with a fixed coefficient matrix and varying objective function and right-hand-side vector. Among our results, we show that, for any optimal solution to a linear program max{wx: Ax≤b}, the distance to the nearest optimal solution to the corresponding integer program is at most the dimension of the problem multiplied by the largest subdeterminant of the integral matrixA. Using this, we strengthen several integer programming ‘proximity’ results of Blair and Jeroslow; Graver; and Wolsey. We also show that the Chvátal rank of a polyhedron {x: Ax≤b} can be bounded above by a function of the matrixA, independent of the vectorb, a result which, as Blair observed, is equivalent to Blair and Jeroslow's theorem that ‘each integer programming value function is a Gomory function.’
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    Mathematical programming 34 (1986), S. 302-332 
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    Keywords: Generalized Programming ; Competitive Equilibria ; Economic Modelling
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    Notes: Abstract We present a modification of the Manne-Chao-Wilson algorithm for computing competitive equilibria and discuss some of its convergence properties. Numerical experiments involving models with up to 100 price responsive agents are provided.
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    Mathematical programming 34 (1986), S. 292-301 
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    Keywords: Selection Rules ; Linear Programming ; Linear Complementarity ; Network Flows
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    Notes: Abstract Affirmative action is a new variety of selection rule which employs historical information to favor the choice of elements that have not been selected in the past. We categorize three implementations of this principle and discuss their application to the simplex method, to Bard-type schemes for the linear complementarity problem, and to augmenting path methods for network flow problems. We present analytical and computational results, and some open questions.
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    Mathematical programming 34 (1986), S. 265-291 
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    Keywords: Linear Complementarity Problems ; Complementary Cones ; Invariant Number of Solutions
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    Notes: Abstract This paper studies the class INS of all realn × n matricesM for which the linear complementarity problem (q, M) has exactlyk solutions—k depending only onM—for all realn-vectorsq interior to the coneK(M) of vectors for which (q, M) has any solution at all. This generalizes the results in Cottle and Stone (1983) which deal with the subclassU in INS wherek equals one. After the first two sections of this paper, which introduce the problem and background material, we move on to examine necessary conditions for a matrixM to be in INS (Section 3) and sufficient conditions under whichM will be in INS (Section 4). Section 5 deals with the possible values whichk may have. Section 6 discusses related results concerning the geometry of linear complementarity problems. Finally, Section 7 deals with some known and new matrix classes which are in INS.
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    Mathematical programming 34 (1986), S. 370-371 
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    Mathematical programming 34 (1986), S. 372-372 
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    Mathematical programming 70 (1995), S. 27-45 
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    Keywords: Convex polytopes ; Enumeration of faces ; Adjacency ; Segments
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    Notes: Abstract We introduce the concept of a segment of a degenerate convex polytope specified by a system of linear constraints, and explain its importance in developing algorithms for enumerating the faces. Using segments, we describe an algorithm that enumerates all the faces, in time polynomial in their number. The role of segments in the unsolved problem of enumerating the extreme points of a convex polytope specified by a degenerate system of linear constraints, in time polynomial in the number of extreme points, is discussed.
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    Mathematical programming 70 (1995), S. 47-72 
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    Keywords: Bilevel programming ; Nonlinear nonconvex ; Nondifferentiable optimization ; Economic planning ; Sensitivity analysis
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    Notes: Abstract This paper is concerned with general nonlinear nonconvex bilevel programming problems (BLPP). We derive necessary and sufficient conditions at a local solution and investigate the stability and sensitivity analysis at a local solution in the BLPP. We then explore an approach in which a bundle method is used in the upper-level problem with subgradient information from the lower-level problem. Two algorithms are proposed to solve the general nonlinear BLPP and are shown to converge to regular points of the BLPP under appropriate conditions. The theoretical analysis conducted in this paper seems to indicate that a sensitivity-based approach is rather promising for solving general nonlinear BLPP.
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    Mathematical programming 70 (1995), S. 123-148 
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    Keywords: Generalized equations ; Variational inequalities ; Nonlinear programming ; Sensitivity analysis ; Power series ; Strong regularity ; Constrained optimization ; Perturbation theory
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    Notes: Abstract We show that the solution of a strongly regular generalized equation subject to a scalar perturbation expands in pseudopower series in terms of the perturbation parameter, i.e., the expansion of orderk is the solution of generalized equations expanded to orderk and thus depends itself on the perturbation parameter. In the polyhedral case, this expansion reduces to a usual Taylor expansion. These results are applied to the problem of regular perturbation in constrained optimization. We show that, if the strong regularity condition is satisfied, the property of quadratic growth holds and, at least locally, the solutions of the optimization problem and of the associated optimality system coincide. If, in addition the number of inequality constraints is finite, the solution and the Lagrange multiplier can be expanded in Taylor series. If the data are analytic, the solution and the multiplier are analytic functions of the perturbation parameter.
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    Mathematical programming 70 (1995), S. 201-209 
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    Keywords: Disjoint paths ; Joins ; Packing cuts
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    Notes: Abstract Seymour (1981) proved that the cut criterion is necessary and sufficient for the solvability of the edge-disjoint paths problem when the union of the supply graph and the demand graph is planar and Eulerian. When only planarity is required, Middendorf and Pfeiffer (1993) proved the problem to be NP-complete. For this case, Korach and Penn (1992) proved that the cut criterion is sufficient for the existence of a near-complete packing of paths. Here we generalize this result by showing how a natural strengthening of the cut criterion yields better packings of paths. Analogously to Seymour's approach, we actually prove a theorem on packing cuts in an arbitrary graph and then the planar edge-disjoint paths case is obtained by planar dualization. The main result is derived from a theorem of Sebő (1990) on the structure of ±1 weightings of a bipartite graph with no negative circuits.
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    Mathematical programming 70 (1995), S. 279-351 
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    Keywords: Linear programming ; Complexity theory ; Interior-point methods ; Semi-definite programming ; Condition numbers ; Convex programming
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    Notes: Abstract We propose analyzing interior-point methods using notions of problem-instance size which are direct generalizations of the condition number of a matrix. The notions pertain to linear programming quite generally; the underlying vector spaces are not required to be finite-dimensional and, more importantly, the cones defining nonnegativity are not required to be polyhedral. Thus, for example, the notions are appropriate in the context of semi-definite programming. We prove various theorems to demonstrate how the notions can be used in analyzing interior-point methods. These theorems assume little more than that the interiors of the cones (defining nonnegativity) are the domains of self-concordant barrier functions.
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    Mathematical programming 71 (1995), S. 17-28 
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    Keywords: Descent method ; Proximal algorithm ; Direction-finding subproblem
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    Notes: Abstract Most of the descent methods developed so far suffer from the computational burden due to a sequence of constrained quadratic subproblems which are needed to obtain a descent direction. In this paper we present a class of proximal-type descent methods with a new direction-finding subproblem. Especially, two of them have a linear programming subproblem instead of a quadratic subproblem. Computational experience of these two methods has been performed on two well-known test problems. The results show that these methods are another very promising approach for nondifferentiable convex optimization.
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    Mathematical programming 71 (1995), S. 51-69 
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    Keywords: Smoothing ; Convex inequalities ; Linear complementarity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract A smooth approximationp (x, α) to the plus function max{x, 0} is obtained by integrating the sigmoid function 1/(1 + e−αx ), commonly used in neural networks. By means of this approximation, linear and convex inequalities are converted into smooth, convex unconstrained minimization problems, the solution of which approximates the solution of the original problem to a high degree of accuracy forα sufficiently large. In the special case when a Slater constraint qualification is satisfied, an exact solution can be obtained for finiteα. Speedup over MINOS 5.4 was as high as 1142 times for linear inequalities of size 2000 × 1000, and 580 times for convex inequalities with 400 variables. Linear complementarity problems are converted into a system of smooth nonlinear equations and are solved by a quadratically convergent Newton method. For monotone LCPs with as many as 10 000 variables, the proposed approach was as much as 63 times faster than Lemke's method.
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  • 99
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 71 (1995), S. 127-136 
    ISSN: 1436-4646
    Keywords: Parametric optimization ; Mixed-integer program ; Value functions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract We identify a class of formulas computable in polynomial time such that the functions defined by these formulas are precisely the value functions of mixed-integer programs with rational constraint coefficients.
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  • 100
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 71 (1995), S. 137-151 
    ISSN: 1436-4646
    Keywords: Quadratic assignment problem ; Lower bounds
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract We consider transformations of the (metric) Quadratic Assignment Problem (QAP) that exploit the metric structure of a given instance. We show in particular how the structural properties of rectangular grids can be used to improve a given lower bound. Our work is motivated by previous research of Palubetskes (1988), and it extends a bounding approach proposed by Chakrapani and Skorin-Kapov (1993). Our computational results indicate that the present approach is practical; it has been applied to problems of dimension up ton = 150. Moreover, the new approach yields by far the best lower bounds on most of the instances of metric QAPs that we considered.
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