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  • Articles  (2,834)
  • Springer  (2,834)
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  • 1995-1999  (2,834)
  • 1995  (2,834)
  • Computer Science  (2,834)
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  • Articles  (2,834)
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  • 1995-1999  (2,834)
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  • 1
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    Springer
    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
    Topics: Computer Science , Mathematics
    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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  • 2
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    Mathematical programming 69 (1995), S. 1-43 
    ISSN: 1436-4646
    Keywords: Mathematical programming ; Cutting planes ; Analytic center
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    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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  • 3
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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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    Topics: Computer Science , Mathematics
    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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  • 4
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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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  • 5
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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
    Topics: Computer Science , Mathematics
    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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  • 6
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    Mathematical programming 69 (1995), S. 335-349 
    ISSN: 1436-4646
    Keywords: Polyhedral combinatorics ; Valid inequalities ; Travelling salesman ; Worst-case analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    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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  • 7
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    Mathematical programming 70 (1995), S. 1-16 
    ISSN: 1436-4646
    Keywords: Stochastic programming ; Polyhedral functions ; Simplicial functions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    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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  • 8
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    Mathematical programming 70 (1995), S. 107-122 
    ISSN: 1436-4646
    Keywords: Linear complementarity problem ; Predictor—corrector algorithm ; Complexity analysis ; Central trajectory ; Curvature integral ; Interior-point methods
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    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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  • 9
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    Mathematical programming 70 (1995), S. 159-172 
    ISSN: 1436-4646
    Keywords: Parametric nonlinear programming ; Directional differentiability ; B-derivative ; Piecewise smooth function ; Nonunique multipliers ; Degeneracy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    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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  • 10
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    Mathematical programming 70 (1995), S. 191-200 
    ISSN: 1436-4646
    Keywords: Strictly pseudomonotone map ; Z-map ; Complementarity problem ; Least element problem
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    Topics: Computer Science , Mathematics
    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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  • 11
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    Mathematical programming 70 (1995), S. 251-277 
    ISSN: 1436-4646
    Keywords: Linear programming ; Barrier methods ; Interior-point methods
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    Topics: Computer Science , Mathematics
    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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  • 12
    ISSN: 1436-4646
    Keywords: Linear programming ; Mixed-integer programming ; Large-scale optimization ; Airline fleet assignment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    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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  • 13
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    Mathematical programming 71 (1995), S. 77-100 
    ISSN: 1436-4646
    Keywords: Convex linearly constrained problems ; Variational inequalities ; Interior methods ; Entropy-like proximal method ; Maximal monotone operator
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    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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  • 14
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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
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    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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  • 15
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    Mathematical programming 71 (1995), S. 101-112 
    ISSN: 1436-4646
    Keywords: Minmax ; Maximal covering problems ; Multi criteria decision-making
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    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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  • 16
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    Mathematical programming 71 (1995), S. 71-76 
    ISSN: 1436-4646
    Keywords: Location theory ; Fermat—Weber problem ; Weiszfeld's iterative algorithm
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    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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  • 17
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    Mathematical programming 71 (1995), S. 153-177 
    ISSN: 1436-4646
    Keywords: Network optimization ; Assignment problem ; Algorithms ; Experimental evaluation ; Cost scaling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    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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  • 18
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    Mathematical programming 71 (1995), S. 195-206 
    ISSN: 1436-4646
    Keywords: Superfluous matrix ; Linear complementarity problem
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    Topics: Computer Science , Mathematics
    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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  • 19
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    Mathematical programming 71 (1995), S. 249-258 
    ISSN: 1436-4646
    Keywords: Combinatorial optimization ; Integrality of polyhedra ; Generalized set packing ; Covering
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    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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  • 20
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    Mathematical programming 71 (1995), S. 369-370 
    ISSN: 1436-4646
    Keywords: Local Lipschitz property ; Infinite-dimensional Hilbert space
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    Topics: Computer Science , Mathematics
    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 70 (1995), S. 27-45 
    ISSN: 1436-4646
    Keywords: Convex polytopes ; Enumeration of faces ; Adjacency ; Segments
    Source: Springer Online Journal Archives 1860-2000
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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 
    ISSN: 1436-4646
    Keywords: Bilevel programming ; Nonlinear nonconvex ; Nondifferentiable optimization ; Economic planning ; Sensitivity analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    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 
    ISSN: 1436-4646
    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 
    ISSN: 1436-4646
    Keywords: Disjoint paths ; Joins ; Packing cuts
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    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 
    ISSN: 1436-4646
    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 
    ISSN: 1436-4646
    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 
    ISSN: 1436-4646
    Keywords: Smoothing ; Convex inequalities ; Linear complementarity
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    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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    Mathematical programming 71 (1995), S. 127-136 
    ISSN: 1436-4646
    Keywords: Parametric optimization ; Mixed-integer program ; Value functions
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    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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    Mathematical programming 71 (1995), S. 137-151 
    ISSN: 1436-4646
    Keywords: Quadratic assignment problem ; Lower bounds
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    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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    Mathematical programming 71 (1995), S. 207-219 
    ISSN: 1436-4646
    Keywords: Subgradient optimization ; Relaxation methods ; Projection methods
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    Notes: Abstract We study conditions for convergence of a generalized subgradient algorithm in which a relaxation step is taken in a direction, which is a convex combination of possibly all previously generated subgradients. A simple condition for convergence is given and conditions that guarantee a linear convergence rate are also presented. We show that choosing the steplength parameter and convex combination of subgradients in a certain sense optimally is equivalent to solving a minimum norm quadratic programming problem. It is also shown that if the direction is restricted to be a convex combination of the current subgradient and the previous direction, then an optimal choice of stepsize and direction is equivalent to the Camerini—Fratta—Maffioli modification of the subgradient method.
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    Mathematical programming 71 (1995), S. 221-245 
    ISSN: 1436-4646
    Keywords: Linear programming ; Presolving ; Interior-point methods
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    Notes: Abstract Most modern linear programming solvers analyze the LP problem before submitting it to optimization. Some examples are the solvers WHIZARD (Tomlin and Welch, 1983), OB1 (Lustig et al., 1994), OSL (Forrest and Tomlin, 1992), Sciconic (1990) and CPLEX (Bixby, 1994). The purpose of the presolve phase is to reduce the problem size and to discover whether the problem is unbounded or infeasible. In this paper we present a comprehensive survey of presolve methods. Moreover, we discuss the restoration procedure in detail, i.e., the procedure that undoes the presolve. Computational results on the NETLIB problems (Gay, 1985) are reported to illustrate the efficiency of the presolve methods.
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    Computing 54 (1995), S. 303-316 
    ISSN: 1436-5057
    Keywords: 05 C 60 ; 05 C 85 ; Graph isomorphism ; automorphism partition ; polynomial algorithm ; chordal graphs ; graphs with fewP 4s
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Ein Graph ist chordal, wenn er keine sehnenlosen Kreise der Länge mindestens vier enthält und (q, t), wenn keine Menge von höchstensq Knoten mehr alst Wege der Länge drei induziert. Es ist bekannt, daß das Isomorphieproblem für chordale Graphen und für (6, 3) Graphen Isomorphie-vollständig ist. Wir stellen polynomiale Verfahren vor zur Bestimmung der Automorphiepartition und zum Testen der Isomorphie von Graphen, die sowohl chrodal als auch (6, 3) sind. Der zugang basiert auf dem Studium von simplizialen Partitionen von chordalen Graphen. Es wird gezeigt, daß für chordale (6, 3) Graphen die Automorphiepartition mit der gröbsten regulären simplizialen Partition übereinstimmt. Dies führt zu einemO(n+m logn) isomorphietest.
    Notes: Abstract A graph is chordal if it contains no chordless cycles of length at least four and (q, t) if no set of at mostq vertices induces more thant paths of length three. It is known that the isomorphism problem is isomorphism complete for chordal graphs and for (6, 3) graphs. We present polynomial methods to determine the automorphism partition and to test isomorphism of graphs which are both chordal and (6, 3). The approach is based on the study of simplicial partitions of chordal graphs. It is proved that for chordal (6, 3) graphs the automorphism partition coincides with the coarsest regular simplicial partition. This yields anO(n+m logn) isomorphism test.
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    Computing 54 (1995), S. 317-330 
    ISSN: 1436-5057
    Keywords: 65M06 ; 65M55 ; 65Y05 ; Parabolic partial differential equation ; Multigird ; parallel computing
    Source: Springer Online Journal Archives 1860-2000
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    Description / Table of Contents: Zusammenfassung Die Erscheinung von Parallelrechnern hat zur Entwicklung neuer Lösungsverfahren for zeitabhängige partielle Differentialgleichungen geführt. Zwei der in letzter Zeit entwickelten Verfahren — die Mehrgitter-Wellenformrelaxations-Methode und die zeitparallele Mehrgittermethode —haben zum Ziel, die Lösung zu vielen verschiedenen diskreten Zeitpunkten simultan zu berechnen. In dieser Arbeit wird anhand der Ergebnisse einer Fourier-Analyse für ein Modell-problem das Konvergenzverhalten beider Methoden verglichen.
    Notes: Abstract The advent of parallel computers has led to the development of new solution algorithms for time-dependent partial differential equations. Two recently developed methods, multigrid waveform relaxation and time-parallel multigrid, have been designed to solve parabolic partial differential equations on many time-levels simultaneously. This paper compares the convergence properties of these methods, based on the results of an exponential Fourier mode analysis for a model problem.
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  • 34
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    Computing 54 (1995), S. 251-272 
    ISSN: 1436-5057
    Keywords: Iterative process ; variational inequality ; non-accurate iteration ; projection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Diese Arbeit behandelt numerische Methoden zur Lösung linearer Variations-Ungleichungen auf einer abgeschlossenen konvexen Teilmenge des ℝn. Es gibt zwar zahlreiche Iterationsverfahren für den FallC=ℝ + n für den Fall einer beliebigen abgeschlossenen konvexen TeilmengeC wurde aber nur wenig vorgeschlagen. Die wesentliche Schwierigkeit in diesem Fall liegt in den Nichtlinearitäten des Randes vonC. In dieser Arbeit werden Iterationsverfahren zur Lösung linearer Variations-Ungleichungen auf einer beliebigen abgeschlossenen konvexen TeilmengeC entwickelt. In unseren Algorithmen wird die Berechnung einer linearen Variations-Ungleichung zerlegt in eine Folge von Projektionen eines Vektors auf die abgeschlossene konvexe TeilmengeC, die berechnet werden können, solange die Bestimmungsgleichungen des Randes gegeben sind. Insbesondere kann mit unseren Iterationsverfahren leicht eine Lösung berechnet werden fürC als Würfel, Kugel, Ellipsoid etc. Außerdem werden Näherungs-Iterationen, Abschätzung der Lösungen für unbeschränkte Bereiche und die Theorie der Randapproximation untersucht. Weiters wird eine notwendige und hinreichende Bedingung dafür angegeben, daß ein Vektor eine Näherungslösung ist. Schließlich werden einige numerische Beispiele präsentiert, die zeigen, daß die vorgestellten Algorithmen effektiv und effizient sind.
    Notes: Abstract This paper deals with numerical methods for solving linear variational inequalities on an arbitrary closed convex subsetC of ℝ n . Although there were numerous iterations studied for the caseC=ℝ + n , few were proposed for the case whenC is a closed convex subset. The essential difficulty in this case is the nonlinearities ofC's boundaries. In this paper iteration processes are designed for solving linear variational inequalities on an arbitrary closed convex subsetC. In our algorithms the computation of a linear variational inequality is decomposed into a sequence of problems of projecting a vector to the closed convex subsetC, which are computable as long as the equations describing the boundaries are given. In particular, using our iterations one can easily compute a solution whenC is one of the common closed convex subsets such as cube, ball, ellipsoid, etc. The non-accurate iteration, the estimate of the solutions on unbounded domains and the theory of approximating the boundaries are also established. Moreover, a necessary and sufficient condition is given for a vector to be an approximate solution. Finally, some numerical examples are presented, which show that the designed algorithms are effective and efficient. The exposition of this paper is self-contained.
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    Computing 54 (1995), S. 331-346 
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    Keywords: 65N55 ; 65N30 ; Frequency decomposition ; multi-level method ; finite elements ; hierarchical basis ; additive and multiplicative Schwarz methods ; subspace decomposition ; robustness
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Kürzlich haben wir eine effektive Modifizierung des Frequenzzerlegungs-Mehrgitterverfahrens vorgestellt. In diesem Artikel wird die multiplikative Variante dieses Verfahrens untersucht. Unter Verwendung der Theorie der Unterraumkorrekturverfahren wird die Robustheit sowohl für die multiplikative als auch für die additive Variante bei Anwendung auf anisotrope Probleme mit beliebiger Raumdimension bewiesen. Die Implementierung beider Varianten wird diskutiert und numerische Ergebnisse werden angegeben.
    Notes: Abstract Recently, we introduced a cheap modification of Hackbusch'sFrequency Decomposition multi-level method. In this paper, the multiplicative variant of this method is studied. Using the theory of Subspace Correction Methods robustness is proved of both the multiplicative and additive variant applied to anisotropic problems in an arbitrary number of space dimensions. Implementation of both variants is discussed and numerical results are given.
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  • 36
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    Computing 54 (1995), S. 347-357 
    ISSN: 1436-5057
    Keywords: 65G10 ; 65L05 ; 65L07 ; Interval arithmetic ; interval methods for the initial value problem
    Source: Springer Online Journal Archives 1860-2000
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    Description / Table of Contents: Zusammenfassung Wenn Systeme gewöhnlicher Differentialgleichungen mit Intervallmethoden gelöst werden, besteht die Hauptschwierigkeit in der Reduktion des Wrappingeffekts. Die verschiedenen bis jetzt vorgeschlagenen Lösungen sind nur bei engen Anfangsintervallen oder speziellen Gleichungsklassen anwendbar. Diese Arbeit beschreibt einen Algorithmus, der statt Intervallen eine größere Familie von Mengen verwendet. Der Algorithmus führt zu einem sehr geringen Wrappingeffekt und ist bei beliebigem Gleichungstyp und weiten Anfangsintervallen anwendbar. Zum gegenwärtigen Zeitpunkt können nur 2-dimensionale Probleme behandelt werden.
    Notes: Abstract When solving ODEs by interval methods, the main difficulty is reducing the wrapping effect. Various solutions have been put forward, all of which are applicable for narrow initial intervals or to particular classes of equations only. This paper describes an algorithm which, instead of intervals, uses a larger family of sets. The algorithm exhibits a very small wrapping effect and applies to any type of equation and initial region. For the time being it handles only two-dimensional equations.
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    Computing 54 (1995), S. 359-375 
    ISSN: 1436-5057
    Keywords: AMS(MOS) ; 65H05 ; Polynomial zeros ; Eulidean division of Chebyshev expansions ; Sturm sequences
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Wir stellen einen global konvergenten Algorithmus zur Berechnung aller Nullstellen eines Polynomsp n ,p n (z) = ∑ v = 0 n a v z v, mit reellen Koeffizienten vor. Durch Aufspalten vonp n (exp(it)) in seinen Real-und Imaginärteil können wir mittels Euklidischer Division von Čebyševentwicklungen und durch Argumentation mit Sturmschen Ketten entscheiden, obp n Nullstellen im Einheitskreis hat und wie viele Nullstellen auf dem Rand und im Inneren davon liegen. Somit erhalten wir mittels einer Bisektionsstrategie die Beträge aller Nullstellen bis auf eine vorgegebene Genauigkeit, und zusätzlich finden wir die Argumente als reelle Nullstellen eines Polynoms niedrigen Grades. Auf diese Weise erzeugen wir Startnäherungen für alle Nullstellen, die in einem letzten Schritt mittels eines iterativen Prozesses höherer Konvergenzordnung verbessert werden (z.B. Newton- oder Bairstowverfahren).
    Notes: Abstract We present a globally convergent algorithm for calculating all zeros of a polynomialp n ,p n (z) = ∑ v = 0 n a v z v, with real coefficients. Splittingp n (exp(it)) into its real and imaginary part we can decide via Euclidean division of Chebyshev expansions and Sturm sequence argumentations whetherp n has some zeros on the unit circle and how many zeros lie on the boundary and in the interior of it. Hence, by a bisection strategy we get the moduli of all zeros to a prescribed accuracy, and additionally we find the arguments as real zeros of a low degree polynomial. In this way we generate starting approximations for all zeros which in a final step are refined by an iterative process of higher order of convergence (e.g. Newton's or Bairstow's method).
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    Computing 55 (1995), S. 23-42 
    ISSN: 1436-5057
    Keywords: Radiosity ; Monte Carlo ; algorithms ; stochastic convergence ; transillumination method ; stochastic shooting method ; variance reduction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Die vorgestellten neuen Radiosity Methoden für diffuse Szenen sind besonders geeignet, um die Lichtausbreitung in sehr komplexen Umgebungen in linearer Zeit zu berechnen. Die Verfahren beruhen auf rekursiven Algorithmen, die das Radiosity-Gleichungssystem mittels stochastischer Konvergenz löseu. Approximationen der ‘gathering-’ und ‘shooting-’ Verfahren werden statt einer exakten Berechnung jedes Reflexionsschrittes verwendet. Die Effizienz der Verfahren kann durch geeignete Varianzreduktionsmethoden verbessert werden.
    Notes: Abstract The fast radiosity-type methods for very complex diffuse environments, introduced herein, present a nearly linear-time solution. The outlined procedures rely on recursive algorithms with stochastic convergence for solving the radiosity equation system. Approximations of gathering and shooting at very low computational cost—rather than the exact matrix of a single reflection—are used. The efficiency of the methods will be increased by applying variance reduction techniques.
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    Computing 55 (1995), S. 43-53 
    ISSN: 1436-5057
    Keywords: Interval analysis ; range computation ; inclusion monotonicity ; Bernstein coefficients
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    Description / Table of Contents: Zusammenfassung Bekanntlich ist der Wertebereich eines Polynomsf über einem Intervall durch den kleinsten und größten Koeffizienten vonf bezüglich der Bernstein Basis auf dem Intervall eingeschränkt. Dadurch wird eine IntervallerweiterungF vonf definiert, die sogenannte Bernstein Form. In dieser Arbeit zeigen wir, daß die Bernstein Form inklusionsmonoton ist, d. h. wenn.X⊇Y dannF(X)⊇F(Y).
    Notes: Abstract It is well known that the range of polynomialf over an interval is bounded by the smallest and the largest coefficient off with respect to the Bernstein basis over the interval. This defines an interval extensionF off, which is called Bernstein form. In this paper we show that the bernstein form is inclusion monotone, i.e.X⊇Y impliesF(X)⊇F(Y).
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    Computing 55 (1995), S. 1-22 
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    Keywords: 65L ; 34C ; Reversible integration ; symplectic integrators ; variable step size ; long time integration
    Source: Springer Online Journal Archives 1860-2000
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    Description / Table of Contents: Zusammenfassung Werden symplektische oder reversible Integrationsverfahren mit herkömmlichen Schrittweitensteuerungen verwendet, so geht die symplektische, bzw. die reversible Struktur des Problems verloren. In dieser Arbeit wird gezeigt, dass die symplektische Struktur des Verfahrens nur dann erhalten wird, wenn die Schrittweite fast konstant bleibt. Für reversible Verfahren sind echt variable Schrittweiten möglich, die Schrittweite muss jedoch für “gespiegelte” Schritte gleich sein. Es werden verschiedene Wege aufgezeigt, um reversible, variable Schrittweiten zu konstruieren. Numerische Experimente zeigen, dass für das Keplerproblem die neuen Methoden den herkömmlichen Schrittweitensteuerungen oder den symplektischen Verfahren mit konstanter Schrittweite überlegen sind. Insbesondere wächst der globale Fehler linear.
    Notes: Abstract Conventional variable-step implementation of symplectic or reversible integration methods destroy the symplectic or reversible structure of the system. We show that to preserve the symplectic structure of a method the step size has to be kept almost constant. For reversible methods variable steps are possible but the step size has to be equal for “reflected” steps. We demonstrate possible ways to construct reversible variable step size methods. Numerical experiments show that for the Kepler problem the new methods perform better than conventional variable step size methods or symplectic constant step size methods. In particular they exhibit linear growth of the global error (as symplectic methods with constant step size).
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    Computing 55 (1995), S. 91-111 
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    Keywords: 65F15 (47A56) ; Nonlinear eigenvalue problem ; numerical solution ; condition number
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    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Wir betrachten die numerische Lösung des nichtlinearen EigenwertproblemsA(λ)x=0, wobei die MatrixA(λ) in nichtlinearer Weise vom Eigenwertparameter λ abhängt. Einige neue Methoden (die BDS Methoden) werden zusammen mit einer Untersuchung der Bedingungen dieser Methoden vorgestellt. Numerische Beispiele, welche diese Methoden vergleichen, werden präsentiert.
    Notes: Abstract We consider the numerical solution of the nonlinear eigenvalue problemA(λ)x=0, where the matrixA(λ) is dependent on the eigenvalue parameter λ nonlinearly. Some new methods (the BDS methods) are presented, together with the analysis of the condition of the methods. Numerical examples comparing the methods are given.
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  • 42
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    Computing 55 (1995), S. 55-73 
    ISSN: 1436-5057
    Keywords: 68P [Theory of data] ; 68P05 Data structures ; 68P20 information storage and retrieval ; Object-oriented data models ; ISA hierarchy ; complex objects ; transitive closure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung In den letzten Jahren sind viele objekt-orientierte Datenmodelle vorgeschlagen worden und dieses Gebiet ist zu einem der vielversprechendsten für die Entwicklung neuer Datenbanksysteme geworden. Bei Verwendung von komplexen Datenstrukturen, auf denen eine ISA Hierarchie definiert ist, wird effizientes Speichern and Zugreifen auf Objekte um vieles wichtiger. In dieser Arbeit schlagen wir effiziente mengenorientierte Algorithmen zur Speicherung und zum Zugriff auf komplexe Objekte in einer „Inheritance Hierarchie” vor.
    Notes: Abstract Many object oriented data models have been proposed in the past few years, and this field is one of the most promising for the development of new generation database systems. With complex data structures where an ISA hierarchy has been defined, the problem of efficiently storing and retrieving (a collection of) objects increases its relevance dramatically. This paper proposes efficient set-oriented algorithms for the storage and retrieval of complex objects in an inheritance hierarchy.
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    Computing 55 (1995), S. 75-89 
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    Keywords: 68Q20 ; 90C39 ; String edit distance ; finte state automaton ; nearest neighbor search ; doctionary lookup
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Es wird ein neuer Algorithmus für die Berechnung der Editierdistanz von Zeichenketten angegeben. Der Algorithmus beruht auf der Annahme, dass eine der beiden zu vergleichenden Zeichenketten ein a priori bekannter Eintrag in einen Wörterbuch ist. Dieser Wörterbucheintrag wird in einer off-line Phase in einen deterministischen endlichen Automaten konvertiert. Für einen gegebenen Automaten und ein Eingabewort entspricht die Berechnung der Editiordistanz einer Traversierung verschiedener Zustände dieses Automaten. Diese Prozedur benötigt Zeit, die lediglich linear von der Länge des Eingabeworts abhängt. Die Zeit ist unabhängig von der Länge des Wörterbucheintrags. Die endlichen Automaten, welche zuN verschiedenen Wörterbucheinträgen gehören, können zu einem einzigen Automaten zusammengefasst werden. Auf diese Weise benötigen die Berechnung der Editierdistanz zwischen dem Eingabewort und jedem Wörterbucheintrag sowie die Bestimmung des nächsten Nachbarn im Wörterbuch lediglich lineare Zeit hinsichtlich der Länge des Eingabeworts. Die Anzahl der Zustände des Automaten ist jedoch von exponentieller Grössenordnung.
    Notes: Abstract A new algorithm for string edit distance computation is given. The algorithm assumes that one of the two strings to be compared is a dictionary entry that is known a priori. This dictionary word is converted in an off-line phase into a deterministic finite state automaton. Given an input string and the automaton derived from the dictionary word, the computation of the edit distance between the two strings corresponds to a traversal of the states of the automaton. This procedure needs time which is only linear in the length of the input string. It is independent of the length of the dictionary word. Given not only one butN different dictionary words, their corresponding automata can be combined into a single deterministic finite state automaton. Thus the computation of the edit distance between the input word and each dictionary entry, and the determination of the nearest neighbor in the dictionary need time that is only linear in the length of the input string. However, the number os states of the automation is exponential.
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    Computing 55 (1995), S. 163-180 
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    Keywords: 65L05 ; Hopf bifurcation ; Runge-Kutta ; Poincare map
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    Description / Table of Contents: Zusammenfassung Um das Verhalten bestimmter Ein- und Mehrschrittverfahren für gewöhnliche Differentialgleichungen an schwach anziehenden Fixpunkten bzw. schwach anziehenden periodischen Lösungen zu untersuchen, wird Rückwärts-Fehleranalyse eingesetzt. Bei vielen Methoden tritt eine Hopf-Verzweigung auf; der Effekt einer adaptiven Gitteranpassung für solche Situationen wird an einem Spezialfall demonstriert.
    Notes: Abstract Backward error analysis is used to analyze the behavior of selected one-step and multi-step methods for ordinary differential equations at weakly attracting fixed points and weakly attracting periodic solutions. For many methods, a Hopf bifurcation for maps occurs. The effect of an adaptive mesh selection procedure on these results is presented for a special case.
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  • 45
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    Computing 55 (1995), S. 181-189 
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    Keywords: 65N55 ; 65F10 ; Smoothing property ; multi-grid method ; semi-iteration
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    Description / Table of Contents: Zusammenfassung Eine Modifikation des Lemmas von Reusken wird angegeben. Sie gestattet, im Falle von konvergenten Glättungsiterationen die Konvergenzgeschwindigkeit in die Abschätzung der Glättungseigenschaft mit aufzunehmen. Eine derartige Abschätzung wird bei robusten Mehrgitterverfahren benötigt. Ferner wird ein einfacher semiiterativer Glätter angegeben, der ein asymptotisch besseres Verhalten besitzt.
    Notes: Abstract A modification of the Lemma of Reusken is given. It allows us to improve the estimate of the smoothing property in cases where the contraction number of the iteration is small. This is of importance for robust multi-grid methods. Moreover, we describe a simple semi-iterative smoother with better asymptotic behaviour than for the stationary iterative smoother.
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  • 46
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    Computing 55 (1995), S. 207-221 
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    Keywords: 65COS ; 65DIS ; Particle methods ; discrepancy estimates ; nonlinear functionals
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    Description / Table of Contents: Zusammenfassung Wir betrachten die numerische Berechung nichtlinearer Funktionale von Verteilungsfunktionen, die durch Punktmaße angenähert werden. Zwei Methoden werden beschrieben und Abschätzungen für die Konvergenzgeschwindigkeit werden angegeben. Außerdem werden numerische Resultate für das Entropiefunktional vorgestellt.
    Notes: Abstract We consider the numerical computation of nonlinear functionals of distribution functions approximated by point measures. Two methods are described and estimates for the speed of convergence as the number of points tends to infinity are given. Moreover, numerical results for the entropy functional are presented.
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    Computing 55 (1995), S. 223-236 
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    Keywords: 65L05 ; 65L06 ; Runge-Kutta methods ; interpolations ; delay differential equations
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    Description / Table of Contents: Zusammenfassung Beim numerischen Lösen von Differentialgleichungen mit nacheilendem Argument (DDEs) mit Hilfe von stetigen expliziten Runge-Kutta Methoden entstehen Schwierigkeiten, wenn die Argumentverzögerung verschwindet oder zumindest kleiner als die Verfahrensschrittweite wird. In dieser Situation wird der herkömmlich explizite und sequentielle Prozeß der Stufenberechnungen des RK-Schemas ein impliziter und muß überdies iteriert werden. In dieser Arbeit werden einige Iterationsmethoden untersucht und deren Ordnung bestimmt.
    Notes: Abstract In the numerical solution of delay differential equations by a continuous explicit Runge-Kutta method a difficulty arises when the delay vanishes or becomes smaller than the stepsize the method would like to use. In this situation the standard explicit sequential process of computing the Runge-Kutta stages becomes an implicit process and an iteration scheme must be adopted. We will consider alternative iteration schemes and investigate their order.
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    Computing 55 (1995), S. I 
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    Computing 55 (1995), S. 237-253 
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    Keywords: 65N06 ; Finite difference method ; impulsive partial differential-functional equations
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    Description / Table of Contents: Zusammenfassung Wir betrachten Anfangs- und Randwertprobleme von partiellen Impuls-Differential-Funktionalgleichungen erster Ordnung. Wir leiten hinreichende Bedingungen für die Konvergenz einer allgemeinen Klasse von Einschrittmethoden her. Wir nehmen weiters an, daß die gegebenen Funktionen bezüglich ihrer Funktionalargumente einer nichtlinearen Abschätzung vom Perron-Typus genügen. Der Stabilitätsbeweis basiert auf einem Theorem über Differenzen-Funktionalgleichungen, die von einem Impuls-Differential-Funktionalproblem stammen. Grundsätzlich nehmen wir an, daß die betrachteten Funktionen die Volterra-Bedingung erfüllen. Ein numerisches Beispiel wird angeführt.
    Notes: Abstract We consider initial boundary value problems for first order impulsive partial differential-functional equations. We give sufficient conditions for the convergence of a general class of one step difference methods. We assume that given functions satisfy the non-linear estimates of the Perron type with respect to the functional argument. The proof of stability is based on a theorem on difference functional inequalities generated by an impulsive differential-functional problem. It is an essential assumption in our consideration that given functions satisfy the Volterra condition. We give a numerical example.
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    Computing 55 (1995), S. 191-206 
    ISSN: 1436-5057
    Keywords: 68Q25 ; 68U05 ; Rectangles ; balanced cuts ; separation ; binary space partition
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    Description / Table of Contents: Zusammenfassung Gegeben sei eine Menge vonn (ggf. überlappenden) isothetischen Hyperrechtecken imd-dimensionalen Raum. Diese Arbeit beschäftigt sich mit Zerlegungen dieser Hyperrechteckmenge durch Schnitthyperebenen, wobei wir annehmen, daß jedes von einer Hyperebene geschnittene Hyperrechteck in zwei nicht-überlappende Hyperrechtecke zerschnitten wird. Wir untersuchen das Verhalten einiger Balancierungskriterien für Schnitte und präsentieren optimale and praktikable Algorithmen zur Berechnung der entsprechenden balancierten Schnitte. Schließlich geben wir auch scharfe Worst-case-Schranken für die bestmöglich erreichbare Qualität der balancierten Schnitte an.
    Notes: Abstract We are given a set ofn d-dimensional (possibly intersecting) isothetic hyperrectangles. The topic of this paper is the separation of these rectangles by means of a cutting isothetic hyperplane. Thereby we assume that a rectangle which is intersected by the cutting plane iscut into two non-overlapping hyperrectangles. We investigate the behavior of several kinds of balancing functions, as well as their linear combination and present optimal and practical algorithms for computing the corresponding balanced cuts. In addition, we give tight worst-case bounds for the quality of the balanced cuts.
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    Computing 55 (1995), S. 271-288 
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    Keywords: 65F10 ; Finite elements ; multigrid methods ; error control
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    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Wir behandeln das Problem einer adaptiven Fehlerkontrolle bei Finite-Elemente-Methoden unter Enschluß des Fehlers, der durch ungenaue Lösung der diskreten Gelichungen entsteht. Wir beweisen A-posteriori-Fehlerabschätzungen für ein elliptisches Modellproblem, welches mit linearen finiten-Elementen diskretisiert wird. Die diskreten Gleichungen werden mit Hilfe des kanonischen Finite-Elemente-Mehrgitterverfahrens gelöst. Die Beweise beruhen auf der Kombination der «starken” stabilitätseigenschaft des zugrundeliegenden Differentialoperators und der Galerkin-Orthogonalität sowohl des Finite-Elemente-als auch des Mehrgitterverfahrens.
    Notes: Abstract We consider the problem of adaptive error control in the finite element method including the error resulting from, inexact solution of the discrete equations. We prove a posteriori error estimates for a prototype elliptic model problem discretized by the finite element with a canomical multigrid algorithm. The proofs are based on a combination of so-called strong stability and, the orthogonality inherent in both the finite element method can the multigrid algorithm.
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    Computing 55 (1995), S. 289-304 
    ISSN: 1436-5057
    Keywords: 65N15 ; 65N30 ; 65N50 ; Adaptive mesh refinement ; a posteriori error estimate ; nonlinear Poisson equation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Wir entwickeln adaptive Methoden zur Berechnung von Finite Elemente-Lösungen der Partiellen Differentialgleichung −Δu=f(u) auf einem beschränktem Gebiet Ω ⊆ ℝ2. In der Praxis arbeitet man mit einer Approximationf h vonf, was zu falschen Ergebnissen führen kann, wenn man den zugehörigen Approximationsfehler auf dem groben Gitter nicht mitberücksichtigt. Wir verwenden eine Strategie, die zu Beginn der Iteration robust aber weniger effizient ist und gehen zu effektiveren Methoden über, falls gewisse Sättigungsbedingungen erfühlt sind. Dazu leiten wir a posteriori Fehlerschranken und a posteriori Sättigungsbedingungen her, um die Qualität der numerischen Lösung zu beurteilen.
    Notes: Abstract Our goal is to develop adaptive strategies in order to obtain finite element solutions of the partial differential equation-Δu=f(u) in a bounded domain Ω ⊆ ℝ2. In practice one works with an approximationf h off. But this may give wrong results if we do not control the coresponding approximation error on coarse girds. In this work we develop a strategy that is robust, but less efficient, in the beginning of the adaptive algorithm and switches to a more efficient procedure if certainsaturation conditions are satisfied. The results are based on a posteriori saturation criterial that measure the quality of the approximation solution.
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    Engineering with computers 11 (1995), S. 94-102 
    ISSN: 1435-5663
    Keywords: Rational cubic ; Bernstein-Bézier ; Shape control ; Tension
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract This paper is concerned with the problem of fitting curves and surfaces, for computer aided design (CAD), via an ordered set of control points, so that the result is satisfactory for the user's needs. Piecewise rational functions with cubic numerator and quadratic denominator are used in the construction of the scheme, in such a way that the descriptions of the parameters control the shape of the picture in the desired area. A general solution is obtained for points inN-space, although the scheme is only meaningful in the cases whereN=2 andN=3.
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    Engineering with computers 11 (1995), S. 145-156 
    ISSN: 1435-5663
    Keywords: Database ; Date fusson ; Date model ; Information architecture ; Information model ; Manufacturing ; Sensors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Data fusion is the integration and analysis of data from multiple sensors to develop a more accurate understanding of a situation and determine how to respond to it. Although data fusion can be applied in many situations, this paper focuses on its application to manufacturing and how it changes some of the more traditional, less adaptive information models that support the design and manufacturing functions. The paper consists of four parts. The first section explains what data fusion is and its impact on manufacturing. The second section describes what an information system architecture is and explains the natural language-based information modeling methodology used by this research project. The third section identifies the major design and manufacturing functions, reviews the information models required to support them, and then shows how these models must be extended to support data fusion. The fourth section discusses the future directions of this work.
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    Engineering with computers 11 (1995), S. 167-172 
    ISSN: 1435-5663
    Keywords: Concurrent engineering ; Configuration management ; Data model ; Design Process ; Engineering data management ; Product data management
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    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract In order to make the traditional product structure tree representation amenable to concurrent engineering relationships likeperspective-of anddependent-on have to be added to the essentialpart-of relationship. Complex data can be held in proprietary formats, while simple data will be in a common representation for direct access by diverse disciplines. Coordination among team members in a project can be carried out using such a model. Besides, a virtually unified view of all the data is possible, though they may lie in distributed and heterogeneous data bases. A very necessary characteristic of such a model is that its time evolution should be easy to represent in order to reflect the dynamic nature of product development, where the model itself, and not merely the data values change. Managing versions is also facilitated by the comprehensive structure of the Unified Product Data Model (UPDM).
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    Engineering with computers 11 (1995), S. 227-245 
    ISSN: 1435-5663
    Keywords: Conceptual design ; Design process ; Design studies ; Engineering information systems ; Product data
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract This paper identifies requirements for an engineering design information management system. Future CAD systems must support a wide range of activities — such as definition, manipulation and analyses of complex product information models. These models represent not only conventional data associated with current CAD applications, but also design information characterizing the correlations between the requirements, functions, behaviors and physical form of the product. Such functionality is important for both the individual designer and the design organization, as the need to manage information as a corporate asset is becoming a critical component of business strategy. This paper explores these needs using two design studies. The first study illustrates some major concepts relative to non-routine design activities, while the second study focuses on the routine design activities relative to organization interactions. These studies were used to elicit high level requirements which serve as the basis for the development of prototype software systems. These prototypes are briefly introduced here.
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    Engineering with computers 11 (1995), S. 213-226 
    ISSN: 1435-5663
    Keywords: Communication channel ; Communication path ; Data attribute ; Design object ; Method group ; Object-oriented ; Receiving interface ; Relationship ; Relationship attribute ; Sending method
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    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Technology
    Notes: Abstract Object-oriented principles have introduced several useful concepts for developing complex software systems. As a result, several methodologies have been suggested for the overall design of software systems based on these concepts. Methodologies and frameworks for designing objects that are to be part of the software systems are currently lacking. This paper proposes anobject design framework andmethodology, which utilizes the object-oriented concepts, for planning, organizing and designing structural engineering design objects. Design objects in an integrated structural engineering system are complex and often related to each other in various different ways. The paper also identifies several important relationships among structural engineering design objects. These relationships serve as communication channels through wich design objects send messages to and receive responses from each other. Several examples, drawn from reinforced concrete structures, will be presented to demonstrate the object design methodology and to illustrate how the framework is effective in reducing the complexity of design objects in an integrated structural engineering system.
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    AI & society 9 (1995), S. 18-28 
    ISSN: 1435-5655
    Keywords: Ethics ; Science ; Technology
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    Topics: Computer Science
    Notes: Abstract In the paper, three propositions are put forward. First, that intellectual structures of wide scope commonly lead to conclusions which are ethically unacceptable; secondly that the ethically unacceptable consequences of science arise from one particular presupposition which it adopts, namely that of causality; thirdly, that causality is no essential part of science.
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    AI & society 9 (1995), S. 29-42 
    ISSN: 1435-5655
    Keywords: Skills ; Deskilling ; Communication ; Control ; Privacy ; Identity ; Ethical neutrality ; Discourse ; Responsibility
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract This paper first illustrates what kind of ethical issues arise from the new information, communication and automation technology. It then argues that we may embrace the popular idea that technology is ethically neutral or even ambivalent without having to close our eyes to those issues and in fact, that the ethical neutrality of technology makes them all the more urgent. Finally, it suggests that the widely ignored fact of normal responsible behaviour offers a new and fruitful starting point for any future thinking about such issues.
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    AI & society 9 (1995), S. 80-90 
    ISSN: 1435-5655
    Keywords: Computing ; Ethics ; Feminism ; Healthcare
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    Topics: Computer Science
    Notes: Abstract Value in the British National Health Service have shifted away from patient care towards financial control. However, in the quest for “efficiency”, huge amounts of NHS money have been wasted on computer system which failed. In this paper, I draw on a case study to explore some of the ethical issues which underlie this kind of waste of resources. Issues include the gap between public pronouncements and personal experience, the chaos of which lies behind the facade of rationality, and the systematic silencing of people, usually women, who question the viability of computer systems which are created for private gain rather than public service.
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    Keywords: User-centred design ; Allocation of function ; Expert systems ; Iteration ; Prototype
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    Topics: Computer Science
    Notes: Abstract A case study is presented of the development of computer-based support tools for power engineers in the electricity supply industry. The objective was to develop an expert system to support witching schedule production. A user-centred approach was followed which led the user community to conclude that a switching schedule production assistant (SSPA) was required which would leave control with the power engineer. Prototype systems were developed and evaluated in user trials which revealed that a significant and more general purpose tool would be a computer generated electricity network display that the engineers could manipulate. The paper concludes that the process of enabling users to evaluate alternative forms of technology can facilitate the development systems that are useful, acceptable and usable.
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    AI & society 9 (1995), S. 115-115 
    ISSN: 1435-5655
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    AI & society 9 (1995), S. 258-272 
    ISSN: 1435-5655
    Keywords: Action ; Design ; Discourse ; Innovation ; Language ; Methodology ; Tacit knowledge
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract This contribution to design methodology reflects upon the barriers to effectiveness imposed by our tendency to gravitate towards the over-formal in human affairs. We see a correspondingly cleaned-up description of the process of design, a failure to consider its jagged elements and to take proper account of the non-formal in knowledge (e.g. tacit knowledge) and communication. Discipline in methodology is accordingly wrongly equated with formality. The failure of design to be effective is more likely for innovative design rather than routine design. It is suggested by way of explanation that design methodology especially in the field of information technology is infused with the ghost of positivism, manifest in an unconditional belief in the value of rationality and an implied naive realist conviction about the fixed, singular and transparent nature of the environment for which design is undertaken. We need to be able to work with uncertainty rather than try for its entire elimination. A breadth of approach in carrying out the activity of design is threatened by lack of attention to the variety of forms which knowledge and corresponding forms of discourse can take. We undertake the disciplined reduction from the messy real work to metaphors tidy enough to work with, or models as they are usually misnamed. The notion of “language of struggle” is invoked as a suitable metaphor for the non-formal discourse particularly relevant to innovative design. A complementary exploration is offered of socio-linguistic space which is the common context for design. In view of the concern with social space necessary to effective design, it may be enlightening to consider the designer as applied anthropologist.
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    AI & society 9 (1995), S. 373-388 
    ISSN: 1435-5655
    Keywords: Hypermedia ; CSCW design ; CSCW analysis ; Synchronous ; Asynchronous ; Remote ; Co-located
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    Topics: Computer Science
    Notes: Abstract The paper presents a general critique of the use of conceptual frameworks in design, illustrated by the well known synchronous/asynchronous, co-located/non-co-located framework. It argues that while frameworks are a necessary and inevitable starting point for design, the business of tailoring and adapting them to specific situations need not be ad hoc.Triggering artefacts are a way of systematically challenging both designers' preunderstandings and the conservatism of work practice. Experiences from the Great Belt tunnel and bridge project are used to illustrate howtriggering artefacts change themodality of designing for change.
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    AI & society 9 (1995), S. 389-395 
    ISSN: 1435-5655
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract The question whether or not computers can think was first asked in print by Alan Turing in his seminal 1950 article. In order to avoid defining what a computer is or what thinking is, Turing resorts to “the imitation game” which is a test that allows us to determine whether or not a machine can think. That is, if an interrogator is unable to tell whether responses to his questions come from a human being or from a machine, the machine is imitating a human being so well that it has to be acknowledged that these responses result from its thinking. However, then as now, it is not an indisputable claim that machines could think, and an unceasing stream of papers discussing the validity of the test proves this point. There are many arguments in favour of, as well as against, the claims borne by the test, and Turing himself discusses some of them. In his view, there are mice possible objections to the concept of a thinking machine, which he eventually dismisses as weak, irrelevant, or plain false. However, as he admits, he can present “no very convincing arguments of a positive nature to support my views. If I had I should not have taken such pains to point out the fallacies in contrary views”.
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    AI & society 9 (1995), S. 396-401 
    ISSN: 1435-5655
    Keywords: Software crisis ; AI software engineering ; Human-centred software design ; Kantian philosophy ; Constructivism ; Human thinking models
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract In this article I deal with the question “How could we renew and enrich computer technology with Kant's help?”. By this I would like to invite computer scientists and engineers to initiate or intensify their cooperation with Kant experts. What I am looking for is a better “method of definition” for software systems, particularly for the development of object-oriented and knowledge-based systems. After a description of the “software crisis”, I deal first with the question why this crisis could not yet be overcome. A way out of this software crisis can be expected from systems which are adapted to the human faculty of thinking. I show which foundation is in my opinion necessary and sketch the principles according to which a “human-centred” method of definition for sych systems could be developed on that foundation with Kant's help.
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    Mathematical programming 68 (1995), S. 1-13 
    ISSN: 1436-4646
    Keywords: Transportation problem ; Strongly polynomial algorithm ; Excess scaling
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    Topics: Computer Science , Mathematics
    Notes: Abstract For the (linear) transportation problem withm supply nodes,n demand nodes andk feasible arcs we describe an algorithm which runs in time proportional tom logm(k + n logn) (assuming w.l.o.g.m⩾n). The algorithm uses excess scaling. The complexity bound is a slight improvement over the bound achieved by an application of a min-cost-flow algorithm of Orlin to the transportation problem.
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    Mathematical programming 68 (1995), S. 49-71 
    ISSN: 1436-4646
    Keywords: Power-series interior point algorithms: Parameter transformations ; Best parameter ; k-parameter ; Truncated power-series approximation ; Higher-order derivatives ; Linear programming
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract In this paper we study higher-order interior point algorithms, especially power-series algorithms, for solving linear programming problems. Since higher-order differentials are not parameter-invariant, it is important to choose a suitable parameter for a power-series algorithm. We propose a parameter transformation to obtain a good choice of parameter, called ak-parameter, for general truncated powerseries approximations. We give a method to find ak-parameter. This method is applied to two powerseries interior point algorithms, which are built on a primal—dual algorithm and a dual algorithm, respectively. Computational results indicate that these higher-order power-series algorithms accelerate convergence compared to first-order algorithms by reducing the number of iterations. Also they demonstrate the efficiency of thek-parameter transformation to amend an unsuitable parameter in power-series algorithms.
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    Mathematical programming 68 (1995), S. 187-203 
    ISSN: 1436-4646
    Keywords: Linear complementarity problem ; Co-positive ; Semi-monotone ; Q-matrix ; R 0-matrix
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    Topics: Computer Science , Mathematics
    Notes: Abstract In this paper we consider not necessarily symmetric co-positive as well as semi-monotoneQ-matrices and give a set of sufficient conditions for such matrices to beR 0-matrices. We give several examples to show the sharpness of our results. Construction of these examples is based on the following elementary proposition: IfA is a square matrix of ordern whose first two rows are identical and bothA 11 andA 22 areQ-matrices whereA ii stands for the principal submatrix ofA obtained by deleting rowi and columni fromA, thenA is aQ-matrix.
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    Mathematical programming 68 (1995), S. 213-237 
    ISSN: 1436-4646
    Keywords: Mixed-integer programming ; Multicommodity flows
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    Topics: Computer Science , Mathematics
    Notes: Abstract The following problem arises in the study of lightwave networks. Given a demand matrix containing amounts to be routed between corresponding nodes, we wish to design a network with certain topological features, and in this network, route all the demands, so that the maximum load (total flow) on any edge is minimized. As we show, even small instances of this combined design/routing problem are extremely intractable. We describe computational experience with a cutting plane algorithm for this problem.
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    Mathematical programming 68 (1995), S. 267-301 
    ISSN: 1436-4646
    Keywords: Nonlinear programming ; Trust-region methods ; Global convergence
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    Notes: Abstract We present a trust-region method for minimizing a general differentiable function restricted to an arbitrary closed set. We prove a global convergence theorem. The trust-region method defines difficult subproblems that are solvable in some particular cases. We analyze in detail the case where the domain is a Euclidean ball. For this case we present numerical experiments where we consider different Hessian approximations.
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    Mathematical programming 68 (1995), S. 319-346 
    ISSN: 1436-4646
    Keywords: Nonsmooth optimization ; Trust region methods ; global convergence
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    Notes: Abstract This paper investigates the global convergence of trust region (TR) methods for solving nonsmooth minimization problems. For a class of nonsmooth objective functions called regular functions, conditions are found on the TR local models that imply three fundamental convergence properties. These conditions are shown to be satisfied by appropriate forms of Fletcher's TR method for solving constrained optimization problems, Powell and Yuan's TR method for solving nonlinear fitting problems, Zhang, Kim and Lasdon's successive linear programming method for solving constrained problems, Duff, Nocedal and Reid's TR method for solving systems of nonlinear equations, and El Hallabi and Tapia's TR method for solving systems of nonlinear equations. Thus our results can be viewed as a unified convergence theory for TR methods for nonsmooth problems.
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    Mathematical programming 69 (1995), S. 89-109 
    ISSN: 1436-4646
    Keywords: Nondifferentiable (nonsmooth) optimization ; Convex programming ; Mathematical programming ; Nonlinear programming ; Saddle-points ; Variational inequalities ; Bundle methods
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    Notes: Abstract We study proximal level methods for convex optimization that use projections onto successive approximations of level sets of the objective corresponding to estimates of the optimal value. We show that they enjoy almost optimal efficiency estimates. We give extensions for solving convex constrained problems, convex-concave saddle-point problems and variational inequalities with monotone operators. We present several variants, establish their efficiency estimates, and discuss possible implementations. In particular, our methods require bounded storage in contrast to the original level methods of Lemaréchal, Nemirovskii and Nesterov.
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    Mathematical programming 69 (1995), S. 111-147 
    ISSN: 1436-4646
    Keywords: Nonsmooth convex optimization ; Bundle methods
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    Notes: Abstract In this paper we describe a number of new variants of bundle methods for nonsmooth unconstrained and constrained convex optimization, convex—concave games and variational inequalities. We outline the ideas underlying these methods and present rate-of-convergence estimates.
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    Mathematical programming 69 (1995), S. 255-268 
    ISSN: 1436-4646
    Keywords: Generalized linear complementarity problem ; Piecewise linear systems ; Multiple objective programming ; Variational inequalities ; NP-complete
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    Notes: Abstract We show that the Cottle—Dantzig generalized linear complementarity problem (GLCP) is equivalent to a nonlinear complementarity problem (NLCP), a piecewise linear system of equations (PLS), a multiple objective programming problem (MOP), and a variational inequalities problem (VIP). On the basis of these equivalences, we provide an algorithm for solving problem GLCP.
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    Mathematical programming 69 (1995), S. 205-236 
    ISSN: 1436-4646
    Keywords: Interior point algorithms ; Linear matrix inequalities ; Semidefinite programming
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    Notes: Abstract We describe a potential reduction method for convex optimization problems involving matrix inequalities. The method is based on the theory developed by Nesterov and Nemirovsky and generalizes Gonzaga and Todd's method for linear programming. A worst-case analysis shows that the number of iterations grows as the square root of the problem size, but in practice it appears to grow more slowly. As in other interior-point methods the overall computational effort is therefore dominated by the least-squares system that must be solved in each iteration. A type of conjugate-gradient algorithm can be used for this purpose, which results in important savings for two reasons. First, it allows us to take advantage of the special structure the problems often have (e.g., Lyapunov or algebraic Riccati inequalities). Second, we show that the polynomial bound on the number of iterations remains valid even if the conjugate-gradient algorithm is not run until completion, which in practice can greatly reduce the computational effort per iteration. We describe in detail how the algorithm works for optimization problems withL Lyapunov inequalities, each of sizem. We prove an overallworst-case operation count of O(m 5.5L1.5). Theaverage-case complexity appears to be closer to O(m 4L1.5). This estimate is justified by extensive numerical experimentation, and is consistent with other researchers' experience with the practical performance of interior-point algorithms for linear programming. This result means that the computational cost of extending current control theory based on the solution of Lyapunov or Riccatiequations to a theory that is based on the solution of (multiple, coupled) Lyapunov or Riccatiinequalities is modest.
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    Mathematical programming 69 (1995), S. 311-333 
    ISSN: 1436-4646
    Keywords: Interior-point methods ; Primal-dual affine scaling ; Linear programming ; Linear complementarity
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    Notes: Abstract We describe an interior-point algorithm for monotone linear complementarity problems in which primal-dual affine scaling is used to generate the search directions. The algorithm is shown to have global and superlinear convergence with Q-order up to (but not including) two. The technique is shown to be consistent with a potential-reduction algorithm, yielding the first potential-reduction algorithm that is both globally and superlinearly convergent.
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    Mathematical programming 69 (1995), S. 403-411 
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    Keywords: Nonconvex quadratic programming ; Local minimum ; NP-complete ; Necessary and sufficient condition
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    Notes: Abstract The author (1992, 1993) earlier studied the equivalence of a class of 0–1 quadratic programs and their relaxed problems. Thus, a class of combinatorial optimization problems can be solved by solving a class of nonconvex quadratic programs. In this paper, a necessary and sufficient condition for local minima of this class of nonconvex quadratic programs is given; this will be the foundation for study of algorithms.
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    Mathematical programming 69 (1995), S. 449-470 
    ISSN: 1436-4646
    Keywords: k-Matroid Intersection Problem ; Matroidk-Parity Problem ; Hyperdeterminant
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    Notes: Abstract We present algorithms for thek-Matroid Intersection Problem and for the Matroidk-Parity Problem when the matroids are represented over the field of rational numbers andk 〉 2. The computational complexity of the algorithms is linear in the cardinality and singly exponential in the rank of the matroids. As an application, we describe new polynomially solvable cases of thek-Dimensional Assignment Problem and of thek-Dimensional Matching Problem. The algorithms use some new identities in multilinear algebra including the generalized Binet—Cauchy formula and its analogue for the Pfaffian. These techniques extend known methods developed earlier fork = 2.
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    Mathematical programming 69 (1995), S. vii 
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    Mathematical programming 70 (1995), S. 17-25 
    ISSN: 1436-4646
    Keywords: Flow ; Cuts ; Polyhedral combinatorics
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    Notes: Abstract Consider the polyhedron represented by the dual of the LP formulation of the maximums–t flow problem. It is well known that the vertices of this polyhedron are integral, and can be viewed ass–t cuts in the given graph. In this paper we show that not alls–t cuts appear as vertices, and we give a characterization. We also characterize pairs of cuts that form edges of this polyhedron. Finally, we show a set of inequalities such that the corresponding polyhedron has as its vertices alls–t cuts.
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    Mathematical programming 70 (1995), S. 73-89 
    ISSN: 1436-4646
    Keywords: Stochastic integer programming ; Parametric integer programming ; Continuity ; Stability ; Weak convergence of probability measures
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    Notes: Abstract For two-stage stochastic programs with integrality constraints in the second stage, we study continuity properties of the expected recourse as a function both of the first-stage policy and the integrating probability measure. Sufficient conditions for lower semicontinuity, continuity and Lipschitz continuity with respect to the first-stage policy are presented. Furthermore, joint continuity in the policy and the probability measure is established. This leads to conclusions on the stability of optimal values and optimal solutions to the two-stage stochastic program when subjecting the underlying probability measure to perturbations.
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    Mathematical programming 70 (1995), S. 149-157 
    ISSN: 1436-4646
    Keywords: Parametric optimization ; Semi-infinite programming ; Convex programming ; Optimal value function ; Directional differentiability
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    Notes: Abstract In this paper, directional differentiability properties of the optimal value function of a parameterized semi-infinite programming problem are studied. It is shown that if the unperturbed semi-infinite programming problem is convex, then the corresponding optimal value function is directionally differentiable under mild regularity assumptions. A max-min formula for the directional derivatives, well-known in the finite convex case, is given.
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  • 84
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    Mathematical programming 70 (1995), S. 173-190 
    ISSN: 1436-4646
    Keywords: Lagrangian relaxation ; Slack variables ; Scheduling
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    Notes: Abstract Lagrangian relaxation is a powerful bounding technique that has been applied successfully to manyNP-hard combinatorial optimization problems. The basic idea is to see anNP-hard problem as an “easy-to-solve” problem complicated by a number of “nasty” side constraints. We show that reformulating nasty inequality constraints as equalities by using slack variables leads to stronger lower bounds. The trick is widely applicable, but we focus on a broad class of machine scheduling problems for which it is particularly useful. We provide promising computational results for three problems belonging to this class for which Lagrangian bounds have appeared in the literature: the single-machine problem of minimizing total weighted completion time subject to precedence constraints, the two-machine flow-shop problem of minimizing total completion time, and the single-machine problem of minimizing total weighted tardiness.
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    Mathematical programming 70 (1995), S. 233-249 
    ISSN: 1436-4646
    Keywords: Nondifferentiable optimization ; Composite NDO ; Basic NDO ; Second-order convergence ; Global convergence ; Polyhedral approximation ; Convex programming
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    Notes: Abstract There are two main classes of iterative methods in nondifferentiable optimization (NDO). In thebasic NDO, the information is limited to the objective function and at least one element of its subdifferential, while in thecomposite NDO, the objective function is split into a sum of a smooth and a nonsmooth function. Our work unifies these two approaches for benefiting of their respective advantages.
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    Mathematical programming 71 (1995), S. 1-15 
    ISSN: 1436-4646
    Keywords: 0–1 polytopes ; Ideal polytopes ; Heuristic ; Maximum stable set problem
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    Notes: Abstract Given a finite setX and a family of “feasible” subsetsF ofX, the 0–1 polytope P (F is defined as the convex hull of all the characteristic vectors of members ofF We show that under a certain assumption a special type of face ofP(F) is equivalent to the ideal polytope of some pseudo-ordered set. Examples of families satisfying the assumption are those related to the maximum stable set problem, set packing and set partitioning problems, and vertex coloring problem. Using this fact, we propose a new heuristic for such problems and give results of our preliminary computational experiments for the maximum stable set problem.
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  • 87
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    Mathematical programming 71 (1995), S. 113-126 
    ISSN: 1436-4646
    Keywords: Polyhedral combinatorics ; Packing subtrees ; Knapsacks with precedence ; Column generation ; Dynamic programming
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract Given a treeG = (V, E) and a weight function defined on subsets of its nodes, we consider two associated problems. The first, called the “rooted subtree problem”, is to find a maximum weight subtree, with a specified root, from a given set of subtrees. The second problem, called “the subtree packing problem”, is to find a maximum weight packing of node disjoint subtrees chosen from a given set of subtrees, where the value of each subtree may depend on its root. We show that the complexity status of both problems is related, and that the subtree packing problem is polynomial if and only if each rooted subtree problem is polynomial. In addition we show that the convex hulls of the feasible solutions to both problems are related: the convex hull of solutions to the packing problem is given by “pasting together” the convex hulls of the rooted subtree problems. We examine in detail the case where the set of feasible subtrees rooted at nodei consists of all subtrees with at mostk nodes. For this case we derive valid inequalities, and specify the convex hull whenk ⩽ 4.
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    Mathematical programming 71 (1995), S. 179-194 
    ISSN: 1436-4646
    Keywords: Gauss—Newton ; Convex composite optimization ; Weak sharp minima ; Quadratic convergence
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    Topics: Computer Science , Mathematics
    Notes: Abstract An extension of the Gauss—Newton method for nonlinear equations to convex composite optimization is described and analyzed. Local quadratic convergence is established for the minimization ofh ο F under two conditions, namelyh has a set of weak sharp minima,C, and there is a regular point of the inclusionF(x) ∈ C. This result extends a similar convergence result due to Womersley (this journal, 1985) which employs the assumption of a strongly unique solution of the composite functionh ο F. A backtracking line-search is proposed as a globalization strategy. For this algorithm, a global convergence result is established, with a quadratic rate under the regularity assumption.
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    Mathematical programming 71 (1995), S. 247-247 
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    Mathematical programming 71 (1995), S. 327-351 
    ISSN: 1436-4646
    Keywords: Variational inequalities ; Nonlinear programming ; Complexity analysis ; Monotone operators
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    Notes: Abstract In this paper, we propose a concept of polynomiality for variational inequality problems and show how to find a near optimal solution of variational inequality problems in a polynomial number of iterations. To establish this result, we build upon insights from several algorithms for linear and nonlinear programs (the ellipsoid algorithm, the method of centers of gravity, the method of inscribed ellipsoids, and Vaidya's algorithm) to develop a unifying geometric framework for solving variational inequality problems. The analysis rests upon the assumption of strong-f-monotonicity, which is weaker than strict and strong monotonicity. Since linear programs satisfy this assumption, the general framework applies to linear programs.
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    Mathematical programming 71 (1995), S. 259-288 
    ISSN: 1436-4646
    Keywords: Complexity of linear programming ; Approximate data ; Approximate solutions ; Condition measures ; Knowledge
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    Notes: Abstract An algorithm that gives an approximate solution of a desired accuracy to a system of linear inequalities specified with approximate data is presented. It uses knowledge that the actual instance is feasible to reduce the data precision necessary to give an approximate solution to the actual instance. In some cases, this additional information allows problem instances that are ill-posed without the knowledge of feasibility to be solved. The algorithm is computationally efficient and requires not much more data accuracy than the minimal amount necessary to give an approximate solution of the desired accuracy. This work aids in the development of a computational complexity theory that uses approximate data and knowledge.
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    Graphs and combinatorics 11 (1995), S. 213-220 
    ISSN: 1435-5914
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    Notes: Abstract A graphG isconvergent when there is some finite integern ≥ 0, such that then-th iterated clique graphK n(G) has only one vertex. The smallest suchn is theindex ofG. TheHelly defect of a convergent graph is the smallestn such thatK n(G) is clique Helly, that is, its maximal cliques satisfy the Helly property. Bandelt and Prisner proved that the Helly defect of a chordal graph is at most one and asked whether there is a graph whose Helly defect exceeds the difference of its index and diameter by more than one. In the present paper an affirmative answer to the question is given. For any arbitrary finite integern, a graph is exhibited, the Helly defect of which exceeds byn the difference of its index and diameter.
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    Graphs and combinatorics 11 (1995), S. 245-248 
    ISSN: 1435-5914
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    Notes: Abstract An extension of Hall's theorem is proved, which gives a condition for complete matchings in a certain class of hypergraphs.
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    Graphs and combinatorics 11 (1995), S. 249-254 
    ISSN: 1435-5914
    Keywords: perfect ; minimal imperfect ; Berge ; star cutset ; unbreakable ; disc ; weakly chordal ; weakly triangulated
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    Notes: Abstract We show that every vertex in an unbreakable graph is in a disc, where a disc is a chordless cycle, or the complement of a chordless cycle, with at least five vertices. A corollary is that every vertex in a minimal imperfect graph is in a disc.
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    Graphs and combinatorics 11 (1995), S. 21-28 
    ISSN: 1435-5914
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    Notes: Abstract We prove (a generalization of) the following conjecture of R. Häggkvist: LetG be a 2-connected graph onn vertices where every pair of nonadjacent vertices has degree sum at leastn — k and assume thatG has ak-factor; thenG is hamiltonian. This result is a common generalization of well-known theorems of Ore and Jackson, respectively.
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    Graphs and combinatorics 11 (1995), S. 49-52 
    ISSN: 1435-5914
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    Notes: Abstract A graphG is called a block—cactus graph if each block ofG is complete or a cycle. In this paper, we shall show that a block—cactus graphG has the property that the cardinality of a smallest set separating any vertex setJ ofG is the maximum number of internally disjoint paths between the vertices ofJ if and only if every block ofG contains at most two cut-vertices. This result extends two theorems of Sampathkumar [4] and [5].
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    Graphs and combinatorics 11 (1995), S. 389-396 
    ISSN: 1435-5914
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    Notes: Abstract LetG be a graph of ordern ≥ 6 with minimum degree at least ⌈(n + 1)/2⌉. Then, for any two integerss andt withs ≥ 3,t ≥ 3 ands + t ≤ n, G contains two vertex-disjoint cycles of lengthss andt, respectively, unless thatn, s andt are odd andG is isomorphic toK (n−1)/2,(n−1)/2 + K1. We also show that ifG is a graph of ordern ≥ 8 withn even and minimum degree at leastn/2, thenG contains two vertex-disjoint cycles with any given even lengths provided that the sum of the two lengths is at mostn.
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    Graphs and combinatorics 11 (1995), S. 347-366 
    ISSN: 1435-5914
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    Notes: Abstract LetX be a set ofv + 1 elements, wherev ≡ 0 or 1 (mod 3). If two copies of the collection of $$\left( {\begin{array}{*{20}c} {v + 1} \\ 3 \\ \end{array} } \right)$$ triples chosen fromX can be partitioned intov + 1 mutually disjoint two-fold triple systems, each based on a differentv-subset ofX, we say they form an overlarge set of two-fold triple systems, denoted byOS(TTS(v)). In this paper, we give the first construction of anOS(TTS(10)). We then investigate the properties of the uniqueOS(TTS(6)) and obtain: (i) A partition of the set of 84 distinctTTS(6) based onX = {1, 2,..., 7} into 12 parallel classes, that is, into 12OS(TTS(6)) each containing sevenTTS(6); (ii) A resolution of the set of 1008 distinctOS(TTS(6)) based onX into 84 parallel classes; (iii) Simple constructions of several strongly-regular graphs, including both the Hoffman-Singleton and Higman-Sims graphs, which arise from the relation between the family of 84 distinctTTS(6) and the family of 30 distinctSTS(7), all based onX.
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  • 99
    ISSN: 1572-8102
    Keywords: The computer industry, standards, Futurebus+ ; multiple data stream architectures, interconnection architectures ; network protocols, protocol verification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract We used a hardware description language to construct a formal model of the cache coherence protocol described in the IEEE Futurebus+standard. By applying temporal logic model checking techniques, we found errors in the standard. The result of our project is a concise, comprehensible and unambiguous model of the protocol that should be useful both to the Futurebus+Working Group members, who are responsible for the protocol, and to actual designers of Futurebus+boards.
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    Formal methods in system design 6 (1995), S. 295-320 
    ISSN: 1572-8102
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    Topics: Computer Science
    Notes: Abstract This paper describes a verification technique that 1) enables a designer to verify properties of a partial design where some parts have not yet been completed, 2) yields a number of verification conditions growing linearly with the size of the design description. The technique was developed as part of work aimed at providing high-level tools for specification, verification, analysis, and synthesis of circuit descriptions written in a design language calledSynchronized Transitions [18]. The verification is supported by the mechanical theorem proverlp [5, 10].
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