ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
Filter
  • Articles  (15,041)
  • Springer  (15,041)
  • American Chemical Society
  • 1995-1999  (15,041)
  • Computer Science  (15,041)
Collection
  • Articles  (15,041)
Years
Year
Journal
  • 1
    Electronic Resource
    Electronic Resource
    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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 2
    Electronic Resource
    Electronic Resource
    Springer
    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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 69 (1995), S. 45-73 
    ISSN: 1436-4646
    Keywords: Cutting plane ; Stochastic programming ; Analytic center ; Interior-point method
    Source: Springer Online Journal Archives 1860-2000
    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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 4
    Electronic Resource
    Electronic Resource
    Springer
    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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 5
    Electronic Resource
    Electronic Resource
    Springer
    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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 6
    Electronic Resource
    Electronic Resource
    Springer
    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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 7
    Electronic Resource
    Electronic Resource
    Springer
    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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 8
    Electronic Resource
    Electronic Resource
    Springer
    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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 9
    Electronic Resource
    Electronic Resource
    Springer
    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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 70 (1995), S. 191-200 
    ISSN: 1436-4646
    Keywords: Strictly pseudomonotone map ; Z-map ; Complementarity problem ; Least element problem
    Source: Springer Online Journal Archives 1860-2000
    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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 11
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 70 (1995), S. 251-277 
    ISSN: 1436-4646
    Keywords: Linear programming ; Barrier methods ; Interior-point methods
    Source: Springer Online Journal Archives 1860-2000
    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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 13
    Electronic Resource
    Electronic Resource
    Springer
    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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 14
    Electronic Resource
    Electronic Resource
    Springer
    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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 15
    Electronic Resource
    Electronic Resource
    Springer
    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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 16
    Electronic Resource
    Electronic Resource
    Springer
    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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 17
    Electronic Resource
    Electronic Resource
    Springer
    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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 18
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 71 (1995), S. 195-206 
    ISSN: 1436-4646
    Keywords: Superfluous matrix ; Linear complementarity problem
    Source: Springer Online Journal Archives 1860-2000
    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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 19
    Electronic Resource
    Electronic Resource
    Springer
    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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 20
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 71 (1995), S. 369-370 
    ISSN: 1436-4646
    Keywords: Local Lipschitz property ; Infinite-dimensional Hilbert space
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract An oversight in a paper of Correa and Lemaréchal (this journal, 1993) is noted; a counterexample is given.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 21
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 80 (1998), S. 17-33 
    ISSN: 1436-4646
    Keywords: Dual simplex method ; Maximum flow ; Strongly polynomial ; Preflow algorithm ; Valid distance labels
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract This paper presents dual network simplex algorithms that require at most 2nm pivots and O(n 2 m) time for solving a maximum flow problem on a network ofn nodes andm arcs. Refined implementations of these algorithms and a related simplex variant that is not strictly speaking a dual simplex algorithm are shown to have a complexity of O(n 3). The algorithms are based on the concept of apreflow and depend upon the use of node labels that are underestimates of the distances from the nodes to the sink node in the extended residual graph associated with the current flow. © 1998 The Mathematical Programming Society, Inc. Published by Elsevier Science B.V.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 22
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 80 (1998), S. 35-61 
    ISSN: 1436-4646
    Keywords: Graph partitioning ; Linear programming ; Bundle method ; Parallel optimization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract This paper describes heuristics for partitioning a generalM × N matrix into arrowhead form. Such heuristics are useful for decomposing large, constrained, optimization problems into forms that are amenable to parallel processing. The heuristics presented can be easily implemented using publicly available graph partitioning algorithms. The application of such techniques for solving large linear programs is described. Extensive computational results on the effectiveness of our partitioning procedures and their usefulness for parallel optimization are presented. © 1998 The Mathematical Programming Society, Inc. Published by Elsevier Science B.V.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 23
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 80 (1998), S. 129-160 
    ISSN: 1436-4646
    Keywords: Semidefinite programming ; Infeasible-interior-point method ; Predictor—correctormethod ; Superlinear convergence ; Primal—dual nondegeneracy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract An example of an SDP (semidefinite program) exhibits a substantial difficulty in proving the superlinear convergence of a direct extension of the Mizuno—Todd—Ye type predictor—corrector primal-dual interior-point method for LPs (linear programs) to SDPs, and suggests that we need to force the generated sequence to converge to a solution tangentially to the central path (or trajectory). A Mizuno—Todd—Ye type predictor—corrector infeasible-interior-point algorithm incorporating this additional restriction for monotone SDLCPs (semidefinite linear complementarity problems) enjoys superlinear convergence under strict complementarity and nondegeneracy conditions. © 1998 The Mathematical Programming Society, Inc. Published by Elsevier Science B.V.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 24
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 80 (1998), S. 161-169 
    ISSN: 1436-4646
    Keywords: Variational inequalities ; Complementarity problems ; Walrasian equilibrium ; Computational general equilibrium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract This paper explains a method by which the number of variables in a variational inequality having a certain form can be substantially reduced by changing the set over which the variational inequality is posed. The method applies in particular to certain economic equilibrium problems occurring in applications. We explain and justify the method, and give examples of its application, including a numerical example in which the solution time for the reduced problem was approximately 2% of that for the problem in its original form. © 1998 The Mathematical Programming Society, Inc. Published by Elsevier Science B.V.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 25
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 81 (1998), S. 201-214 
    ISSN: 1436-4646
    Keywords: Integer programming ; Cutting planes ; Cover inequalities ; Lifting ; Gomory mixed integer cuts ; Cut-and-branch
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract We investigate the use of cutting planes for integer programs with general integer variables. We show how cutting planes arising from knapsack inequalities can be generated and lifted as in the case of 0–1 variables. We also explore the use of Gomory's mixed-integer cuts. We address both theoretical and computational issues and show how to embed these cutting planes in a branch-and-bound framework. We compare results obtained by using our cut generation routines in two existing systems with a commercially available branch-and-bound code on a range of test problems arising from practical applications. © 1998 The Mathematical Programming Society, Inc. Published by Elsevier Science B.V.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 26
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 81 (1998), S. 229-256 
    ISSN: 1436-4646
    Keywords: Branch-and-cut algorithm ; Clustering ; Compiler design ; Equipartitioning ; Finite element method ; Graph partitioning ; Layout of electronic circuits ; Separation heuristics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract In this paper we consider the problem ofk-partitioning the nodes of a graph with capacity restrictions on the sum of the node weights in each subset of the partition, and the objective of minimizing the sum of the costs of the edges between the subsets of the partition. Based on a study of valid inequalities, we present a variety of separation heuristics for cycle, cycle with ears, knapsack tree and path-block cycle inequalities among others. The separation heuristics, plus primal heuristics, have been implemented in a branch-and-cut routine using a formulation including variables for the edges with nonzero costs and node partition variables. Results are presented for three classes of problems: equipartitioning problems arising in finite element methods and partitioning problems associated with electronic circuit layout and compiler design. © 1998 The Mathematical Programming Society, Inc. Published by Elsevier Science B.V.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 27
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 81 (1998), S. 327-347 
    ISSN: 1436-4646
    Keywords: Convex composite function ; Second-order global optimality ; Second-order duality ; Variational inequality
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract In recent years second-order sufficient conditions of an isolated local minimizer for convex composite optimization problems have been established. In this paper, second-order optimality conditions are obtained of aglobal minimizer for convex composite problems with a non-finite valued convex function and a twice strictly differentiable function by introducing a generalized representation condition. This result is applied to a minimization problem with a closed convex set constraint which is shown to satisfy the basic constraint qualification. In particular, second-order necessary and sufficient conditions of a solution for a variational inequality problem with convex composite inequality constraints are obtained. © 1998 The Mathematical Programming Society, Inc. Published by Elsevier Science B.V.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 28
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 82 (1998), S. 1-1 
    ISSN: 1436-4646
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 29
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 82 (1998), S. 3-12 
    ISSN: 1436-4646
    Keywords: Symmetric submodular function minimization ; Submodular function minimization ; Symmetric submodular functions ; Submodular functions ; Submodular systems
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract We describe a purely combinatorial algorithm which, given a submodular set functionf on a finite setV, finds a nontrivial subsetA ofV minimizingf[A] + f[V ∖ A]. This algorithm, an extension of the Nagamochi—Ibaraki minimum cut algorithm as simplified by Stoer and Wagner [M. Stoer, F. Wagner, A simple min cut algorithm, Proceedings of the European Symposium on Algorithms ESA '94, LNCS 855, Springer, Berlin, 1994, pp. 141–147] and by Frank [A. Frank, On the edge-connectivity algorithm of Nagamochi and Ibaraki, Laboratoire Artémis, IMAG, Université J. Fourier, Grenbole, 1994], minimizes any symmetric submodular function using O(|V|3) calls to a function value oracle. © 1998 The Mathematical Programming Society, Inc. Published by Elsevier Science B.V.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 30
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 82 (1998), S. 41-81 
    ISSN: 1436-4646
    Keywords: Random sampling ; Greedy algorithm ; Matroid basis ; Matroid partitioning
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract Random sampling is a powerful tool for gathering information about a group by considering only a small part of it. We discuss some broadly applicable paradigms for using random sampling in combinatorial optimization, and demonstrate the effectiveness of these paradigms for two optimization problems on matroids: finding an optimum matroid basis and packing disjoint matroid bases. Application of these ideas to the graphic matroid led to fast algorithms for minimum spanning trees and minimum cuts. An optimum matroid basis is typically found by agreedy algorithm that grows an independent set into an optimum basis one element at a time. This continuous change in the independent set can make it hard to perform the independence tests needed by the greedy algorithm. We simplify matters by using sampling to reduce the problem of finding an optimum matroid basis to the problem of verifying that a givenfixed basis is optimum, showing that the two problems can be solved in roughly the same time. Another application of sampling is to packing matroid bases, also known as matroid partitioning. Sampling reduces the number of bases that must be packed. We combine sampling with a greedy packing strategy that reduces the size of the matroid. Together, these techniques give accelerated packing algorithms. We give particular attention to the problem of packing spanning trees in graphs, which has applications in network reliability analysis. Our results can be seen as generalizing certain results from random graph theory. The techniques have also been effective for other packing problems. © 1998 The Mathematical Programming Society, Inc. Published by Elsevier Science B.V.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 31
    ISSN: 1436-4646
    Keywords: Quadratic assignment ; Special cases ; Polynomially solvable ; Anti-Monge matrices ; Toeplitz matrices
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract This paper investigates a restricted version of the Quadratic Assignment Problem (QAP), where one of the coefficient matrices is an Anti-Monge matrix with non-decreasing rows and columns and the other coefficient matrix is a symmetric Toeplitz matrix. This restricted version is called the Anti-Monge—Toeplitz QAP. There are three well-known combinatorial problems that can be modeled via the Anti-Monge—Toeplitz QAP: (Pl) The “Turbine Problem”, i.e. the assignment of given masses to the vertices of a regular polygon such that the distance of the center of gravity of the resulting system to the center of the polygon is minimized. (P2) The Traveling Salesman Problem on symmetric Monge distance matrices. (P3) The arrangement of data records with given access probabilities in a linear storage medium in order to minimize the average access time. We identify conditions on the Toeplitz matrixB that lead to a simple solution for the Anti-Monge—Toeplitz QAP: The optimal permutation can be given in advance without regarding the numerical values of the data. The resulting theorems generalize and unify several known results on problems (P1), (P2), and (P3). We also show that the Turbine Problem is NP-hard and consequently, that the Anti-Monge—Toeplitz QAP is NP-hard in general. © 1998 The Mathematical Programming Society, Inc. Published by Elsevier Science B.V.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 32
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 85 (1999), S. 135-156 
    ISSN: 1436-4646
    Keywords: Key words: bound constrained quadratic programming – Huber’s M–estimator – condition estimation – Newton iteration – factorization update
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: 1 , the smallest eigenvalue of a symmetric, positive definite matrix, and is solved by Newton iteration with line search. The paper describes the algorithm and its implementation including estimation of λ1, how to get a good starting point for the iteration, and up- and downdating of Cholesky factorization. Results of extensive testing and comparison with other methods for constrained QP are given.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 33
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 85 (1999), S. 35-49 
    ISSN: 1436-4646
    Keywords: Key words: bimatrix game – quasi-strict equilibrium ; Mathematics Subject Classification (1991): 90D05
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 34
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 85 (1999), S. 107-134 
    ISSN: 1436-4646
    Keywords: Key words: equilibrium constraints – variational inequality problems – strong monotonicity – optimality conditions – global convergence ; Mathematics Subject Classification (1991): 90C30, 90C33, 65K05
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 35
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 85 (1999), S. 363-377 
    ISSN: 1436-4646
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: 1 ,...,Am are true, then at least ℓ of the propositions B1,...,Bn are true. The main result of the paper is that the procedure in fact provides a convex hull description.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 36
    ISSN: 1436-4646
    Keywords: Key words: maximum-entropy sampling – branch and bound – nonlinear programming
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 37
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 85 (1999), S. 259-276 
    ISSN: 1436-4646
    Keywords: Key words: linear complementary problems – Q-matrices – polyhedral combinatorics – triangulations of point configurations – 0-1 polytopes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: T (Mx+q)=0, Mx+q≥0, x≥0 has a solution. We explain how one can use the polyhedral structure of the set of all triangulations of a finite point set to determine if an n×n matrix M is a Q-matrix. Our implementation of the algorithm is practical for deciding the Q-nature for all M with n≤8.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 38
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 85 (1999), S. 593-616 
    ISSN: 1436-4646
    Keywords: Key words: concave optimization – conical algorithms –ω-subdivisions Mathematics Subject Classification (1991): 90C26, 65K05
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract. In this paper the problem of finding the global optimum of a concave function over a polytope is considered. A well-known class of algorithms for this problem is the class of conical algorithms. In particular, the conical algorithm based on the so called ω-subdivision strategy is considered. It is proved that, for any given accuracy ε〉0, this algorithm stops in a finite time by returning an ε-optimal solution for the problem, while it is convergent for ε=0.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 39
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 85 (1999), S. 439-467 
    ISSN: 1436-4646
    Keywords: Mathematics Subject Classification (1991): 90C11
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract. We investigate strong inequalities for mixed 0-1 integer programs derived from flow cover inequalities. Flow cover inequalities are usually not facet defining and need to be lifted to obtain stronger inequalities. However, because of the sequential nature of the standard lifting techniques and the complexity of the optimization problems that have to be solved to obtain lifting coefficients, lifting of flow cover inequalities is computationally very demanding. We present a computationally efficient way to lift flow cover inequalities based on sequence independent lifting techniques and give computational results that show the effectiveness of our lifting procedures.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 40
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 85 (1999), S. 525-540 
    ISSN: 1436-4646
    Keywords: Key words: semidefinite programming – perturbation theory – Kantorovi theory – condition number Mathematics Subject Classification (1991): 90C31, 90C25, 90C05
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: theory. This approach also quantifies the size of permissible perturbations. We include a discussion of these results for block diagonal semidefinite programs, of which linear programming is a special case.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 41
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 86 (1999), S. 219-223 
    ISSN: 1436-4646
    Keywords: Key words: linear programming – computational complexity – complexity measure Mathematics Subject Classification (1991): 90C05, 90C60, 68Q25
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract. Given an m×n integer matrix A of full row rank, we consider the problem of computing the maximum of ∥B -1 A∥2 where B varies over all bases of A. This quantity appears in various places in the mathematical programming literature. More recently, logarithm of this number was the determining factor in the complexity bound of Vavasis and Ye’s primal-dual interior-point algorithm. We prove that the problem of approximating this maximum norm, even within an exponential (in the dimension of A) factor, is NP-hard. Our proof is based on a closely related result of L. Khachiyan [1].
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 42
    ISSN: 1436-4646
    Keywords: Key words: non-interior point method – complementarity problem – smoothing function – homotopy method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract. We propose a class of non-interior point algorithms for solving the complementarity problems(CP): Find a nonnegative pair (x,y)∈ℝ 2n satisfying y=f(x) and x i y i =0 for every i∈{1,2,...,n}, where f is a continuous mapping from ℝ n to ℝ n . The algorithms are based on the Chen-Harker-Kanzow-Smale smoothing functions for the CP, and have the following features; (a) it traces a trajectory in ℝ 3n which consists of solutions of a family of systems of equations with a parameter, (b) it can be started from an arbitrary (not necessarily positive) point in ℝ 2n in contrast to most of interior-point methods, and (c) its global convergence is ensured for a class of problems including (not strongly) monotone complementarity problems having a feasible interior point. To construct the algorithms, we give a homotopy and show the existence of a trajectory leading to a solution under a relatively mild condition, and propose a class of algorithms involving suitable neighborhoods of the trajectory. We also give a sufficient condition on the neighborhoods for global convergence and two examples satisfying it.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 43
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 86 (1999), S. 41-50 
    ISSN: 1436-4646
    Keywords: Key words: resolvent method – proximal point method – bundle method – bundle-trust region method – subgradient Mathematics Subject Classification (1991): 90C25, 49M45
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract. This paper establishes a linear convergence rate for a class of epsilon-subgradient descent methods for minimizing certain convex functions on ℝ n . Currently prominent methods belonging to this class include the resolvent (proximal point) method and the bundle method in proximal form (considered as a sequence of serious steps). Other methods, such as a variant of the proximal point method given by Correa and Lemaréchal, can also fit within this framework, depending on how they are implemented. The convex functions covered by the analysis are those whose conjugates have subdifferentials that are locally upper Lipschitzian at the origin, a property generalizing classical regularity conditions.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 44
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 86 (1999), S. 387-415 
    ISSN: 1436-4646
    Keywords: Key words: semi-infinite optimization – reduction approach – stationary point – strong stability – extended Mangasarian-Fromovitz constraint qualification Mathematics Subject Classification (1991): 90C30, 90C31, 90C34, 49M39
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract. The paper deals with semi-infinite optimization problems which are defined by finitely many equality constraints and infinitely many inequality constraints. We generalize the concept of strongly stable stationary points which was introduced by Kojima for finite problems; it refers to the local existence and uniqueness of a stationary point for each sufficiently small perturbed problem, where perturbations up to second order are allowed. Under the extended Mangasarian-Fromovitz constraint qualification we present equivalent conditions for the strong stability of a considered stationary point in terms of first and second derivatives of the involved functions. In particular, we discuss the case where the reduction approach is not satisfied.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 45
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 86 (1999), S. 313-334 
    ISSN: 1436-4646
    Keywords: Key words: linear programming – potential functions – infeasible-interior-point methods – homogeneity – self-dual
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 46
    ISSN: 1436-4646
    Keywords: Key words: basis recovery – partition – principal pivot transforms – Balinski-Tucker tableaus – quadratic programming – linear complementarity problems – interior point methods – sufficient matrices – crossover – Criss-Cross method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract. Optimal solutions of interior point algorithms for linear and quadratic programming and linear complementarity problems provide maximally complementary solutions. Maximally complementary solutions can be characterized by optimal partitions. On the other hand, the solutions provided by simplex–based pivot algorithms are given in terms of complementary bases. A basis identification algorithm is an algorithm which generates a complementary basis, starting from any complementary solution. A partition identification algorithm is an algorithm which generates a maximally complementary solution (and its corresponding partition), starting from any complementary solution. In linear programming such algorithms were respectively proposed by Megiddo in 1991 and Balinski and Tucker in 1969. In this paper we will present identification algorithms for quadratic programming and linear complementarity problems with sufficient matrices. The presented algorithms are based on the principal pivot transform and the orthogonality property of basis tableaus.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 47
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 86 (1999), S. 417-431 
    ISSN: 1436-4646
    Keywords: Mathematics Subject Classification (1991): 90A11, 90B50, 90C90, 90D65
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract. We study the following decision-making scenario: A linear program is solved by a set of agents arranged hierarchically in a tree, where each agent decides the level of certain variables, and has a distinct objective function, known to all agents. Authority is reflected in two ways: Agents higher in the tree set their variables first; and agents that are siblings in the tree resolve their game by focusing on the Nash equilibrium that is optimum for the agent above them. We give a necessary and sufficient condition for such a hierarchy to be efficient (i.e., to have perfect coordination, to ultimately optimize the objective of the firm). We study problems related to designing a hierarchy (assigning decision makers to positions in the tree) in order to achieve efficiency or otherwise optimize coordination.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 48
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 86 (1999), S. 533-563 
    ISSN: 1436-4646
    Keywords: Key words: generalized linear complementarity problem – non-interior continuation method – Newton method – Q-quadratical convergence Mathematics Subject Classification (1991): 90C33
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract. In this paper, we propose a non-interior continuation method for solving generalized linear complementarity problems (GLCP) introduced by Cottle and Dantzig. The method is based on a smoothing function derived from the exponential penalty function first introduced by Kort and Bertsekas for constrained minimization. This smoothing function can also be viewed as a natural extension of Chen-Mangasarian’s neural network smooth function. By using the smoothing function, we approximate GLCP as a family of parameterized smooth equations. An algorithm is presented to follow the smoothing path. Under suitable assumptions, it is shown that the algorithm is globally convergent and local Q-quadratically convergent. Few preliminary numerical results are also reported.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 49
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 86 (1999), S. 463-473 
    ISSN: 1436-4646
    Keywords: Key words: semidefinite relaxations – quadratic programming Mathematics Subject Classification (1991): 20E28, 20G40, 20C20
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract. We demonstrate that if A 1,...,A m are symmetric positive semidefinite n×n matrices with positive definite sum and A is an arbitrary symmetric n×n matrix, then the relative accuracy, in terms of the optimal value, of the semidefinite relaxation $$\max_X\{\Tr(AX)\mid\, \Tr(A_iX)\le1,\,\,i=1,...,m;\,X\succeq0\} \eqno{\hbox{(SDP)}}$$ of the optimization program $$x^TAx\to\max\mid\, x^TA_ix\le 1,\,\,i=1,...,m \eqno{\hbox{(P)}}$$ is not worse than $$1-\frac{1}{{2\ln(2m^2)}}$$ . It is shown that this bound is sharp in order, as far as the dependence on m is concerned, and that a~feasible solution x to (P) with $$x^TAx\ge \frac{{\Opt(\hbox{{\rm SDP}})}}{{2\ln(2m^2)}} \eqno{(*)}$$ can be found efficiently. This somehow improves one of the results of Nesterov [4] where bound similar to (*) is established for the case when all Ai are of rank 1.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 50
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 86 (1999), S. 161-185 
    ISSN: 1436-4646
    Keywords: Mathematics Subject Classification (1991): 90C10
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract. This paper considers the precedence constrained knapsack problem. More specifically, we are interested in classes of valid inequalities which are facet-defining for the precedence constrained knapsack polytope. We study the complexity of obtaining these facets using the standard sequential lifting procedure. Applying this procedure requires solving a combinatorial problem. For valid inequalities arising from minimal induced covers, we identify a class of lifting coefficients for which this problem can be solved in polynomial time, by using a supermodular function, and for which the values of the lifting coefficients have a combinatorial interpretation. For the remaining lifting coefficients it is shown that this optimization problem is strongly NP-hard. The same lifting procedure can be applied to (1,k)-configurations, although in this case, the same combinatorial interpretation no longer applies. We also consider K-covers, to which the same procedure need not apply in general. We show that facets of the polytope can still be generated using a similar lifting technique. For tree knapsack problems, we observe that all lifting coefficients can be obtained in polynomial time. Computational experiments indicate that these facets significantly strengthen the LP-relaxation.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 51
    Electronic Resource
    Electronic Resource
    Springer
    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
    Topics: Computer Science , Mathematics
    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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 52
    Electronic Resource
    Electronic Resource
    Springer
    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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 53
    Electronic Resource
    Electronic Resource
    Springer
    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
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 54
    Electronic Resource
    Electronic Resource
    Springer
    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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 55
    Electronic Resource
    Electronic Resource
    Springer
    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
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 56
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 71 (1995), S. 17-28 
    ISSN: 1436-4646
    Keywords: Descent method ; Proximal algorithm ; Direction-finding subproblem
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 57
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 71 (1995), S. 51-69 
    ISSN: 1436-4646
    Keywords: Smoothing ; Convex inequalities ; Linear complementarity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract A smooth approximationp (x, α) to the plus function max{x, 0} is obtained by integrating the sigmoid function 1/(1 + e−αx ), commonly used in neural networks. By means of this approximation, linear and convex inequalities are converted into smooth, convex unconstrained minimization problems, the solution of which approximates the solution of the original problem to a high degree of accuracy forα sufficiently large. In the special case when a Slater constraint qualification is satisfied, an exact solution can be obtained for finiteα. Speedup over MINOS 5.4 was as high as 1142 times for linear inequalities of size 2000 × 1000, and 580 times for convex inequalities with 400 variables. Linear complementarity problems are converted into a system of smooth nonlinear equations and are solved by a quadratically convergent Newton method. For monotone LCPs with as many as 10 000 variables, the proposed approach was as much as 63 times faster than Lemke's method.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 58
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 71 (1995), S. 127-136 
    ISSN: 1436-4646
    Keywords: Parametric optimization ; Mixed-integer program ; Value functions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract We identify a class of formulas computable in polynomial time such that the functions defined by these formulas are precisely the value functions of mixed-integer programs with rational constraint coefficients.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 59
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 71 (1995), S. 137-151 
    ISSN: 1436-4646
    Keywords: Quadratic assignment problem ; Lower bounds
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract We consider transformations of the (metric) Quadratic Assignment Problem (QAP) that exploit the metric structure of a given instance. We show in particular how the structural properties of rectangular grids can be used to improve a given lower bound. Our work is motivated by previous research of Palubetskes (1988), and it extends a bounding approach proposed by Chakrapani and Skorin-Kapov (1993). Our computational results indicate that the present approach is practical; it has been applied to problems of dimension up ton = 150. Moreover, the new approach yields by far the best lower bounds on most of the instances of metric QAPs that we considered.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 60
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 71 (1995), S. 207-219 
    ISSN: 1436-4646
    Keywords: Subgradient optimization ; Relaxation methods ; Projection methods
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 61
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 71 (1995), S. 221-245 
    ISSN: 1436-4646
    Keywords: Linear programming ; Presolving ; Interior-point methods
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 62
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 80 (1998), S. 125-125 
    ISSN: 1436-4646
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 63
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 80 (1998), S. 91-123 
    ISSN: 1436-4646
    Keywords: Complexity of linear programming ; Interior point methods ; Conditioning ; Error analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract In this paper we study the complexity of solving linear programs in finite precision arithmetic. This is the normal setup in scientific computation, as digital computers work in finite precision. We analyze two aspects of the complexity: one is the number of arithmetic operations required to solve the problem approximately, and the other is the working precision required to carry out some critical computations safely. We show how the “conditioning” of the problem instance affects the working precision required and the computational requirements of a classical logarithmic barrier algorithm to approximate the optimal value of the problem within a given tolerance. Our results show that these complexity measures depend linearly on the logarithm of a certain condition measure. We carry out the analysis by looking at how well Newton's Method can follow the central trajectory of the feasible set, and computing error bounds in terms of the condition measure. These results can be interpreted as a theoretical indication of “good” numerical behavior of the logarithmic barrier method, in the sense that a problem instance “twice as hard” as the other from the numerical point of view, requires only at most twice as much precision to be solved. © 1998 The Mathematical Programming Society, Inc. Published by Elsevier Science B.V.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 64
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical programming 80 (1998), S. 213-237 
    ISSN: 1436-4646
    Keywords: Maximum satisfiability ; Horn clauses ; Directed hypergraphs ; Minimum cut ; Generalized set covering
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract In this paper we consider the Maximum Horn Satisfiability problem, which is reduced to the problem of finding a minimum cardinality cut on a directed hypergraph. For the latter problem, we propose different IP formulations, related to three different definitions of hyperpath weight. We investigate the properties of their linear relaxations, showing that they define a hierarchy. The weakest relaxation is shown to be equivalent to the relaxation of a well known IP formulation of Max Horn SAT, and to a max-flow problem on hypergraphs. The tightest relaxation, which is a disjunctive programming problem, is shown to have integer optimum. The intermediate relaxation consists in a set covering problem with a possible exponential number of constraints. This latter relaxation provides an approximation of the convex hull of the integer solutions which, as proven by the experimental results given, is much tighter than the one known in the literature. © 1998 The Mathematical Programming Society, Inc. Published by Elsevier Science B.V.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 65
    Electronic Resource
    Electronic Resource
    Springer
    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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 66
    Electronic Resource
    Electronic Resource
    Springer
    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
    Topics: Computer Science
    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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 67
    Electronic Resource
    Electronic Resource
    Springer
    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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 68
    Electronic Resource
    Electronic Resource
    Springer
    Computing 54 (1995), S. 331-346 
    ISSN: 1436-5057
    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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 69
    Electronic Resource
    Electronic Resource
    Springer
    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
    Topics: Computer Science
    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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 70
    Electronic Resource
    Electronic Resource
    Springer
    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).
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 71
    Electronic Resource
    Electronic Resource
    Springer
    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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 72
    Electronic Resource
    Electronic Resource
    Springer
    Computing 55 (1995), S. 43-53 
    ISSN: 1436-5057
    Keywords: Interval analysis ; range computation ; inclusion monotonicity ; Bernstein coefficients
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    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).
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 73
    Electronic Resource
    Electronic Resource
    Springer
    Computing 55 (1995), S. 1-22 
    ISSN: 1436-5057
    Keywords: 65L ; 34C ; Reversible integration ; symplectic integrators ; variable step size ; long time integration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    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).
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 74
    Electronic Resource
    Electronic Resource
    Springer
    Computing 55 (1995), S. 91-111 
    ISSN: 1436-5057
    Keywords: 65F15 (47A56) ; Nonlinear eigenvalue problem ; numerical solution ; condition number
    Source: Springer Online Journal Archives 1860-2000
    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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 75
    Electronic Resource
    Electronic Resource
    Springer
    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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 76
    Electronic Resource
    Electronic Resource
    Springer
    Computing 55 (1995), S. 75-89 
    ISSN: 1436-5057
    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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 77
    Electronic Resource
    Electronic Resource
    Springer
    Computing 55 (1995), S. 163-180 
    ISSN: 1436-5057
    Keywords: 65L05 ; Hopf bifurcation ; Runge-Kutta ; Poincare map
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 78
    Electronic Resource
    Electronic Resource
    Springer
    Computing 55 (1995), S. 181-189 
    ISSN: 1436-5057
    Keywords: 65N55 ; 65F10 ; Smoothing property ; multi-grid method ; semi-iteration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 79
    Electronic Resource
    Electronic Resource
    Springer
    Computing 55 (1995), S. 207-221 
    ISSN: 1436-5057
    Keywords: 65COS ; 65DIS ; Particle methods ; discrepancy estimates ; nonlinear functionals
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 80
    Electronic Resource
    Electronic Resource
    Springer
    Computing 55 (1995), S. 223-236 
    ISSN: 1436-5057
    Keywords: 65L05 ; 65L06 ; Runge-Kutta methods ; interpolations ; delay differential equations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 81
    Electronic Resource
    Electronic Resource
    Springer
    Computing 55 (1995), S. I 
    ISSN: 1436-5057
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 82
    Electronic Resource
    Electronic Resource
    Springer
    Computing 55 (1995), S. 237-253 
    ISSN: 1436-5057
    Keywords: 65N06 ; Finite difference method ; impulsive partial differential-functional equations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 83
    Electronic Resource
    Electronic Resource
    Springer
    Computing 55 (1995), S. 191-206 
    ISSN: 1436-5057
    Keywords: 68Q25 ; 68U05 ; Rectangles ; balanced cuts ; separation ; binary space partition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 84
    Electronic Resource
    Electronic Resource
    Springer
    Computing 55 (1995), S. 271-288 
    ISSN: 1436-5057
    Keywords: 65F10 ; Finite elements ; multigrid methods ; error control
    Source: Springer Online Journal Archives 1860-2000
    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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 85
    Electronic Resource
    Electronic Resource
    Springer
    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.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 86
    Electronic Resource
    Electronic Resource
    Springer
    Computing 56 (1996), S. 29-46 
    ISSN: 1436-5057
    Keywords: 94A15 ; Optimal and heuristic encoding ; shortest paths ; textual substitution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Es werden Text-Komprimierungsprobleme behandelt, bei denen Teilworte durch Codeworte ersetzt werden, sodaß der ursprüngliche Text durch eine kürzere Codesequenz repräsentiert wird. Das geschieht mit Hilfe eines statischen Wörterbuchs. Wir führen eine neue effiziente on-line Heuristik ein, welche die lokale Komprimierungsrate maximiert. Von diesem fractional greedy Verfahren wird das Verhalten im schlechtesten Fall für verschiedene Typen von Wörterbüchern untersucht.
    Notes: Abstract Text-compression problems are considered where substrings are substitued by code-words according to a static dictionary such that the original text is encoded by a shorter code sequence. We introduce a new efficient on-line heuristic which locally maximizes the compaction ratio. The worst-case behaviour of this fractional greedy heuristic is investigated for several types of dictionaries.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 87
    ISSN: 1436-5057
    Keywords: 65 L 05 ; Rosenbrock-type methods ; quasilinear-implicit differential equations ; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Bei der Lösung quasilinear-impliziter ODEs mittels Rosenbrock-Typ-Methoden können trotz guter Stabilitätseigenschaften (A- bzw. L-Stabilität) des Grundverfahrens Stabilitätsprobleme auftreten. Diese Schwierigkeiten sind auf Ungenauigkeiten bei der Berechnung künstlich eingeführter Komponenten (Überführung in DAEs) zurückzuführen. Die Arbeit untersucht die Ursachen für diese Effekte und zeigt Möglichkeiten, diese zu überwinden.
    Notes: Abstract The solution of quasilinear-implicit ODEs using Rosenbrock type methods may suffer from stability problems despite stability properties such as A-stability or L-stability, respectively. These problems are caused by inexact computation of artificial introduced components (transformation to DAE system). The paper investigates the source of the numerical difficulties and shows modifications to overcome them.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 88
    Electronic Resource
    Electronic Resource
    Springer
    Computing 56 (1996), S. 61-85 
    ISSN: 1436-5057
    Keywords: 65N55 ; 65N38 ; Boundary integral equations ; domain decomposition ; Schwarz methods
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Es werden zwei Gebietszerlegungsalgorithmen für die numerische Behandlung von Randintegralgleichungen der ersten Art untersucht. Die Verfahren beruhen auf derh-Version der Galerkinmethode für Randelemente, auf die die multiplikative und die additive Schwarz-Methode angewandt werden. Für zweidimensionale Probleme wird gezeigt, daß die Konvergenzraten beider Methoden unabhängig von der Anzahl der Unbekannten sind. Numerische Resultate für einfache zweidimensionale und dreidimensionale Modellprobleme, die von der Laplace-Gleichung mit Dirichlet oder Neumann-Randbedingungen stammen, werden diskutiert. Eine Gebietszerlegungsstrategie für den Fall vieler Teilgebiete wird anhand eines dreidimensionalen Schirmproblems demonstriert.
    Notes: Abstract This paper investigates two domain decomposition algorithms for the numerical solution of boundary integral equations of the first kind. The schemes are based on theh-type boundary element Galerkin method to which the multiplicative and the additive Schwarz methods are applied. As for twodimensional problems, the rates of convergence of both methods are shown to be independent of the number of unknowns. Numerical results for standard model problems arising from Laplaces' equation with Dirichlet or Neumann boundary conditions in both two and three dimensions are discussed. A multidomain decomposition strategy is indicated by means of a screen problem in three dimensions, so as to obtain satisfactory experimental convergence rates.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 89
    Electronic Resource
    Electronic Resource
    Springer
    Computing 56 (1996), S. 1-27 
    ISSN: 1436-5057
    Keywords: 65F10 ; 65H10 ; 65N22 ; 65N30 ; 65N55 ; Semiconductor device ; drift-diffusion equations ; finite element methods ; Gummel's method ; preconditioned conjugate gradient methods ; Schur complement ; domain decomposition massively parallel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Diese Arbeit enthält die Beschreibung, Analyse und Implementierung eines parallelen iterativen Verfahrens zur Lösung der stationären Drift-Diffusions-Gleichung für ein zweidimensionales Halbleitermodell. Die Unbekannten unseres Modells sind das elektrostatische Potential und die Quasi-Fermi-Potentiale der Elektronen und Löcher. Unsere Diskretisierung verwendet die Finite-Element-Methode mit ‘mass limping’ für das elektrostatische Potential und hybride Elemente mit lokaler Stromerhaltung für die Kontinuitätsgleichung. Zur Lösung der entsprechenden nichtlinearen Gleichungen wird eine Version des Gummel-Algorithmus verwendet, der lediglich die Lösung positiv definiter, symmetrischer linearer Gleichungssysteme erfordert. Wir zeigen, daß diese Methode eine Konvergenzrate besitzt, die nur logarithmisch von der Schrittweite abhängt. Die (inneren) nichtlinearen Löser der elektrostatischen Potentialgleichung konvergieren gitterunabhängig quadratisch. Wir beschreiben auch eine Implementierung auf einem MasPar MP-1-Parallelrechner, wobei die auftretenden linearen Systeme mit einem vorkonditionierten cg-Verfahren approximiert werden. Gebietszerlegungsmethoden werden eingesetzt, um die notwendige Matrix-Vektor-Multiplikation zu parallelisieren und Vorkonditionierer dieser schlechtkonditionierten Systeme zu erstellen. Die vorkonditionierten linearen Löser haben ebenfalls eine Konvergenzrate, die logarithmisch vom Verhältnis Teilgebietsgröße zu Schrittweite abhängt und welche robust ist bezüglich stark variierenden Koeffizientenfunktionen des zugrundeliegenden elliptischen Operators. Experimente auf einem Parallelrechner werden diskutiert.
    Notes: Abstract In this paper we describe, analyse and implement a parallel iterative method for the solution of the steady-state drift diffusion equations governing the behaviour of a semiconductor device in two space dimensions. The unknowns in our model are the electrostatic potential and the electron and hole quasi-Fermi potentials. Our discretisation consists of a finite element method with mass lumping for the electrostatic potential equation and a hybrid finite element with local current conservation properties for the continuity equations. A version of Gummel's decoupling algorithm which only requires the solution of positive definite symmetric linear systems is used to solve the resulting nonlinear equations. We show that this method has an overall rate of convergence which only degrades logarithmically as the mesh is refined. Indeed the (inner) nonlinear solves of the electrostatic potential equation converge quadratically, with a mesh independent asymptotic constant. We also describe an implementation on a MasPar MP-1 data parallel machine, where the required linear systems are solved by the preconditioned conjugate gradient method. Domain decomposition methods are used to parallelise the required matrix-vector multiplications and to build preconditioners for these very poorly-conditioned systems. Our preconditioned linear solves also have a rate of convergence which degrades logarithmically as the grid is refined relative to subdomain size, and their performance is resilient to the severe layers which arise in the coefficients of the underlying elliptic operators. Parallel experiments are given.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 90
    Electronic Resource
    Electronic Resource
    Springer
    Computing 56 (1996), S. 87-93 
    ISSN: 1436-5057
    Keywords: 41A15 ; 65D30 ; Integration formulas ; iterated cubic splines
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Wir erarbeiten eine Anwendung iterativer kubischer Splines auf die numerische Integrationsformeln. Wir geben einige numerische Beispiele, um den Nutzen unserer Methoden zu illustrieren.
    Notes: Abstract We consider an application of iterated cubic splines to numerical integration formulas. Some numerical examples are given to illustrate usefulness of our methods.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 91
    Electronic Resource
    Electronic Resource
    Springer
    Computing 56 (1996), S. 95-104 
    ISSN: 1436-5057
    Keywords: 68M20 ; Probabilistic algorithm ; online scheduling ; interval ; busy time
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Wir betrachten das Problem der Zuteilung von Aufgaben bestimmter Rechenzeit auf einem Rechner, um so seine Auslastung zu maximieren. Die Aufgabe besteht darin, einen probabilistischen Online-Algorithmus mit vernünftigem worst-case Performance-Verhältnis zu finden. Wir geben die Antwort auf ein offenes Problem von Lipton und Tompkins, das das bestmögliche Verhältnis betrifft. Weiter verallgemeinern wir ihre Ergebnisse auf einm-Maschinen-Analogon. Schließlich wird eine Variante des Problems analysiert, in dem der Rechner mit einem Zwischenspeicher für einen Job versehen ist.
    Notes: Abstract We consider the problem of scheduling tasks requiring certain processing times on one machine so that the busy time of the machine is maximized. The problem is to find a probabilistic online algorithm with reasonable worst case performance ratio. We answer an open problem of Lipton and Tompkins concerning the best possible ratio that can be achieved. Furthermore, we extend their results to anm-machine analogue. Finally, a variant of the problem is analyzed, in which the machine is provided with a buffer to store one job.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 92
    Electronic Resource
    Electronic Resource
    Springer
    Computing 56 (1996), S. 105-116 
    ISSN: 1436-5057
    Keywords: 65C10 ; 62M99 ; 62F03 ; Pseudo-random number generators ; statistical evaluation ; tests ; error of type II ; renewal process
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung In einem früheren Artikel, vgl. [7], hat die erste Autorin Bewertungsmethoden von Pseudozufallsgeneratoren entwickelt, die auf Ideen der Computer-Simulation basieren. Dabei werden die Pseudozufallszahlen des getesteten Generators zur Modellierung gewisser Verteilungen herangezogen. Diese kann man mit theoretischen Verteilungen oder mit Verteilungen, die mittels wohlbekannter kanonischer Generatoren modelliert werden, vergleichen. Obige Methode kann aber versagen, falls wesentlich verschiedene Generatoren die Simulationen ausführen, welche mit Hilfe unserer einfachen Tests nicht auseinandergehalten werden können. In diesem Artikel werden Typen von kritischen Verteilungen konstruiert, die geometrisch bzw. arithmetisch gennant werden und durch bestimmte Bedingungen dargestellt werden. Es wird darauf hingewiesen, wie die Teilintervall-Methode, welche von den in [7] eingeführten Tests hergeleitet wird, zur Aufdeckung der kritischen Verteilungstype angewendet werden kann. In zusätczlichen Bemerkungen werden noch weitere Anwendungsaspekte unserer Bewertungsmethode betrachtet.
    Notes: Abstract In an earlier paper, cf. [7], the first author developed methods for evaluation of pseudo-random number generators based on ideas of computer simulation. More precisely, pseudo-random numbers of the tested generator are used to model certain distributions which can be compared with theoretical ones or with distributions modeled by means of well-known canonical generators. But this method can fail if essentially different generators produce simulations that cannot be distinguished by means of simple statistical tests developed in [7]. In the present paper two critical types of distributions, named geometric and arthmetic, are constructed that illustrate the circumstances above. Also it is shown how the subinterval method derived from the tests in [7] can serve to detect the described critical types of distributions. Additional aspects of old and new methods are shortly discussed.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 93
    Electronic Resource
    Electronic Resource
    Springer
    Computing 56 (1996), S. 117-139 
    ISSN: 1436-5057
    Keywords: 65N22 ; 65N50 ; Local defect correction ; fast adaptive composite grid method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Wir analysieren einen Spezialfall der lokalen Defektkorrektur-Methode (LDC) die in [4] eingeführt wurde. Wir beschränken uns auf Finite-Differenzen-Diskretisierungen elliptischer Randwertprobleme. Die lokale Defektkorrektur-Methode verwendet Diskretisierungen auf einem globalen uniformen groben Gitter und einem oder mehreren lokalen uniformen feinen Gittern zur Approximation der stetigen Lösung. Wir beweisen, daß diese LDC-Methode als iterative Methode zur Lösung einer zugehörigen Diskretisierung auf dem zusammengesetzten Gitter betrachtet werden kann. Dieses Resultat ermöglicht es, wichtige Eigenschaften der LDC-Methode zu erklären, z.B. in Bezug auf die Größenordnung des Diskretisierungsfehlers. Außerdem ermöglicht die Formulierung der LDC-Methode als iterativer Solver für ein gegebenes Problem auf dem zusammengesetzten Gitter den Beweis eines engen Zusammenhangs zwischen LDC und der “Fast adaptive grid (FAC)”-Methode aus [8–10].
    Notes: Abstract We analyze a special case of the Local Defect Correction (LDC) method introduced in [4]. We restrict ourselves to finite difference discretizations of elliptic boundary value problems. The LDC method uses the discretization on a uniform global coarse grid and on one or more uniform local fine grids for approximating the continuous solution. We prove that this LDC method can be seen as an iterative method for solving an underlying composite grid discretization. This result makes it possible to explain important properties of the LDC method, e.g. concerning the size of the discretization error. Furthermore, the formulation of LDC as an iterative solver for a given composite grid problem makes it possible to prove a close correspondence between LDC and the Fast Adaptive Composite grid (FAC) method from [8–10].
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 94
    Electronic Resource
    Electronic Resource
    Springer
    Computing 56 (1996), S. 165-172 
    ISSN: 1436-5057
    Keywords: 90B35 ; 90C27 ; Combinatorial problems ; bin packing ; online algorithm ; worst-case analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Wir analysieren den von Kinnersley und Langston [5] vorgeschlagenen FFH-Algorithmus. Wir zeigen, daß der FFH Algorithmus eine scharfe Worst-Case Schranke von 1.7 hat und beantworten damit eine Frage in [5]. Variable Bingrößen werden ebenfalls betrachtet.
    Notes: Abstract We investigate and analyze the FFH algorithm proposed by Kinnersley and Langston [5]. We prove that the tight worst-case performance bound of FFH algorithm is 1.7, thereby answering a question in [5]. The case that bin sizes can be chosen is also considered.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 95
    Electronic Resource
    Electronic Resource
    Springer
    Computing 56 (1996), S. 237-258 
    ISSN: 1436-5057
    Keywords: 65N55 ; 65N30 ; 65N22 ; 65N38 ; 78A30 ; Nonlinear partial differential equations ; domain decomposition ; boundary element methods ; finite element methods ; coupling ; magnetic field calculations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung In der vorliegenden Arbeit wird ein effizienter paralleler Algorithmus zur Lösung linearer und nichtlinearer Außenraumprobleme, wie sie z.B. in der Magnetostatik auftreten, beschrieben. Er basiert auf der Kopplung der Finite Elemente Methode mit der Galerkin-Randelementmethode mit Hilfe von Gebietszerlegungstechniken über eine einheitliche Variationsformulierung. Auf diese Weise können z.B. Magnetfeldprobleme mit der Sommerfeldschen Abstrahlbedingung vollständig modelliert werden. Die durch die Galerkin-Randelementmethode entstehende nichtsymmetrische Matrix wird in eine symmetrische indefinite Matrix transformiert, um Bramble/Pasciak's CG-Verfahren für indefinite Systeme anzuwenden. Zur Vorkonditionierung werden die neuesten Resultate auf dem Gebiet der Gebietszerlegungsmethoden genutzt. Numerische Resultate, die für zwei praktisch interessante Probleme, darunter ein nichtlineares, auf einem Mehrprozessorsystem erhalten wurden, werden diskutiert.
    Notes: Abstract An efficient parallel algorithm for solving linear and nonlinear exterior boundary value problems arising, e.g., in magnetostatics is presented. It is based upon the domaindecomposition-(DD)-coupling of Finite Element and Galerkin Boundary Element Methods which results in a unified variational formulation. In this way, e.g., magnetic field problems in an unbounded domain with Sommerfeld's radiation condition can be modelled correctly. The problem of a nonsymmetric system matrix due to Galerkin-BEM is overcome by transforming it into a symmetric but indefinite matrix and applying Bramble/Pasciak's CG for indefinite systems. For preconditioning, the main ideas of recent DD research are being applied. Test computations on a multiprocessor system were performed for two problems of practical interest including a nonlinear example.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 96
    Electronic Resource
    Electronic Resource
    Springer
    Computing 56 (1996), S. 303-322 
    ISSN: 1436-5057
    Keywords: 65N20 ; 65N30 ; 65N55 ; Multigrid ; elliptic problems ; anisotropy ; convection-dominated
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Wir betrachten eine Zweigittermethode, die auf der Approximation des Schurkomplements basiert. Wir untersuchen die Abhängigkeit der Zweigitter-Konvergenzrate von bestimmten Parametern des Problems. Als Testprobleme wählen wir die rotierte anisotrope Diffusionsgleichung und die Konvektions-Diffusions-Gleichung. Mittels Fourieranalyse zeigen wir, daß die Zweigittermethode robust bezüglich Variationen in den relevanten Parametern des Problems ist. Als Mehrgittermethode verwenden wir einen üblichenW-Zyklus auf groben Gittern. Diese Mehrgittermethode hat dann dieselbe algorithmische Struktur wie eine Standard-Mehrgittermethode und ist effizient. Weiters erhalten wir bei Anwendung auf die zwei Testprobleme ebenso wie für die Zweigittermethode starke Robustheit bezüglich Variation der Problemparameter.
    Notes: Abstract We consider a two-grid method based on approximation of the Schur complement. We study the dependence of the two-grid convergence rate on certain problem parameters. As test problems we take the rotated anisotropic diffusion equation and the convection-diffusion equation. Using Fourier analysis we show that for both test problems the two-grid method is robust w.r.t. variation in the relevant problem parameters. For the multigrid method we use a standardW-cycle on coarse grids. This multigrid method then has the same algorithmic structure as a standard multigrid method and is fairly efficient. Moreover, when applied to the two test problems then, as in the two-grid method, we have a strong robustness w.r.t. variation of the problem parameters.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 97
    Electronic Resource
    Electronic Resource
    Springer
    Computing 56 (1996), S. 259-301 
    ISSN: 1436-5057
    Keywords: 15A12 ; 35Q30 ; 65N30 ; 41A17 ; 41A63 ; Saddle point problems ; LBB condition ; multiresolution analysis ; wavelets ; time dependent problems ; Schur complements ; preconditioning
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung In dieser Arbeit werden Galerkin-Verfahren für das Stokes-Problem untersucht, die auf speziell angepaßten Multiresolution-Ansätzen beruhen. Insbesondere wird gezeigt, daß gewisse Konstruktionsprinzipien für Wavelets auf gleichförmigen Gittern für jede Raumdimension und beliebige gewünschte Exaktheitsordnung auf Parre von Ansatzräumen führen, die die Ladyšenskaja-Babuška-Brezzi-Bedingung erfüllen. Darüber hinaus ergeben sich auch im instationären Fall aus den entsprechenden stabilen Multiskalenzerlegungen effiziente Vorkonditionierer für die Schurkomplemente entsprechenden systemmatrizen. Die Ergebnisse werden anhand einiger konkreter Realisierungen und numerischer Tests illustriert.
    Notes: Abstract The purpose of this paper is to investigate Galerkin schemes for the Stokes equations based on a suitably adapted multiresolution analysis. In particular, it will be shown that techniques developed in connection with shift-invariant refinable spaces give rise to trial spaces of any desired degree of accuracy satisfying the Ladyšenskaja-Babuška-Brezzi condition for any spatial dimension. Moreover, in the time dependent case efficient preconditioners for the Schur complements of the discrete systems of equations can be based on corresponding stable multiscale decompositions. The results are illustrated by some concrete examples of adapted wavelets and corresponding numerical experiments.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 98
    Electronic Resource
    Electronic Resource
    Springer
    Computing 56 (1996), S. 323-341 
    ISSN: 1436-5057
    Keywords: 65D05 ; 65D07 ; 65D10 ; Piece wise Hermite interpolation ; shape preserving
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Ein lokaler Ansatz zur stückweisenC 1-Hermite-Interpolation wird vorgestellt. Die Interpolierende besteht aus zusammengesetzten kubischen und quadratischen Segmenten; sie erhält die Monotonie und/oder die Konvexität der Daten. Unter geeigneten Voraussetzungen approximier sie von vierter Ordnung.
    Notes: Abstract A local scheme for piecewiseC 1-Hermite interpolation is presented. The interpolant is obtained patching together cubic with quadratic polynomial segments; it is co-monotone and/or co-convex with the data. Under appropriate assumptions the method is fourth-order accurate.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 99
    Electronic Resource
    Electronic Resource
    Springer
    Computing 56 (1996), S. 371-383 
    ISSN: 1436-5057
    Keywords: 65M10 ; Stability ; MacCormack scheme ; advection equation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Wir betrachten die zweidimensionale skalare Advektionsgleichung $$\frac{{\partial u}}{{\partial t}} = \hat a\frac{{\partial u}}{{\partial x}} + \hat b\frac{{\partial u}}{{\partial y}}$$ und zeigen, daß der Stabilitätsbereich des MacCormack-Schemasgenau durch $$\left( {\hat a\frac{{\Delta _t }}{{\Delta _x }}} \right)^{2/3} + \left( {\hat b\frac{{\Delta _t }}{{\Delta _x }}} \right)^{2/3} \leqslant 1$$ gegeben ist, wo Δ t , Δ x and δ y die Gitterabstände sind. Interessanterweise ist dieser Stabilitätsbereich identisch mit dem von Turkel für das Lax-Wendroff-Schema bestimmten Stabilitätsbereich.
    Notes: Abstract Let the two dimensional scalar advection equation be given by $$\frac{{\partial u}}{{\partial t}} = \hat a\frac{{\partial u}}{{\partial x}} + \hat b\frac{{\partial u}}{{\partial y}}.$$ We prove that the stability region of the MacCormack scheme for this equation isexactly given by $$\left( {\hat a\frac{{\Delta _t }}{{\Delta _x }}} \right)^{2/3} + \left( {\hat b\frac{{\Delta _t }}{{\Delta _x }}} \right)^{2/3} \leqslant 1$$ where Δ t , Δ x and Δ y are the grid distances. It is interesting to note that the stability region is identical to the one for Lax-Wendroff scheme proved by Turkel.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 100
    Electronic Resource
    Electronic Resource
    Springer
    Computing 56 (1996), S. 385-395 
    ISSN: 1436-5057
    Keywords: 65F05 ; 15A23 ; nCUBE/2E multiprocessors ; matrix perturbation ; parallel algorithm ; performance ; ring network ; tridiagonal Toeplitz linear systems
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Zusammenfassung Wir betrachten die Lösung einer Klasse von speziellen tridiagonalen Gleichungssystemen, die schiefsymmetrische und Töplitz-Systeme einschließt, und geben einen schnellen, parallelen, Algorithmus dafür an. Bei Vorliegen von Diagonal-Dominanz benötigt unser paralleler Solver nur Kommunikation zwischen benachbarten Prozessoren auf einem Ring-Netzwerk. Eine Fehleranalyse wird angegeben. Einige experimentelle Resultate, die auf einem nCUBE/2E Gerät gewonnen wurden, zeigen das gute Verhalten unseres stabilen, parallelen Solvers.
    Notes: Abstract The solution of special linear, circulant-tridiagonal systems is considered. In this paper, a fast parallel algorithm for solving the special tridiagonal systems, which includes the skew-symmetric and tridiagonal-Toeplitz systems, is presented. Employing the diagonally dominant property, our parallel solver does need only local communications between adjacent processors on a ring network. An error analysis is also given. On the nCUBE/2E multiprocessors, some experimental results demonstrate the good performance of our stable parallel solver.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...