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  • 1995-1999  (737)
  • 1990-1994  (524)
  • 1995  (737)
  • 1990  (524)
  • Engineering General  (1,261)
  • 101
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Linear Algebra with Applications 2 (1995), S. 431-445 
    ISSN: 1070-5325
    Keywords: order cone ; order unit ; K-monotone operator ; Barrier element ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: An abstract version of the well known Barrier Lemma is presented and some of its generalizations are shown for bounded linear and some unbounded densely defined linear monotone operators in some partially ordered Banach spaces. K-monotonicity of generally unbounded operators is characterized. Some applications of constructing error bounds for approximately solving equations governed by bounded linear operators are established.
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  • 102
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    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Linear Algebra with Applications 2 (1995), S. 363-393 
    ISSN: 1070-5325
    Keywords: Peaceman - Rachford procedure ; domain decomposition ; nonconforming finite element spaces ; parallel processing ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: This paper presents a general method to associate the operator splitting for the Peaceman - Rachford procedure with a decomposition of the domain in problems arising from finite element discretization of partial differential equations. The algorithm is provably convergent without any symmetry requirement. Moreover, this method possesses the significant advantage of making the linear systems of the Peaceman - Rachford iteration block diagonal and therefore perfectly appropriate for parallel processing. Not only is sparsity not affected but a reduction of the bandwidth occurs. In fact, for appropriate choices of nonconforming finite element spaces, this method makes directly possible elementwise processing. This option remains available in general for higher-dimensional problems by applying the splitting algorithm recursively. Practical implementation requires nothing more than the standard finite element assembly procedure and some bookkeeping to relate a few different orderings of the nodes. In addition to all these attractive features, the method is rapidly convergent and remains highly competitive even when used on a serial machine.
    Additional Material: 6 Ill.
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  • 103
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    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Linear Algebra with Applications 2 (1995), S. 401-414 
    ISSN: 1070-5325
    Keywords: conjugate gradient ; distributed computing ; analytic model ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: In this paper, we demonstrate the scalability of the Reduced System Conjugate Gradient (RSCG) algorithm on distributed memory architectures. We present speed-up results obtained on the Intel iPSC/860 that compare one-, two-, and three-dimensional decompositions of the domain for both positive definite and positive semidefinite test problems. We develop a model for the RSCG algorithm to analyze computational and communication costs. The model is validated using experimental data and then used to examine and predict behavior of the RSCG algorithm as a function of architecture parameters including communication latency and transmission times and memory access costs.
    Additional Material: 2 Ill.
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  • 104
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    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Linear Algebra with Applications 2 (1995), S. 481-481 
    ISSN: 1070-5325
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Type of Medium: Electronic Resource
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  • 105
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    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Linear Algebra with Applications 2 (1995), S. 467-479 
    ISSN: 1070-5325
    Keywords: generalized conjugate gradient ; orthogonal residual ; rate of convergence ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: To solve a linear system of equations with a generally nonsymmetric matrix, a generalized conjugate gradientorthogonal residual method is presented. The method uses all previous search directions (or a truncated set of them) at each step but, contrary to standard implementations of similar methods, it requires storage of only one set with a linearly growing number of vectors (or the number in the truncated set). Furthermore, there is only one vector (the residual), which must be updated using all the vectors in this set, at each step. In this respect it is similar to the popular GMRES method but it has the additional advantage that it can stop at any stage when the norm of the residual is sufficiently small and no extra computation is needed to compute this norm. Furthermore, the new method can be truncated.The rate of convergence of the method is also discussed.
    Additional Material: 3 Tab.
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  • 106
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Linear Algebra with Applications 2 (1995) 
    ISSN: 1070-5325
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Type of Medium: Electronic Resource
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  • 107
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    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Linear Algebra with Applications 2 (1995), S. ii 
    ISSN: 1070-5325
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
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  • 108
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    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Linear Algebra with Applications 2 (1995), S. 507-531 
    ISSN: 1070-5325
    Keywords: Cholesky decomposition ; singular values ; eigenvalues ; null spaces ; noise spaces ; URV and ULV factorizations ; QR algorithm ; LR algorithm ; Jacobi methods ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: The implicit Cholesky algorithm has been developed by several authors during the last 10 years but under different names. We identify the algorithm with a special version of Rutishauser's LR algorithm. Intermediate quantities in the transformation furnish several attractive approximations to the smallest singular value.The paper extols the advantages of using shifts with the algorithm. The nonorthogonal transformations improve accuracy.
    Additional Material: 4 Ill.
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  • 109
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    New York, NY [u.a.] : Wiley-Blackwell
    Numerical Linear Algebra with Applications 2 (1995), S. 543-545 
    ISSN: 1070-5325
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Type of Medium: Electronic Resource
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  • 110
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    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 11 (1995) 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
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  • 111
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    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 11 (1995), S. iii 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
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  • 112
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    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 11 (1995), S. 1-11 
    ISSN: 1069-8299
    Keywords: vibration ; spline prism method ; thick rectangular plate ; 3D elasticity theory ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The paper presents an application of the spline prism method to analyse vibration of isotropic, thick rectangular plates with two opposite edges simply supported. Three-dimensional spline prism models are formulated by combining B-spline functions with beam eigenfunctions. Because of the orthogonality of the beam functions, three-dimensional problems are reduced to a series of two-dimensional ones. To demonstrate the accuracy and convergence of the semi-numerical method, the results are compared with those obtained by other numerical methods. Good convergence and accuracy are obtained. The effects of the ratio of thickness to width and the aspect ratio on the frequencies of thick rectangular plates with several boundary conditions are analysed, and the results are compared with those calculated by the Mindlin plate theory.
    Additional Material: 2 Ill.
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  • 113
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    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 11 (1995), S. 33-40 
    ISSN: 1069-8299
    Keywords: boundary conditions ; streamfunction-vorticity equations ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The appropriate specification of boundary conditions is the main difficulty in the finite element solution of the streamfunction-vorticity equations for two-dimensional incompressible laminar flows. In this context, we show that the appropriate specification of both the outflow and the inflow boundary conditions is required for the successful modelling of two well known test problems.
    Additional Material: 3 Ill.
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  • 114
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    Communications in Numerical Methods in Engineering 11 (1995), S. 73-90 
    ISSN: 1069-8299
    Keywords: circular plate ; viscoelasticity ; equilibrium states ; deformation map ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The geometrically non-linear response of a circular plate is investigated by means of a ‘deformation map’. The plate is subjected to static radial forces and bending moments, both uniformly distributed along the supported edges, in addition to a transverse load. The deformation map gives the complete picture for the investigated structure. The classical formulation of large deformation for the above-mentioned problem goes back to Timoshenko (1940). To create a deformation map, it is necessary to convert the boundary value problem into an initial value problem (Cauchy's problem). The Runge-Kutta (RK) method can then be used to solve numerically the equilibrium equations for the above-mentioned circular plate. In the paper several kinds of transverse loading are considered and their influence on the plate response is examined. It is shown that in some cases the plate's behaviour is chaotic-like (unpredictable), in the sense that various equilibrium states are possible for a certain given set of loads. Yet, it is shown that the viscoelasticity reduces the range of the possible equilibrium states, and thus stabilizes the system.
    Additional Material: 6 Ill.
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  • 115
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    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 11 (1995) 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
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  • 116
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    Chichester : Wiley-Blackwell
    Communications in Numerical Methods in Engineering 11 (1995), S. iii 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
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  • 117
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    Communications in Numerical Methods in Engineering 11 (1995), S. 105-115 
    ISSN: 1069-8299
    Keywords: finite element method ; conceptual diagrams ; error estimation ; postprocessing ; teaching ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The success of the finite element method depends on the highly systematic way the analysis is built up, which means that the structure of the theoretical description and the code is transferable between different applications. It is advisable to teach the subject in such a way that this fact is fully exploited. It is a fact that most FE calculations today do not contain a check of the accuracy/quality of the solution. In the teaching of the FE method nothing is more important than the basic knowledge and understanding of the properties and behaviour of the obtained FE solution. The paper deals with the methodology in presenting the method, by use of conceptual diagrams. It also discusses the interpretation of the results from a classical FE analysis and the extraction of high quality information. Finally, error estimation and postprocessing are discussed. The detailed description of the boundary conditions is lost in the FE solution. In the postprocessing stage they should be taken into account once more.
    Additional Material: 9 Ill.
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  • 118
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    Communications in Numerical Methods in Engineering 11 (1995), S. 97-103 
    ISSN: 1069-8299
    Keywords: dispersion relation ; isotropy ; numerical dispersion ; stiffness integration ; zero wave speed ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The dispersion properties of plane waves, propagating in an infinite uniform mesh with linear cubic 3D finite elements, are investigated. Time discretization is performed with the central-difference time-stepping scheme in combination with lumped mass matrices. The stiffness matrices are integrated analytically with different integration schemes, and dispersion relations are derived. The results show that the stiffness integration scheme can be chosen to reduce dispersion and improve the isotropy of wave propagation. It is also observed that the numerical wave speed becomes zero along certain wave propagation directions for specific wave numbers.
    Additional Material: 3 Ill.
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  • 119
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    Communications in Numerical Methods in Engineering 11 (1995), S. 127-135 
    ISSN: 1069-8299
    Keywords: conformal mapping ; numerical grids ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: We develop some special conformal maps and related strategies for grid generation in certain ‘difficult’ domains. Of particular interest are non-convex domains, and domains with corners and cusps.
    Additional Material: 12 Ill.
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  • 120
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    Communications in Numerical Methods in Engineering 11 (1995), S. 339-345 
    ISSN: 1069-8299
    Keywords: numerical integration ; plasticity ; pressure-dependent plasticity ; porous metals ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A general methodology for the numerical integration of pressure-dependent plasticity models is developed, and the corresponding ‘linearization moduli’ are derived.
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  • 121
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    Communications in Numerical Methods in Engineering 11 (1995), S. 347-353 
    ISSN: 1069-8299
    Keywords: assumed strain methods ; Hu-Washizu principle ; stress recovery ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: An alternative justification of the B-bar procedure using the Hu-Washizu variational principle is presented. In contrast to previous work, the derivation starts from the three groups of algebraic equations (strain-displacement equations, stress-strain equations and equations of equilibrium) obtained by discretization of the Hu-Washizu functional. Based on an appropriate assumption, these equations can be manipulated to yield the element stiffness matrix in the form typical of the B-bar procedure. This approach directly leads to a stress-recovery formula different from the one suggested before. The theory is illustrated by application to a family of quadrilateral plane elements.
    Additional Material: 1 Tab.
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  • 122
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    Communications in Numerical Methods in Engineering 11 (1995), S. 630-630 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
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  • 123
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    Communications in Numerical Methods in Engineering 11 (1995), S. 765-774 
    ISSN: 1069-8299
    Keywords: spectral methods ; Chebȳshev collocation ; Galerkin collocation ; boundary layer equations ; preconditioned minimum residual ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A comparison is made between the performance of the (aliased) Chebȳshev collocation method (CM) and the more recent Galerkin collocation method (GCM), which is a least-squares collocation method, in solving the laminar, incompressible, steady boundary-layer equations, which are parabolic in nature. An iterative procedure based on the preconditioned residual minimization method has been used. It is shown that the GCM is superior to the CM on several counts. Unlike the CM, the GCM minimizes the residual uniformly over the entire domain. The global accuracy of the solution is found to be higher in the GCM, at lower grid resolutions. The method also achieves much higher convergence rates. Unlike in the collocation method, the final residual values obtained in the GCM are good indicators of the level of accuracy achieved in the solution. It is highly likely that these results will be repeatable in other systems of parabolic partial differential equations.
    Additional Material: 1 Ill.
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  • 124
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    Communications in Numerical Methods in Engineering 11 (1995), S. 789-790 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
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  • 125
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    Communications in Numerical Methods in Engineering 11 (1995) 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
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  • 126
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    Communications in Numerical Methods in Engineering 11 (1995), S. 791-792 
    ISSN: 1069-8299
    Keywords: checkerboard patterns ; P2 - P1 discontinuous pressure elements ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In this note we obtain the checkerboard patterns of P2 - P1 discontinuous pressure elements for the Stokes problem The results are more complete than those previously presented.
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  • 127
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    Communications in Numerical Methods in Engineering 11 (1995), S. 775-787 
    ISSN: 1069-8299
    Keywords: finite element theory ; explicit stiffness matrices ; hybrid stress method ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A general methodology for deriving explicit element stiffness matrices in hybrid stress formulations has recently been developed by the author. The technique utilizes special stress field transformations to eliminate the complementary energy matrix inherent to hybrid formulations, thus simplifying the stiffness definition such that an explicit evaluation can be accomplished. The elimination of numerical integration and matrix inversion results in a substantial decrease in computational cost. The methodology is applied to derive explicit algebraic expressions for the Pian-Tong hexahedral element stiffness matrix.
    Additional Material: 1 Ill.
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  • 128
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    Communications in Numerical Methods in Engineering 11 (1995), S. 995-1003 
    ISSN: 1069-8299
    Keywords: bandwidth ; ordering ; finite elements ; graphs ; algorithms ; sparsity ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Graph theoretical algorithms are presented for finite element nodal ordering to reduce the bandwidth of their stiffness matrices. Five different graphs are defined for representing the connectivity of FE models, and the problem of finite element nodal ordering is transformed into that of a graph nodal ordering. The efficiencies of these methods are compared through examples of two- and three-dimensional finite element models.
    Additional Material: 9 Ill.
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  • 129
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    Communications in Numerical Methods in Engineering 11 (1995), S. 1005-1013 
    ISSN: 1069-8299
    Keywords: infinite boundary element ; mapping ; element integration formulae ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: For elastodynamic problems in an elastic half-space, the idea of describing the displacement variation on the free ground surface outside the region being studied with the fundamental solution in a full space is presented in the paper. Then a corresponding mapped infinite boundary element is constructed for the problems of anti-plane motion. The computed results show that such an element can be applied effectively to obtain high-precision solutions.
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  • 130
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    Communications in Numerical Methods in Engineering 11 (1995), S. 1015-1024 
    ISSN: 1069-8299
    Keywords: localization ; volumetric locking ; pressure formulation ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Computation of failure mechanisms is of paramount importance for engineers assessing safety of structures. However, computation of failure loads and mechanisms presents numerical difficulties leading to wrong answers, especially in the case where failure consists in localization of plastic deformation or damage in localized zones. Here, the results depend on factors like mesh alignment and element distortion. The paper addresses the problem of designing a suitable patch test to assess element performance under localized failure. It will be shown how predictions of this test provide a reliable answer to the question of whether a particular element will or will not be suitable for such failure computations.
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  • 131
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    Communications in Numerical Methods in Engineering 11 (1995), S. 1025-1032 
    ISSN: 1069-8299
    Keywords: flux lines ; current distributions ; magnetic inverse problem ; voltage distribution ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The display of isopotential contours is a standard technique in the interpretation of results generated by the finite element analysis of voltage distribution problems. The complementary display of the current flow or flux lines is in many ways more useful intuitively, but has not been used widely in finite element analyses. We describe a simple method for generating flux line distributions, and discuss the method as applied to the reconstruction of current distributions from magnetic field maps.
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  • 132
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    Communications in Numerical Methods in Engineering 11 (1995), S. 1033-1038 
    ISSN: 1069-8299
    Keywords: electric field ; vector potential ; electrostatic ; electric force surface ; curve integral ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A finite difference algorithm for plotting the electric force surface is presented in three-dimensional electrostatic field computation. Based on the flux concept, the nodal electric flux is calculated numerically through the curve integral of the electric displacement vector which was obtained by a numerical differentiation of the nodal electric potential. This latter is calculated by a finite difference method. The electric force surface may also be plotted.
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  • 133
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    Communications in Numerical Methods in Engineering 11 (1995), S. 1047-1048 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
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  • 134
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    Numerical Linear Algebra with Applications 2 (1995), S. 415-429 
    ISSN: 1070-5325
    Keywords: indefinite ; inverse ; preconditioning ; symmetric ; Toeplitz ; Trench algorithm ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: A modification is presented of the classical O(n2) algorithm of Trench for the direct solution of Toeplitz systems of equations. The Trench algorithm is stable for symmetric matrices that are positive definite, but can be unstable for the indefinite case (and for general matrices). Our modification permits extension of the algorithm to compute approximate inverses of indefinite symmetric Toeplitz matrices, for which the unmodified algorithm breaks down when principal submatrices are singular. As a preconditioner, the approximate inverse has an advantage that only matrix - vector multiplications are required for the solution of a linear system, without forward and backward solves. The approximate inverse so obtained can be sufficiently accurate, moreover, that, when it is used as a preconditioner for the applications investigated, subsequent iteration may not even be necessary. Numerical results are given for several test matrices. The perturbation to the original matrix that defines the modification is related to a perturbation in a quantity generated in the Trench algorithm; the associated stability of the Trench algorithm is discussed.
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  • 135
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    Numerical Linear Algebra with Applications 2 (1995), S. 483-485 
    ISSN: 1070-5325
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
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  • 136
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    Numerical Linear Algebra with Applications 2 (1995), S. 447-465 
    ISSN: 1070-5325
    Keywords: preconditioned iterative methods ; SSOR factorization ; parallelization ; connection machine ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: A class of parallelizable preconditioned iterative methods for the solution of certain finite difference or finite element linear systems of equations is presented. The methods are based on calculation of approximate inverses of the SSOR factorization. The speed of the methods may be increased by making the approximation of the inverse more accurate. The construction of the preconditioning as well as the solution of the preconditioning systems (realized by matrix-vector multiplication) can be made in parallel over the total amount of meshpoints. The methods are suitable for implementation on massively parallel computers such as connection machines. Problems with constant as well as strongly varying orthotropy are examined and the methods are compared to other parallel techniques with respect to rate of convergence, computational complexity and consumed CM200 computing time. We report a small but significant decrease in computing time compared to the (until now) most frequently used completely parallel preconditioning, the Jacobi method.
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  • 137
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    Numerical Linear Algebra with Applications 2 (1995), S. 533-541 
    ISSN: 1070-5325
    Keywords: plane rotation ; shear product ; Saxpy operation ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: An algorithm for pre- or post-multiplication of a matrix by a plane rotation, using only three vector saxpy operations instead of the four vector operations usually considered necessary, is described. No auxiliary storage for overwriting is required. The method is shown to be numerically stable.
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  • 138
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    Numerical Linear Algebra with Applications 2 (1995) 
    ISSN: 1070-5325
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
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  • 139
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    Numerical Linear Algebra with Applications 2 (1995), S. 195-203 
    ISSN: 1070-5325
    Keywords: Jacobi matrix ; arrow matrix ; inverse problem ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: We consider the problem of reconstructing Jacobi matrices and real symmetric arrow matrices from two eigenpairs. Algorithms for solving these inverse problems are presented. We show that there are reasonable conditions under which this reconstruction is always possible. Moreover, it is seen that in certain cases reconstruction can proceed with little or no cancellation. The algorithm is particularly elegant for the tridiagonal matrix associated with a bidiagonal singular value decomposition.
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  • 140
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    Numerical Linear Algebra with Applications 2 (1995), S. 235-241 
    ISSN: 1070-5325
    Keywords: interior-point methods ; trust regions ; conic functions ; conjugate gradients ; linear programming ; nonlinear minimization ; Karmarkar's algorithm ; centering ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: An optimization method is developed based on ellipsoidal trust regions that are defined by conic functions. It provides a powerful unifying theory from which can be derived a variety of interesting and potentially useful optimization algorithms, in particular, conjugate-gradient-like algorithms for nonlinear minimization and Karmarkar-like interior-point algorithms for linear programming.
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  • 141
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    Numerical Linear Algebra with Applications 2 (1995), S. 219-234 
    ISSN: 1070-5325
    Keywords: nonsymmetric matrices ; sparse matrices ; eigenvalue problem ; EISPACK ; LAPACK ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: With the growing demands from disciplinary and interdisciplinary fields of science and engineering for the numerical solution of the nonsymmetric eigenvalue problem, competitive new techniques have been developed for solving the problem. In this paper we examine the state of the art of the algorithmic techniques and the software scene for the problem. Some current developments are also outlined.
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  • 142
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    Numerical Linear Algebra with Applications 2 (1995), S. 243-250 
    ISSN: 1070-5325
    Keywords: Cholesky ; norm inequality ; perturbation ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: We show that a certain matrix norm ratio studied by Parlett has a supermum that is O(\documentclass{article}\pagestyle{empty}\begin{document}$\mathop \[\sqrt n \] $\end{document}) when the chosen norm is the Frobenius norm, while it is O(log n) for the 2-norm. This ratio arises in Parlett's analysis of the Cholesky decomposition of an n by n matrix.
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  • 143
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    Numerical Linear Algebra with Applications 2 (1995), S. 271-286 
    ISSN: 1070-5325
    Keywords: linear least squares ; backward perturbations ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: Let A be an m × n matrix, b be an m-vector, and x̃ be a purported solution to the problem of minimizing ‖b  -  Ax‖2. We consider the following open problem: find the smallest perturbation E of A such that the vector x̃ exactly minimizes ‖b  -  (A+E)x‖2. This problem is completely solved when E is measured in the Frobenius norm. When using the spectral norm of E, upper and lower bounds are given, and the optimum is found under certain conditions.
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  • 144
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    Numerical Linear Algebra with Applications 2 (1995), S. 287-296 
    ISSN: 1070-5325
    Keywords: block Hessenberg matrix ; block Toeplitz matrix ; linear system ; queue ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: This paper describes a divide-and-conquer strategy for solving block Hessenberg systems. For dense matrices the method is as efficient as Gaussian elimination; however, because it works almost entirely with the original blocks, it is much more efficient for sparse matrices or matrices whose blocks can be generated on the fly. For Toeplitz matrices, the algorithm can be combined with the fast Fourier transform.
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  • 145
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    Communications in Numerical Methods in Engineering 11 (1995), S. 427-434 
    ISSN: 1069-8299
    Keywords: finite element solver ; local system ; ill-conditioning ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: While implementing Zienkiewicz and Zhu's superconvergent patch recovery method in our finite element solver, we came across two difficulties: rank deficiency of the local system to be solved, and ill-conditioning. The first problem was solved by increasing the number of sampling points and the second by using LU decomposition with partial pivoting.
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  • 146
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    Communications in Numerical Methods in Engineering 11 (1995), S. 443-453 
    ISSN: 1069-8299
    Keywords: initial post-buckling ; second-order fields ; iteration ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Second-order post-buckling fields emanate from the solutions of a constrained minimization problem. Two iterative solution algorithms for this specific type of constrained problem are described. A classical augmented Lagrangian algorithm is compared with a simpler one utilizing the specific feature of the initial post-buckling analysis. Numerical examples of prismatic plate-type structures are presented.
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  • 147
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    Communications in Numerical Methods in Engineering 11 (1995), S. 455-464 
    ISSN: 1069-8299
    Keywords: Laplacian smoothing ; grid smoothing ; surface grids ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In this note we point out the natural choice of smoothing by use of a metric tensor to maintain control of the local element stretch. The extension to grids on surfaces in 3D is straightforward. Numerical examples are given.
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  • 148
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    Communications in Numerical Methods in Engineering 11 (1995), S. 409-416 
    ISSN: 1069-8299
    Keywords: contact ; friction ; finite element method ; large deformation ; augmented Lagrangian method ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The paper is devoted to the analysis of two- or three-dimensional contact problems with Coulomb friction and large deformation. The classical approach is based on two minimum principles or two variational inequalities: the first for unilateral contact and the second for friction. A coupled approach using only one principle or one inequality is presented. This new approach allows us to extend the notion of normality law to dissipative behaviours with a non-associated flow rule, such as surface friction. Non-differentiable contact potentials are regularized by means of the augmented Lagrangian method. Using the C++ language, an object-oriented finite element database is created, which allows us to implement the contact and friction in an existing code in a very simple and neat way. Numerical examples are carried out in many difficult cases such as shock absorber and three-dimensional contact. The numerical results prove that this approach is robust and efficient concerning numerical stability.
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  • 149
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    Communications in Numerical Methods in Engineering 11 (1995), S. 435-441 
    ISSN: 1069-8299
    Keywords: regular boundary layers ; ∊-uniform numerical method ; advection-dominated transport ; piecewise uniform mesh ; singular perturbations ; numerical experiments ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Upwind finite difference operators on uniform meshes are well known to be unsuitable for the numerical solution of singularly perturbed partial differential equations, in the sense that, in the neighbourhood of the boundary layers, the error in the numerical approximation may increase as the mesh is refined. Recently, on the other hand, it has been predicted theoretically that the use of upwind finite difference operators on specially designed piecewise uniform meshes guarantees the decrease of the nodal error to zero as the number of mesh elements increases. In the paper the general theorem is quoted and its prediction is validated by numerical experiment for a specific linear advection-dominated transport equation in two dimensions. Experimental values of the convergence rate are obtained, which also agree with the theoretical estimates.
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    Communications in Numerical Methods in Engineering 11 (1995), S. 475-476 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
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  • 151
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    Keywords: Engineering ; Engineering General
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  • 152
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    Communications in Numerical Methods in Engineering 11 (1995), S. 477-478 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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  • 153
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    Communications in Numerical Methods in Engineering 11 (1995), S. 465-473 
    ISSN: 1069-8299
    Keywords: finite element analysis ; mesh optimization ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A new approach is presented to optimize the search, deletion and insertion operations in the advancing-front triangular grid generation technique. This approach is based on the heap, hash table and linked list data structures. The basic idea is to use different data structures for different operations. When the front is updated after forming an element, a hash table with doubly linked lists is used to speed up searching, deleting, and inserting operations. On the other hand, a heap is used to select the shortest side for constructing each new element. Therefore, there is a need for two copies of the generation front: one is stored in the hash table with doubly linked lists, and the other one in the heap. For each element generated, this approach is able to search for a side to be removed from the front in a constant time on average, and delete and insert a side from and into the front in O(logN) time on average, where N is the number of sides in the front. The technique is also capable of searching and selecting the shortest side from the front for creating a new element in O(1) time. Several examples are included to demonstrate the performance of the approach.
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  • 154
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    Communications in Numerical Methods in Engineering 11 (1995), S. 497-506 
    ISSN: 1069-8299
    Keywords: error estimation ; super convergent patch recovery scheme ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A comparative study of error estimators using a patch recovery scheme with those using simple nodal averaging is made for the four-noded Lagrangian quadrilateral element through two plane stress elasticity problems. It is demonstrated that error estimators using a patch recovery scheme are generally more effective and have an estimated stress field that is closer to the exact one than those using simple nodal averaging.
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  • 155
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    Communications in Numerical Methods in Engineering 11 (1995), S. 479-490 
    ISSN: 1069-8299
    Keywords: Modal reaction method ; modal participation factor ; support motion ; discrete system ; modal equivalent mass ; quasi-static decomposition ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: An efficient method, called the modal reaction method, for calculating the modal participation factors for support motion problems is proposed. It is found that modal reactions at supports proportionally describe the magnitudes of the modal participation factors. Thus, the modal participation factor for support motion problems can be calculated very efficiently, saving more than 99 per cent, for the given example with 640 degreees of freedom, of the CPU time compared with using the popular quasistatic decomposition method.
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  • 156
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    Communications in Numerical Methods in Engineering 11 (1995), S. 491-495 
    ISSN: 1069-8299
    Keywords: plate bending ; similar triangles ; scaling matrix ; stiffness and mass matrices ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: It has been noticed that the stiffness and mass matrices of a triangular plate bending element can be generated from the known stiffness and mass matrices of a similar triangular element making use of scaling matrices. This could be used to advantage in solving problems involving large degrees of freedom if the structure could be discretized into similar triangles. The idea is extended to study the free vibration of a square plate clamped on all edges with a square central cutout.
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  • 157
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    Communications in Numerical Methods in Engineering 11 (1995), S. 507-513 
    ISSN: 1069-8299
    Keywords: Dynamic stiffness ; Timoshenko beams ; vibrations ; shear deformations ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The Timoshenko beam model incorporates the effect of shear deformations and rotary inertia in the vibration response of beams. For constant cross-section beams it was shown that the effect is dependent on the aspect ratio of the beams, and for beams with large ratio the effect is small. In this work exact vibration frequencies for variable cross-section beams are found using the dynamic stiffness matrix approach. An example is given and compared with known results of beams with various taper ratios.
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  • 158
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    Communications in Numerical Methods in Engineering 11 (1995), S. 805-812 
    ISSN: 1069-8299
    Keywords: solidification ; dendritic growth ; probabilistic modelling ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A model of solidification is developed from a statistical mechanics basis that incorporates nucleation of columnar and equiaxed grains, thermal and solute diffusion, and latent heat of the phase change. The model is applied to the solidification of austenitic steel. The dendritic growth of columnar and equiaxed grains is simulated, including the segregation of solute ahead of the solid-liquid interface. The irregular branched morphology of the solid forms in a manner analogous to dendritic morphologies that arise from constitutional undercooling in real materials. There is competition between columnar and equiaxed growth. When growing grains approach, the solute layer and the thermal field act to prevent them overlapping.
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  • 159
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    Communications in Numerical Methods in Engineering 11 (1995), S. 793-803 
    ISSN: 1069-8299
    Keywords: arc-length control ; line search ; path-following ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: When solving non-linear algebraic equations resulting from a typical finite element discretization it is quite common that the popular Newton-Raphson iteration fails to converge or requires an excessive number of iterations. To solve this problem, line searches have been proposed in conjunction with load control and quadratic arc-length control, which has proved to be highly successful. In the paper we first review a number of the most popular arc-length controls. Then we highlight the severe drawbacks associated with the coupling of the cylindrical arc-length control and line searches. Next, various other forms of arc-length controls are scrutinized in the light of this coupling. It is shown that for some of the arc-length controls such a combination is extremely simple and straightforward, yet at the same time efficient and effective. For the rest the same complications incurred for the cylindrical arc-length method remain.
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  • 160
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    Communications in Numerical Methods in Engineering 11 (1995), S. 813-820 
    ISSN: 1069-8299
    Keywords: non-circular ducts ; mapping functions ; non-Newtonian fluids ; Levenberg-Marquardt algorithm ; velocity contour values ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The problem of determination of fully developed duct flows of arbitrary shape is considered for fluids obeying various constitutive equations. A numerical method based on the transformation of the physical flow (simply connected) domain into a mapped circular domain is set up. The numerical determination of the unknown transformation between the two domains leads to knowledge of the velocities and stresses in the duct, starting from circular contour values of the velocity in the mapped computational domain. Different constitutive equations are investigated for several flow geometries. The comparisons with existing analytical solutions are found to be consistent for all the geometries tested. The method may provide a useful tool for determination, in steady flow conditions, of the flow characteristics for various types of ducts and constitutive equations.
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  • 161
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    Communications in Numerical Methods in Engineering 11 (1995), S. 821-829 
    ISSN: 1069-8299
    Keywords: rotational transformations ; anisotropic elasticity ; laminates ; constitutive matrices ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In elasticity theory involving anisotropic materials, the rotational transformation of stress, strain and constitutive relations is of major importance. Also, when these problems are represented in matrix form there are several different contracted notations used to express the stress and strain tensors as column matrices. In general, the contracted notations used lead to unnecessary complications and may lead to errors. In the paper, contracted forms which yield orthonormal rotational transformations are advocated. These transformations are illustrated for stress, strain, modulus and compliance and are also applicable for strength transformation. The gains to be made are procedural and mathematically simple, leading to easier understanding.
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  • 162
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    Communications in Numerical Methods in Engineering 11 (1995), S. 831-838 
    ISSN: 1069-8299
    Keywords: coupled system ; fluid-structural interactions ; left and right eigenvector ; natural frequency ; symmetrization ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: System equations of motion for a fluid-structural coupled system are formulated and their symmetrization is presented. By using the state-variable augmentation and degree of freedom reduction technique applicable to a damped mechanical system, a new approach is proposed to transform the asymmetrical equations of motion for a coupled system into some symmetrical ones. The significance of the transformation used is discussed. The relationship is established between the left and the right eigenvectors, based on which the modal superposition method can be used in predicting dynamic responses for a general asymmetrical fluid-structural coupled system.
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  • 163
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    Communications in Numerical Methods in Engineering 11 (1995), S. 839-847 
    ISSN: 1069-8299
    Keywords: validation of FE modelling ; optical techniques ; fringe contours ; shape functions ; stress analysis ; displacement analysis ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A novel and simple approach to plot fringe contours from finite element results that simulates the fringe thickness variation as observed in experiments is presented. The procedure does not require solution of any non-linear equation. Shape functions are used as interpolation functions to plot fringe contours from the nodal values of fringe orders. The various fringe contours one usually comes across in stress analysis are also reviewed. The program code in Turbo-Pascal employing the new algorithm is given. Stress and displacement contours at the tip of a crack in an SEN (single-edge-notched) specimen are plotted using the code developed. The fringe contours plotted correspond to those observed in experiments such as photoelasticity, holography and Moire.
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  • 164
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    Communications in Numerical Methods in Engineering 11 (1995), S. 869-870 
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    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
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  • 165
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    Communications in Numerical Methods in Engineering 11 (1995), S. 849-856 
    ISSN: 1069-8299
    Keywords: conjugate gradient methods ; incompressible Navier-Stokes equations ; segregated finite volume procedure ; staggered grid ; vectorization ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: PISO (pressure-implicit with splitting of operators) is an algorithm devised to solve the transient incompressible Navier-Stokes and energy equations. In that it uses separate equations for each of two pressure corrections, velocity components and transported scalars, PISO is known as a segregated solution procedure. Preconditioned, generalized conjugate gradient (GCG) methods in combination with schemes for vectorization and storage minimization are described in the paper for the purpose of solving both the symmetric and non-symmetric algebraic equation systems that result from the PISO algorithm. Of particular interest in the paper is a comparison of the present procedure with a procedure described by Chin et al. (1992) in which preconditioned conjugate gradient methods are used to solve the Jacobian matrix used in the Newton iteration of the fully coupled non-linear equations. The two methods are similar in that both techniques are based on a discretization using staggered control volumes with the power-law method for modelling advection-diffusion transport.
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    Communications in Numerical Methods in Engineering 11 (1995), S. 857-868 
    ISSN: 1069-8299
    Keywords: adaptive analysis ; error estimate ; mesh refinement ; finite elements ; plate bending ; computations ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A new mesh refinement formulation for h-adaptive solutions of linear elliptic problems is presented. The reliability of the methods employed for estimating errors and the convergence rate of the errors during an adaptive process are investigated by means of an asymptotic analysis method. The present adaptive mesh refinement strategy significantly improves adaptivity performance and has higher error convergence rates than those usually used. Numerical examples are shown to illustrate the efficiency of the method shown.
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    Communications in Numerical Methods in Engineering 11 (1995), S. 871-871 
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    Keywords: Engineering ; Engineering General
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  • 168
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    Keywords: Engineering ; Engineering General
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  • 169
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    Communications in Numerical Methods in Engineering 11 (1995), S. 887-897 
    ISSN: 1069-8299
    Keywords: geometrically non-linear problem ; finite elasticity ; p-version ; hp-extension ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A p-version of the finite element method and an hp-extension is applied to a geometrically non-linear model problem. Starting from a standard formulation in finite elasticity, some implementation details are outlined. The robustness and efficiency of this method, as already well known for linear problems, is demonstrated. In two numerical examples high accuracy and exponential rate of convergence in energy are shown. The method presented can be used effectively in problems where standard low-order plane strain elements fail to give accurate results.
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  • 170
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    Communications in Numerical Methods in Engineering 11 (1995), S. 911-915 
    ISSN: 1069-8299
    Keywords: adaptive finite element method ; optimal mesh ; error estimate ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In the paper the authors investigate the conditions of optimal mesh, and prove that the element errors in the optimal mesh should be identical for all existing elements. Also, it is shown that the correct mesh refinement formulations should be derived at an element level rather than the global level. Thus the element permissible errors need to be determined. The method to determine these permissible element errors is described.
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    Communications in Numerical Methods in Engineering 11 (1995), S. 873-886 
    ISSN: 1069-8299
    Keywords: k-∊-γ model ; turbulent intermittency ; wake ; aerofoil ; non-staggered FUM ; branch-cut ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The whole turbulent flow field around a two-dimensional aerofoil is solved with a consistent numerical method on a single-grid system and with an intermittency implemented two-equation model, namely the k-∊-γ turbulence model in elliptic form. In order to solve the numerical instability problem arising from the branch-cut in C-type grids using the non-staggered finite-volume method, a new numerical technique is proposed to guarantee the correct velocity-pressure coupling along the branch-cut. The computational results are compared with those by the standard k-∊ model and experimental data. This study demonstrates the relative simplicity of the present C-type single grid system, and the capability is assessed of the k-∊-γ equations for predicting turbulent flows consisting of both wall-free and wall-bounded regions.
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    Communications in Numerical Methods in Engineering 11 (1995), S. 899-909 
    ISSN: 1069-8299
    Keywords: finite element method ; non-linear shell elements ; assumed strain approach ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: A quadrilateral degenerated C0 shell element is presented which relies on extensible director kinematics and which incorporates unmodified three-dimensional constitutive models. It is shown that the direct interpolation of the extensible director field causes severe locking behaviour in the case of thin shell structures. An assumed strain interpolation is proposed to overcome the thin-shell defect. Due to this modification the shell element is able to accommodate large rotations without a rotation tensor, even for very thin shells. Several large deformation examples confirm that the developed shell element is competitive with more elaborate formulations which use rotational degrees of freedom.
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  • 173
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    Communications in Numerical Methods in Engineering 11 (1995), S. 927-935 
    ISSN: 1069-8299
    Keywords: incompressible continuum ; fundamental solutions ; boundary element method ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Novel fundamental solutions for elastodynamics of fully incompressible media are derived, by reason of their many applications to engineering and physical problems. It is demonstrated that, when Poisson's ratio equals 1/2, the frequency domain fundamental solutions (Stokes's solutions) are independent of the dilatational wave velocity, which tends to infinity. Consequently, dynamic problems involving incompressible materials can be rigorously analysed by the boundary element method without special difficulty. Numerical solutions to geotechnical problems of incompressible half-spaces are presented to demonstrate the applicability and accuracy of the formulations.
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  • 174
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    Communications in Numerical Methods in Engineering 11 (1995), S. 917-925 
    ISSN: 1069-8299
    Keywords: stream-tube method ; Levenberg-Marquardt method ; viscoelastic fluids ; trust region (TR) algorithm ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: Numerical simulation of complex flows of viscoelastic fluids requires us to use efficient algorithms for solving the non-linear governing equations. The stream-tube analysis permits calculation of such flows by considering elementary subdomains in a mapped computational domain where the transformed streamlines are parallel and straight. The consideration of subregions leads us to use optimization procedures. The paper concerns the application of such algorithms to compute main flows in axisymmetric converging geometries, for fluids obeying memory-integral constitutive equations.
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  • 175
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    Communications in Numerical Methods in Engineering 11 (1995), S. 937-950 
    ISSN: 1069-8299
    Keywords: thermal convection ; slender multigrid ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The flow in a shallow, laterally heated air-filled cavity is investigated numerically using a primitive variable formulation of the governing equations of motion. Solutions are obtained for the entire flow field using a coupled solver combined with an FAS non-linear multigrid convergence accelerator. While care is taken to use a high-order, bounded discretization scheme for convective transport, the overall stability and efficiency of the approach is enhanced through the use of defect correction. This combination of features enables solutions to be found on extremely fine grids. Results for the flow in the end region of such cavities are compared qualitatively with the predictions of asymptotic theory for large aspect ratio, A (length:height), up to values of A higher than previously reported (A= 100); the particular case of A = 20 is considered for Rayleigh numbers in the range 103 to 108. Finally it is demonstrated how such solutions can be further enhanced by using locally refined grids in the end regions.
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  • 176
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    Communications in Numerical Methods in Engineering 11 (1995), S. 951-961 
    ISSN: 1069-8299
    Keywords: enhanced strain method ; finite elastoplasticity ; hourglassing ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The stability of a class of geometrically non-linear assumed enhanced strain elements is addressed. By means of an eigenvalue analysis of element tangent stiffnesses at finitely deformed configurations, circumstances under which enhanced elements become unstable, with possible development of non-physical hourglass patterns, are identified. Insight into the influence of spurious eigenvalues on the stability of solution of finite elasticity and elastoplasticity problems is provided by simple numerical tests with a patch of elements. Results of simulations of some practical engineering problems are presented and limitations on the applicability of enhanced strain elements in the finite strain regime are discussed.
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  • 177
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    Communications in Numerical Methods in Engineering 11 (1995), S. 963-964 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
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  • 178
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    Communications in Numerical Methods in Engineering 11 (1995) 
    ISSN: 1069-8299
    Keywords: Engineering ; Engineering General
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  • 179
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    Communications in Numerical Methods in Engineering 11 (1995), S. 965-970 
    ISSN: 1069-8299
    Keywords: least-square finite element ; Stokes problem ; mass conservation ; incompressible flow ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: In the paper the simulation of incompressible flow in 2D by the least-squares finite element method (LSFEM) in the velocity-vorticity-pressure version is studied. A problem with this method is that it does not conserve mass exactly, i.e. div uh ≠ 0 exactly. In the paper a modified LSFEM is developed which enforces a near zero residual of mass conservation, i.e. div u is nearly zero at every point of the discretization. This is accomplished by adding an extra restriction in the divergence free equation through the Lagrange multiplier strategy.
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  • 180
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    Communications in Numerical Methods in Engineering 11 (1995), S. 971-980 
    ISSN: 1069-8299
    Keywords: stochastic boundary element method ; domain integration ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: The contributions of distributed sources to the mathematical expectations and variances of the response variables are analysed in the paper using the stochastic boundary element method. The validity and the accuracy of the particular integral approach in representing statistical properties of the domain are investigated. To this end domain integration techniques to calculate the contributions of the distributed sources and their derivatives with respect to random variables that may represent both random configuration of the domain and random material parameter are developed. Several models for the random interior are presented and their influence on the response statistics is investigated. The accuracy of the particular integral approach is demonstrated through numerical comparisons with the direct integration formulation.
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  • 181
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    Numerical Linear Algebra with Applications 2 (1995), S. 17-28 
    ISSN: 1070-5325
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: The incomplete Cholesky decomposition is known as an excellent smoother in a multigrid iteration and as a preconditioner for the conjugate gradient method. However, the existence of the decomposition is only ensured if the system matrix is an M-matrix. It is well-known that finite element methods usually do not lead to M-matrices. In contrast to this restricting fact, numerical experiments show that, even in cases where the system matrix is not an M-matrix the behaviour of the incomplete Cholesky decomposition apparently does not depend on the structure of the grid. In this paper the behaviour of the method is investigated theoretically for a model problem, where the M-matrix condition is violated systematically by a suitable perturbation. It is shown that in this example the stability of the incomplete Cholesky decomposition is independent of the perturbation and that the analysis of the smoothing property can be carried through. This can be considered as a generalization of the results for the so called square-grid triangulation, as has been established by Wittum in [12] and [11].
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  • 182
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    Numerical Linear Algebra with Applications 2 (1995), S. 79-83 
    ISSN: 1070-5325
    Keywords: Engineering ; Engineering General
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    Topics: Mathematics
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  • 183
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  • 184
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    Numerical Linear Algebra with Applications 2 (1995), S. 29-49 
    ISSN: 1070-5325
    Keywords: Backward error ; Conditioning ; Matrix equations ; Riccati equations ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: In this paper, a new backward error criterion, together with a sensitivity measure, is presented for assessing solution accuracy of nonsymmetric and symmetric algebraic Riccati equations (AREs). The usual approach to assessing reliability of computed solutions is to employ standard perturbation and sensitivity results for linear systems and to extend them further to AREs. However, such methods are not altogether appropriate since they do not take account of the underlying structure of these matrix equations. The approach considered here is to first compute the backward error of a computed solution X̂ that measures the amount by which data must be perturbed so that X̂ is the exact solution of the perturbed original system. Conventional perturbation theory is used to define structured condition numbers that fully respect the special structure of these matrix equations. The new condition number, together with the backward error of computed solutions, provides accurate estimates for the sensitivity of solutions. Optimal perturbations are then used in an iterative refinement procedure to give further more accurate approximations of actual solutions. The results are derived in their most general setting for nonsymmetric and symmetric AREs. This in turn offers a unifying framework through which it is possible to establish similar results for Sylvester equations, Lyapunov equations, linear systems, and matrix inversions.
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  • 185
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    Numerical Linear Algebra with Applications 2 (1995), S. 85-85 
    ISSN: 1070-5325
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
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  • 186
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    Numerical Linear Algebra with Applications 2 (1995), S. 51-77 
    ISSN: 1070-5325
    Keywords: Arnoldi procedure ; Spread and condensed eigenvalues ; Eigenvalue translations ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: The paper considers a possible approach to the construction of high-quality preconditionings for solving large sparse unsymmetric offdiagonally dominant, possibly indefinite linear systems. We are interested in the construction of an efficient iterative method which does not require from the user a prescription of several problem-dependent parameters to ensure the convergence, which can be used in the case when only a procedure for multiplying the coefficient matrix by a vector is available and which allows for an efficient parallel/vector implementation with only one additional assumption that the most of eigenvalues of the coefficient matrix are condensed in a vicinity of the point 1 of the complex plane. The suggested preconditioning strategy is based on consecutive translations of groups of spread eigenvalues into a vicinity of the point 1. Approximations to eigenvalues to be translated are computed by the Arnoldi procedure at several GMRES(k) iterations. We formulate the optimization problem to find optimal translations, present its suboptimal solution and prove the numerical stability of consecutive translations. The results of numerical experiments with the model CFD problem show the efficiency of the suggested preconditioning strategy.
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  • 187
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    Numerical Linear Algebra with Applications 2 (1995), S. 87-93 
    ISSN: 1070-5325
    Keywords: QR algorithm ; zero pattern ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: The QR algorithm is a basic algorithm for computing the eigenvalues of dense matrices. For efficiency reasons it is prerequisite that the algorithm is applied only after the original matrix has been reduced to a matrix of a particular shape, most notably Hessenberg and tridiagonal, which is preserved during the iterative process. In certain circumstances a reduction to another matrix shape may be advantageous. In this paper, we identify which zero patterns of symmetric matrices are preserved under the QR algorithm.
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  • 188
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    Numerical Linear Algebra with Applications 2 (1995), S. 95-113 
    ISSN: 1070-5325
    Keywords: arrowhead matrix ; band matrix ; inverse eigenvalue problem ; givens rotations ; singular value decomposition ; updating ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: Various plane rotation patterns are presented, which provide stable algorithms for reducing a b-band matrix bordered by p rows and/or columns to (b + p)-band form. These schemes generalize previously presented O(N2) reduction algorithms for matrices of order N, b = 1, and p = 1 to the reduction of more general b-band, p-bordered matrices where b ≥ 1 and p ≥ 1. Moreover, by splitting the matrix into two similarly structured submatrices and chasing nonzeros to the corners in two directions, the newly proposed patterns reduce the number of required rotations and hence the computational cost by one half compared to the other existing one-way chasing algorithms. Symmetric, as well as more general matrices, are considered. An example of the first type is the symmetric arrowhead matrix that arises in solving inverse eigenvalue problems. Examples of the second type are found in updating the singular value decomposition (SVD) and the partial SVD.
    Additional Material: 7 Ill.
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  • 189
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    Numerical Linear Algebra with Applications 2 (1995), S. 115-133 
    ISSN: 1070-5325
    Keywords: Krylov subspace ; Lanczos process ; symmetric matrix ; conjugate gradients ; minimum residual ; Lehmann intervals ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: Approximations to the solution of a large sparse symmetric system of equations are considered. The conjugate gradient and minimum residual approximations are studied without reference to their computation. Several different bases for the associated Krylov subspace are used, including the usual Lanczos basis. The zeros of the iteration polynomial for the minimum residual approximation (harmonic Ritz values) are characterized in several ways and, in addition, attractive convergence properties are established. The connection of these harmonic Ritz values to Lehmann's optimal intervals for eigenvalues of the original matrix appears to be new.
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  • 190
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    Numerical Linear Algebra with Applications 2 (1995), S. 155-171 
    ISSN: 1070-5325
    Keywords: condition number ; norm of a matrix ; matrix completion ; dilation theory ; robust regularization of descriptor systems ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: We study the problem of minimizing the norm, the norm of the inverse and the condition number with respect to the spectral norm, when a submatrix of a matrix can be chosen arbitrarily. For the norm minimization problem we give a different proof than that given by Davis/Kahan/Weinberger. This new approach can then also be used to characterize the completions that minimize the norm of the inverse. For the problem of optimizing the condition number we give a partial result.
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  • 191
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    Numerical Linear Algebra with Applications 2 (1995), S. 191-194 
    ISSN: 1070-5325
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
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  • 192
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    Numerical Linear Algebra with Applications 2 (1995), S. 173-190 
    ISSN: 1070-5325
    Keywords: block algorithm ; LAPACK ; level 3 BLAS ; iterative refinement ; LU factorization ; backward error analysis ; block diagonal dominance ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: Many of the currently popular ‘block algorithms’ are scalar algorithms in which the operations have been grouped and reordered into matrix operations. One genuine block algorithm in practical use is block LU factorization, and this has recently been shown by Demmel and Higham to be unstable in general. It is shown here that block LU factorization is stable if A is block diagonally dominant by columns. Moreover, for a general matrix the level of instability in block LU factorization can be bounded in terms of the condition number K(A) and the growth factor for Gaussian elimination without pivoting. A consequence is that block LU factorization is stable for a matrix A that is symmetric positive definite or point diagonally dominant by rows or columns as long as A is well-conditioned.
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  • 193
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    Numerical Linear Algebra with Applications 2 (1995), S. 135-153 
    ISSN: 1070-5325
    Keywords: orthogonal projection ; numerical rank ; total least squares ; rank revealing QR factorization ; acute perturbation ; subspace angle ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: Overdetermined linear systems often arise in applications such as signal processing and modern communication. When the overdetermined system of linear equations AX ≍ B has no solution, compatibility may be restored by an orthogonal projection method. The idea is to determine an orthogonal projection matrix P by some method M such that [à B̃] = P[A B], and ÃX = B̃ is compatible. Denote by XM the minimum norm solution to ÃX = B̃ using method M. In this paper conditions for compatibility of the lower rank approximation and subspace properties of à in relation to the nearest rank-k matrix to A are discussed. We find upper and lower bounds for the difference between the solution XM and the SVD-based total least squares (TLS) solution XSVD and also provide a perturbation result for the ordinary TLS method. These results suggest a new algorithm for computing a total least squares solution based on a rank revealing QR factorization and subspace refinement. Numerical simulations are included to illustrate the conclusions.
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  • 194
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    Keywords: Engineering ; Engineering General
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  • 195
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    Numerical Linear Algebra with Applications 2 (1995), S. 251-269 
    ISSN: 1070-5325
    Keywords: eigenvalues ; eigenvectors ; symmetric matrices ; Rayleigh quotient iteration ; convergence ; basins of attraction ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: The Rayleigh quotient iteration method finds an eigenvector and the corresponding eigenvalue of a symmetric matrix. This is a fundamental problem in science and engineering. Parlett and Kahan have shown, in 1968, that for almost any initial vector in the unit sphere, the Rayleigh quotient iteration method converges to some eigenvector. In this paper, the regions of the unit sphere which include all possible initial vectors converging to a specific eigenvector are studied. The generalized eigenvalue problem Ax = λBx is considered. It is shown that the regions do not change when the matrix is shifted or multiplied by a scalar. These regions are completely characterized in the three-dimensional case. It is shown that, in this case, the area of the region of convergence corresponding to the interior eigenvalue is larger than the area of those corresponding to any extreme one. This can be interpreted, with the appropriate choice of probability distribution, as: the probability of converging to an eigenvector corresponding to the interior eigenvalue is larger than the probability of converging to an eigenvector corresponding to any extreme eigenvalue. It is conjectured that the same is true for matrices of any order. Experiments in higher dimensions are presented which conform with the conjecture.
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  • 196
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    Numerical Linear Algebra with Applications 2 (1995), S. 205-217 
    ISSN: 1070-5325
    Keywords: Lanczos method ; spectral Lanczos ; decompostion method ; eigenpairs ; matrix functions ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: Many researchers are now working on computing the product of a matrix function and a vector, using approximations in a Krylov subspace. We review our results on the analysis of one implementation of that approach for symmetric matrices, which we call the spectral lanczos decomposition method (SLDM).We have proved a general convergence estimate, relating SLDM error bounds to those obtained through approximation of the matrix function by a part of its Chebyshev series. Thus, we arrived at effective estimates for matrix functions arising when solving parabolic, hyperbolic and elliptic partial differential equations. We concentrate on the parabolic case, where we obtain estimates that indicate superconvergence of SLDM. For this case a combination of SLDM and splitting methods is also considered and some numerical results are presented.We implement our general estimates to obtain convergence bounds of Lanczos approximations to eigenvalues in the internal part of the spectrum. Unlike Kaniel-Saad estimates, our estimates are independent of the set of eigenvalues between the required one and the nearest spectrum bound.We consider an extension of our general estimate to the case of the simple Lanczos method (without reorthogonalization) in finite computer arithmetic which shows that for a moderate dimension of the Krylov subspace the results, proved for the exact arithmetic, are stable up to roundoff.
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    Numerical Linear Algebra with Applications 2 (1995), S. 311-312 
    ISSN: 1070-5325
    Keywords: Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
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    Numerical Linear Algebra with Applications 2 (1995), S. 313-315 
    ISSN: 1070-5325
    Keywords: Engineering ; Engineering General
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    Numerical Linear Algebra with Applications 2 (1995), S. 297-310 
    ISSN: 1070-5325
    Keywords: dynamical systems ; eigenvalues ; QR algorithm ; Francis shift ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics
    Notes: For many years techniques from numerical analysis have been applied fruitfully to the study of dynamical systems. In this paper it is shown that the theory of dynamical systems may be applied to certain computational problems. In particular the question of global convergence of various QR algorithms can be reduced to the study of certain vector iterations derived from Schur forms of matrices. The technique is illustrated in determining the convergence behavior of normal Hessenberg matrices under the Francis and multishift QR iterations.
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    Keywords: Engineering ; Engineering General
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