1,720,981 research outputs found
TRESNEI, a Matlab trust-region solver for systems of nonlinear equalities and inequalities
No full textThe Matlab implementation of a trust-region Gauss-Newton method for bound-constrained nonlinear least-squares problems is presented. The solver, called TRESNEI, is adequate for zero and small-residual problems and handles the solution of nonlinear systems of equalities and inequalities. The structure and the usage of the solver are described and an extensive numerical comparison with functions from the Matlab Optimization Toolbox is carried out
A reduced Newton method for constrained linear least-squares problems
No full textWe propose an iterative method that solves constrained linear least-squares problems by formulating them as nonlinear systems of equations and applying the Newton scheme. The method reduces the size of the linear system to be solved at each iteration by considering only a subset of the unknown variables. Hence the linear system can be solved more efficiently. We prove that the method is locally quadratic convergent. Applications to image deblurring problems show that our method gives better restored images than those obtained by projecting or scaling the solution into the dynamic range
Affine Scaling Methods for Image Deblurring Problems
No full textBlur in images can be removed by solving a series of box‐constrained linear least‐squares problems. In this paper, we compare two recent approaches for solving these problems using affine‐scaling methods. Both approaches aim at solving a nonlinear system arising from the Karush‐Kuhn‐Tucker condition. One approach is to identify the active set and update the inactive components of the iterates by using a Newton‐like method. The other is to iteratively solve the nonlinear system entry‐wise by a Quasi‐Newton method
A Gauss–Newton method for solving bound-constrained underdetermined nonlinear systems
No full textAn iterative method for solving bound-constrained underdetermined nonlinear systems is presented. The procedure consists of a Gauss--Newton method embedded into a trust–region strategy. Global and fast local convergence results are established. A specific implementation of the method is given along with its application to nonlinear systems of equalities and inequalities
New updates of incomplete LU factorizations and applications to large nonlinear systems
No full textIn this paper, we address the problem of preconditioning sequences of large sparse indefinite systems of linear equations and present two new strategies to construct approximate updates of factorized preconditioners. Both updates are based on the availability of an incomplete factorization for one matrix of the sequence and differ in the approximation of the so-called ideal update. For a general treatment, an incomplete LU (ILU) factorization is considered, but the proposed approaches apply to incomplete factorizations of symmetric matrices as well. The first strategy is an approximate diagonal update of the ILU factorization; the second strategy relies on banded approximations of the factors in the ideal update. The efficiency and reliability of the proposed preconditioners are shown in the solution of nonlinear systems of equations by preconditioned Newton–Krylov methods. Nearly matrix-free implementations of the updating strategy are provided, and numerical experiments are carried out on application problems
Trust-region quadratic methods for nonlinear systems of mixed equalities and inequalities
No full textTwo trust-region methods for systems of mixed nonlinear equalities, general inequalities and simple bounds are proposed. The first method is based on a Gauss–Newton model, the second one is based on a regularized Gauss–Newton model and results to be a Levenberg–Marquardt method. The globalization strategy uses affine scaling matrices arising in bound-constrained optimization. Global convergence results are established and quadratic rate is achieved under an error bound assumption. The numerical efficiency of the new methods is experimentally studied
Grid generation and Algebraic solvers
No full textThis work focuses on some of the most relevant numerical issues in the solution of the drift-diffusion model for semiconductor devices. The drift-diffusion model consists of an elliptic and two parabolic partial differential equations which are nonlinearly coupled. A reliable numerical approximation of this model unavoidably leads to choose a suitable tessellation of the computational domain as well as specific solvers for linear and nonlinear systems of equations. These are the two main issues tackled in this work, after introducing a classical discretization of the drift-diffusion model based on finite elements. Numerical experiments are also provided to investigate the performances both of up-to-date and of advanced numerical procedures
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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