1,720,972 research outputs found
Acceleration of implicit schemes for large linear systems of differential–algebraic equations
No full textInternational audienceImplicit schemes for solving large-scale linear dierential-algebraic systems with constant coef-cients necessitate at each integration step the solution of a linear system, typically obtainedby a Krylov subspace method such as GMRES. To accelerate the convergence, an approach isproposed that computes good initial guesses for each linear system to be solved in the implicitscheme. This approach requires, at each integration step, a small dimensional subspace where agood initial guess is found using the Petrov-Galerkin process. It is shown that the residual asso-ciated with the computed initial guess depends on the dimension of the subspace, the order ofthe implicit scheme, and the discretization stepsize. Several numerical illustrations are reported
Accélération de schémas d'intégration temporelle pour la résolution d'équations différentielles
No full textChaque itération de schémas d'intégration temporelle implicites, associés aux équations différentielles ordinaires ou algébriques de grande taille, nécessite la résolution d'un nombre important de systèmes linéaires ou non linéaires de grande taille. Sachant que les systèmes linéaires sont résolus via une méthode itérative, se pose alors le problème du choix de la solution initiale, autrement dit d'une approximation de la solution. Les systèmes non linéaires sont résolus via la méthode de Newton. Cette méthode calcule une suite, qui nécessite la résolution d'un grand nombre de systèmes linéaires de grande taille, et converge vers la solution du système non linéaire lorsque le premier terme de cette suite est suffisamment proche de la solution du système non linéaire. Dans cette thèse, on propose plusieurs approches permettant de calculer une bonne solution initiale, pour les systèmes linéaires utilisés dans les schémas implicites, pour la méthode de Newton et pour les systèmes linéaires utilisés dans cette méthode.When solving ordinary differential equations or algebraic-differential equations by implicit schemes, one is faced with the difficulty of solving correctly the repeated non linear and linear systems of large size that arise in the implicit schemes. In such a case, Newton-like iteration methods for solving nonlinear systems and iterative methods for linear systems can be used. The Newton-like iteration methods are based upon the idea of using a basic Newton iteration in which Newton equations are solved approximately by an available iterative method. The Newton method converges when the initial guess is close enough to a solution, so a modification is needed to guarantee convergence for arbitrary initial guess. This thesis presents a new approach to compute good initial solutions to the linear systems arising in the implicit schemes, for the Newton method and for the linear systems in the Newton method.BREST-BU Droit-Sciences-Sports (290192103) / SudocSudocFranceF
Acceleration of implicit schemes for large systems of nonlinear differential-algebraic equations
No full textWhen solving large systems of nonlinear differential-algebraic equations by implicit schemes, each integration step requires the solution of a system of large nonlinear algebraic equations. The latter is solved by an inexact Newton method which, in its turn, leads to a set of large linear systems commonly solved by a Krylov subspace iterative method. The efficiency of the whole process depends on the initial guesses for the inexact Newton and the Krylov subspace methods. An inexpensive approach is proposed and justified that computes good initial guesses for these methods. It requires a subspace of small dimension and the use of line search and trust region for the inexact Newton method and Petrov-Galerkin for the Krylov subspace method. Numerical examples are included to illustrate the effectiveness of the proposed approach
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Accélération de schémas d'intégration temporelle pour les équations différentielles algébriques linéaires
Get PDFDispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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