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| 2. |
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| 3. |
- Barakitis, Nikos, et al.
(författare)
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Preconditioners for fractional diffusion equations based on the spectral symbol
- 2022
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Ingår i: Numerical Linear Algebra with Applications. - : John Wiley & Sons. - 1070-5325 .- 1099-1506. ; 29:5
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Tidskriftsartikel (refereegranskat)abstract
- It is well known that the discretization of fractional diffusion equations with fractional derivatives , using the so-called weighted and shifted Grünwald formula, leads to linear systems whose coefficient matrices show a Toeplitz-like structure. More precisely, in the case of variable coefficients, the related matrix sequences belong to the so-called generalized locally Toeplitz class. Conversely, when the given FDE has constant coefficients, using a suitable discretization, we encounter a Toeplitz structure associated to a nonnegative function, called the spectral symbol, having a unique zero at zero of real positive order between one and two. For the fast solution of such systems by preconditioned Krylov methods, several preconditioning techniques have been proposed in both the one- and two-dimensional cases. In this article we propose a new preconditioner denoted bywhich belongs to the -algebra and it is based on the spectral symbol. Comparing with some of the previously proposed preconditioners, we show that although the low band structure preserving preconditioners are more effective in the one-dimensional case, the new preconditioner performs better in the more challenging multi-dimensional setting.
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| 4. |
- Barbarino, Giovanni, et al.
(författare)
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Matrix-Less Eigensolver for Large Structured Matrices
- 2021
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Sequences of structured matrices of increasing size arise in many scientific applications and especially in the numerical discretization of linear differential problems. We assume as a working hypothesis that the eigenvalues of a matrix X_n belonging to a sequence of this kind are given by a regular expansion. Based on this working hypothesis, which is illustrated to be plausible through numerical experiments, we propose an eigensolver for the computation of the eigenvalues of X_n for large n and we provide a theoretical analysis of its convergence. The eigensolver is called matrix-less because it does not operate on the matrix X_n but on a few similar matrices of smaller size combined with an interpolation-extrapolation strategy. Its performance is benchmarked on several numerical examples, with a special focus on matrices arising from the discretization of differential problems.
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| 5. |
- Barbarino, Giovanni, et al.
(författare)
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Matrix-Less Eigensolver for Large Structured Matrices
- 2021
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Sequences of structured matrices of increasing size arise in many scientific applications and especially in the numerical discretization of linear differential problems. We assume as a working hypothesis that the eigenvalues of a matrix X_n belonging to a sequence of this kind are given by a regular expansion. Based on the working hypothesis, which is proved to be plausible through numerical experiments, we propose an eigensolver for the computation of the eigenvalues of X_n for large n. The performance of the eigensolver—which is called matrix-less because it does not operate on the matrix X_n—is illustrated on several numerical examples, with a special focus on matrices arising from the discretization of differential problems, and turns out to be quite satisfactory in all cases. In a sense, this is an a posteriori proof of the reasonableness of the working hypothesis as well as a testimony of the fact that the spectra of large structured matrices are much more “regular” than one might expect.
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| 6. |
- Bargholtz, Chr., et al.
(författare)
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Measurement of the eta -> pi(+)pi(-)e(+)e(-) decay branching ratio
- 2007
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Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 644:5-6, s. 299-303
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Tidskriftsartikel (refereegranskat)abstract
- The reaction pd -> He-3 eta at threshold was used to provide a clean source of eta mesons for decay studies with the WASA detector at CELSIUS. The branching ratio of the decay eta -> pi(+)pi(-)e(+)e(-) is measured to be (4.3 +/- 1.3 +/- 0.4) x 10(-4).
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| 7. |
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| 8. |
- Berggren, Martin, et al.
(författare)
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A discontinuous Galerkin extension of the vertex-centered edge-based finite volume method
- 2009
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Ingår i: Communications in Computational Physics. - 1815-2406. ; 5:2-4, s. 456-468
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Tidskriftsartikel (refereegranskat)abstract
- The finite volume (FV) method is the dominating discretization technique for computational fluid dynamics (CFD), particularly in the case of compressible fluids. The discontinuous Galerkin (DG) method has emerged as a promising high-accuracy alternative. The standard DG method reduces to a cell-centered FV method at lowest order. However, many of today's CFD codes use a vertex-centered FV method in which the data structures are edge based. We develop a new DG method that reduces to the vertex-centered FV method at lowest order, and examine here the new scheme for scalar hyperbolic problems. Numerically, the method shows optimal-order accuracy for a smooth linear problem. By applying a basic hp-adaption strategy, the method successfully handles shocks. We also discuss how to extend the FV edge-based data structure to support the new scheme. In this way, it will in principle be possible to extend an existing code employing the vertex-centered and edge-based FV discretization to encompass higher accuracy through the new DG method.
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| 9. |
- Berlowski, M., et al.
(författare)
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Measurement of eta meson decays into lepton-antilepton pairs
- 2008
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Ingår i: Physical Review D. Particles and fields. - : American Physical Society. - 0556-2821 .- 1089-4918. ; 77:3, s. 032004-
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Tidskriftsartikel (refereegranskat)abstract
- A search for rare lepton decays of the eta meson was performed using the WASA detector at CELSIUS. Two candidates for double Dalitz decay eta -> e(+)e(-)e(+)e(-) events are reported with a background of 1.3 +/- 0.2 events. This allows to set an upper limit to the branching ratio of 9.7x10(-5) (90% CL). The branching ratio for the decay eta -> e(+)e(-)gamma is determined to (7.8 +/- 0.5(stat)+/- 0.8(syst))x10(-3) in agreement with world average value. An upper limit (90% CL) for the branching ratio for the eta -> e(+)e(-) decay is 2.7x10(-5) and a limit for the sum of the eta ->mu(+)mu(-)mu(+)mu(-) and eta ->pi(+)pi(-)mu(+)mu(-) decays is 3.6x10(-4).
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| 10. |
- Bogoya, Manuel, et al.
(författare)
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Fast Toeplitz eigenvalue computations, joining interpolation-extrapolation matrix-less algorithms and simple-loop theory
- 2022
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Ingår i: Numerical Algorithms. - : Springer Nature. - 1017-1398 .- 1572-9265. ; :91, s. 1653-1676
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Tidskriftsartikel (refereegranskat)abstract
- Under appropriate technical assumptions, the simple-loop theory allows to derive various types of asymptotic expansions for the eigenvalues of Toeplitz matrices generated by a function f. Independently and under the milder hypothesis that f is even and monotone over [0,π], matrix-less algorithms have been developed for the fast eigenvalue computation of large Toeplitz matrices, within a linear complexity in the matrix order: behind the high efficiency of such algorithms there are the expansions predicted by the simple-loop theory, combined with the extrapolation idea. Here we focus our attention on a change of variable, followed by the asymptotic expansion of the new variable, and we adapt the matrix-less algorithm to the considered new setting. Numerical experiments show a higher precision (till machine precision) and the same linear computation cost, when compared with the matrix-less procedures already presented in the relevant literature. Among the advantages, we concisely mention the following: (a) when the coefficients of the simple-loop function are analytically known, the algorithm computes them perfectly; (b) while the proposed algorithm is better or at worst comparable to the previous ones for computing the inner eigenvalues, it is vastly better for the computation of the extreme eigenvalues; a mild deterioration in the quality of the numerical experiments is observed when dense Toeplitz matrices are considered, having generating function of low smoothness and not satisfying the simple-loop assumptions.
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| 11. |
- Bogoya, Manuel, et al.
(författare)
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Matrix-less methods for the spectral approximation of large non-Hermitian Toeplitz matrices : A concise theoretical analysis and a numerical study
- 2024
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Ingår i: Numerical Linear Algebra with Applications. - : Wiley. - 1070-5325 .- 1099-1506.
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Tidskriftsartikel (refereegranskat)abstract
- It is known that the generating function of a sequence of Toeplitz matrices may not describe the asymptotic distribution of the eigenvalues of the considered matrix sequence in the non-Hermitian setting. In a recent work, under the assumption that the eigenvalues are real, admitting an asymptotic expansion whose first term is the distribution function, fast algorithms computing all the spectra were proposed in different settings. In the current work, we extend this idea to non-Hermitian Toeplitz matrices with complex eigenvalues, in the case where the range of the generating function does not disconnect the complex field or the limiting set of the spectra, as the matrix-size tends to infinity, has one nonclosed analytic arc. For a generating function having a power singularity, we prove the existence of an asymptotic expansion, that can be used as a theoretical base for the respective numerical algorithm. Different generating functions are explored, highlighting different numerical and theoretical aspects; for example, non-Hermitian and complex symmetric matrix sequences, the reconstruction of the generating function, a consistent eigenvalue ordering, the requirements of high-precision data types. Several numerical experiments are reported and critically discussed, and avenues of possible future research are presented.
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| 12. |
- Bolten, Matthias, et al.
(författare)
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A note on the spectral analysis of matrix sequences via GLT momentary symbols : from all-at-once solution of parabolic problems to distributed fractional order matrices
- 2023
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Ingår i: Electronic Transactions on Numerical Analysis. - : Osterreichische Akademie der Wissenschaften, Verlag. - 1068-9613. ; 58, s. 136-163
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Tidskriftsartikel (refereegranskat)abstract
- The first focus of this paper is the characterization of the spectrum and the singular values of the coefficient matrix stemming from the discretization of a parabolic diffusion problem using a space-time grid and secondly from the approximation of distributed-order fractional equations. For this purpose we use the classical GLT theory and the new concept of GLT momentary symbols. The first permits us to describe the singular value or eigenvalue asymptotic distribution of the sequence of the coefficient matrices. The latter permits us to derive a function that describes the singular value or eigenvalue distribution of the matrix of the sequence, even for small matrix sizes, but under given assumptions. The paper is concluded with a list of open problems, including the use of our machinery in the study of iteration matrices, especially those concerning multigrid-type techniques.
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| 13. |
- Bolten, Matthias, et al.
(författare)
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Toeplitz momentary symbols : definition, results, and limitations in the spectral analysis of structured matrices
- 2022
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Ingår i: Linear Algebra and its Applications. - : Elsevier BV. - 0024-3795 .- 1873-1856. ; 651, s. 51-82
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Tidskriftsartikel (refereegranskat)abstract
- A powerful tool for analyzing and approximating the singular values and eigenvalues of structured matrices is the theory of Generalized Locally Toeplitz (GLT) sequences. By the GLT theory one can derive a function, called the symbol, which describes the singular value or the eigenvalue distribution of the sequence, the latter under precise assumptions. However, for small values of the matrix-size of the considered sequence, the approximations may not be as good as it is desirable, since in the construction of the GLT symbol one disregards small norm and low-rank perturbations. On the other hand, Local Fourier Analysis (LFA) can be used to construct polynomial symbols in a similar manner for discretizations, where the geometric information is present, but the small norm perturbations are retained. The main focus of this paper is the introduction of the concept of sequence of "Toeplitz momentary symbols", associated with a given sequence of truncated Toeplitz-like matrices. We construct the symbol in the same way as in the GLT theory, but we keep the information of the small norm contributions. The low-rank contributions are still disregarded, and we give an idea on the reason why this is negligible in certain cases and why it is not in other cases, being aware that in presence of high nonnormality the same low-rank perturbation can produce a dramatic change in the eigenvalue distribution. Moreover, a difference with respect to the LFA symbols is that GLT symbols and Toeplitz momentary symbols are more general -just Lebesgue measurable -and are applicable to a larger class of matrices, while in the LFA setting only trigonometric polynomials are considered and more specifically those related to the approximation stencils. We show the applicability of the approach which leads to higher accuracy in some cases, when approximating the singular values and eigenvalues of Toeplitz-like matrices using Toeplitz momentary symbols, compared with the GLT symbol. Finally, since for many applications and their analysis it is often necessary to consider non-square Toeplitz matrices, we formalize and provide some useful definitions, applicable for non-square Toeplitz momentary symbols.
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| 14. |
- Chen, Minghua, et al.
(författare)
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A Multigrid method for nonlocal problems : non-diagonally dominant Toeplitz-plus-tridiagonal systems
- 2020
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Ingår i: SIAM Journal on Matrix Analysis and Applications. - 0895-4798 .- 1095-7162. ; 41:4, s. 1546-1570
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Tidskriftsartikel (refereegranskat)abstract
- Nonlocal problems have been used to model very different applied scientific phenomena which involve the fractional Laplacian when one looks at the Lévy processes and stochastic interfaces. This paper deals with the nonlocal problems on a bounded domain where the stiffness matrices of the resulting systems are Toeplitz plus tridiagonal or far from being diagonally dominant as occurs when dealing with linear finite element approximations. By exploiting a weakly diagonally dominant Toeplitz property of the stiffness matrices, the optimal convergence of the two-grid method is well established in [Fiorentino and Serra-Capizzano, SIAM J. Sci. Comput., 17 (1996), pp. 1068–1081; Chen and Deng, SIAM J. Matrix Anal. Appl., 38 (2017), pp. 869–890], and there are still questions about the best ways to define the coarsening and interpolation operators when the stiffness matrix is far from being weakly diagonally dominant [Stüben, J. Comput. Appl. Math., 128 (2001), pp. 281–309]. In this work, using spectral indications from our analysis of the involved matrices, the simple (traditional) restriction operator and prolongation operator are employed in order to handle general algebraic systems which are neither Toeplitz nor weakly diagonally dominant corresponding to the fractional Laplacian kernel and the constant kernel, respectively. We focus our efforts on providing the detailed proof of the convergence of the two-grid method for such situations. Moreover, the convergence of the full multigrid is also discussed with the constant kernel. The numerical experiments are performed to verify the convergence with only O(NlogN) complexity by the fast Fourier transform, where N is the number of the grid points.
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| 15. |
- Coco, Armando, et al.
(författare)
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Spectral and norm estimates for matrix-sequences arising from a finite difference approximation of elliptic operators
- 2023
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Ingår i: Linear Algebra and its Applications. - : Elsevier. - 0024-3795 .- 1873-1856. ; 667, s. 10-43
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Tidskriftsartikel (refereegranskat)abstract
- When approximating elliptic problems by using specialized approximation techniques, we obtain large structured matrices whose analysis provides information on the stability of the method. Here we provide spectral and norm estimates for matrix-sequences arising from the approximation of the Laplacian via ad hoc finite differences. The analysis involves several tools from matrix theory and in particular from the setting of Toeplitz operators and Generalized Locally Toeplitz matrix-sequences. Several numerical experiments are conducted, which confirm the correctness of the theoretical findings.
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| 16. |
- Dahl, Viktor, 1979-
(författare)
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Breaking the law : adolescents' involvement in illegal political activitiy
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Illegal political activity has always been part of a democratic society. Despite this, not much is known about young people’s involvement in these political activities. Research portrays political influence attempts of this kind in different terms; as troublesome for the democratic political system, as expressions of conscious decisions vital for humanity’s future, and yet other times as illustrations of a coming-of-age rebellion. Overall there is a lack of collective knowledge on illegal political activity, and especially in adolescence – the age period when these political activities seem to peak.The aim of this dissertation is therefore to enhance knowledge of involvement in illegal political activity in adolescence. This dissertation addresses this task in four empirical studies. Results show that mostly boys engage politically with illegal political means. Adolescents involved are also interested in politics, believe in their own abilities to take part in political activities, have long-term political goals, and approve of violent political tactics. In addition, these activities also seem to associate with a challenge of authority. This could be seen in how political dissatisfaction was translated into illegal political activity, and in the way these activities seemed to be reactions to a non legitimized parental authority. Besides authority challenges, these activities are likely the result of important peer relations; influences from peers with experiences of illegal political activity seem to be a most probable answer to why adolescents adopt these political means. Taken together, the results of this dissertation show that adolescents involved in illegal political activity are well-equipped for political involvement, challenge authorities in most contexts of their lives, and are likely to adopt these political means from already involved peers.
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| 17. |
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| 18. |
- Ekström, Sven-Erik, et al.
(författare)
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A matrix-less method to approximate the spectrum and the spectral function of Toeplitz matrices with real eigenvalues
- 2022
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Ingår i: Numerical Algorithms. - : Springer Nature. - 1017-1398 .- 1572-9265. ; 89:2, s. 701-720
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Tidskriftsartikel (refereegranskat)abstract
- It is known that the generating function f of a sequence of Toeplitz matrices {Tn(f)}n may not describe the asymptotic distribution of the eigenvalues of Tn(f) if f is not real. In this paper, we assume as a working hypothesis that, if the eigenvalues of Tn(f) are real for all n, then they admit an asymptotic expansion of the same type as considered in previous works, where the first function, called the eigenvalue symbol f, appearing in this expansion is real and describes the asymptotic distribution of the eigenvalues of Tn(f). This eigenvalue symbol f is in general not known in closed form. After validating this working hypothesis through a number of numerical experiments, we propose a matrix-less algorithm in order to approximate the eigenvalue distribution function f. The proposed algorithm, which opposed to previous versions, does not need any information about neither f nor f is tested on a wide range of numerical examples; in some cases, we are even able to find the analytical expression of f. Future research directions are outlined at the end of the paper.
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| 19. |
- Ekström, Sven-Erik
(författare)
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A vertex-centered discontinuous Galerkin method for flow problems
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The understanding of flow problems, and finding their solution, has been important for most of human history, from the design of aqueducts to boats and airplanes. The use of physical miniature models and wind tunnels were, and still are, useful tools for design, but with the development of computers, an increasingly large part of the design process is assisted by computational fluid dynamics (CFD).Many industrial CFD codes have their origins in the 1980s and 1990s, when the low order finite volume method (FVM) was prevalent. Discontinuous Galerkin methods (DGM) have, since the turn of the century, been seen as the successor of these methods, since it is potentially of arbitrarily high order. In its lowest order form DGM is equivalent to FVM. However, many existing codes are not compatible with standard DGM and would need a complete rewrite to obtain the advantages of the higher order.This thesis shows how to extend existing vertex-centered and edge-based FVM codes to higher order, using a special kind of DGM discretization, which is different from the standard cell-centered type. Two model problems are examined to show the necessary data structures that need to be constructed, the order of accuracy for the method, and the use of an hp-adaptation scheme to resolve a developing shock. Then the method is further developed to solve the steady Euler equations, within the existing industrial Edge code, using acceleration techniques such as local time stepping and multigrid.With the ever increasing need for more efficient and accurate solvers and algorithms in CFD, the modified DGM presented in this thesis could be used to help and accelerate the adoption of high order methods in industry.
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| 20. |
- Ekström, Sven-Erik, et al.
(författare)
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Agglomeration multigrid for the vertex-centered dual discontinuous galerkin method
- 2010
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Ingår i: ADIGMA - a European initiative on the development of adaptive higher-order variational methods for aerospace applications. - Berlin, Heidelberg : Springer Berlin/Heidelberg. - 9783642037061 - 9783642037078 ; , s. 301-308, s. 301-308
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Bokkapitel (refereegranskat)abstract
- Agglomoration multigrid is used in many finite-volume codes for aerodynamic computations in order to reduce solution times. We show that an existing agglomeration multigrid solver developed for equations discretized with a vertex-centered, edge-based finite-volume scheme can be extended to accelerate convergence also for a vertex-centered discontinuous Galerkin method. Preliminary results for a subsonic as well as a transonic test case for the Euler equations in two space dimensions show a significant convergence acceleration for the discontinuous Galerkin equations using the agglomoration multigrid strategy.
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| 21. |
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| 24. |
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| 25. |
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| 26. |
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| 27. |
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| 28. |
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| 29. |
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| 30. |
- Ekström, Sven-Erik, et al.
(författare)
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Eigenvalues and Eigenvectors of Tau Matrices with Applications to Markov Processes and Economics
- 2021
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Ingår i: Linear Algebra and its Applications. - : Elsevier BV. - 0024-3795 .- 1873-1856. ; 627, s. 41-71
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Tidskriftsartikel (refereegranskat)abstract
- In the context of matrix displacement decomposition, Bozzo and Di Fiore introduced the so-called τe,y algebra, a generalization of the well known τ algebra. We study the properties of eigenvalues and eigenvectors of the generator Tn,e,y of the τe,y algebra. In particular, we derive the asymptotics for the outliers of Tn,e,y and the associated eigenvectors; we obtain equations for the eigenvalues of Tn,e,y, which provide also the eigenvectors of Tn,e,y; and we compute the full eigendecomposition of Tn,e,y in the specific case ey=1. We also present applications of our results in the context of queuing models, random walks, and diffusion processes, with a special attention to their implications in the study of wealth/income inequality and portfolio dynamics.
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| 31. |
- Ekström, Sven-Erik, et al.
(författare)
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Eigenvalues and Eigenvectors of Tau Matrices with Applications to Markov Processes and Economics
- 2020
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In the context of matrix displacement decomposition, Bozzo and Di Fiore introduced the so-called τ\epsilon,\phi algebra, a generalization of the more known τ algebra originally proposed by Bini and Capovani. We study the properties of eigenvalues and eigenvectors of the generator Tn,\epsilon,\phi of the τ\epsilon,\phi algebra. In particular, we derive the asymptotics for the outliers of Tn,\epsilon,\phi and the associated eigenvectors; we obtain equations for the eigenvalues of Tn,\epsilon,\phi, which provide also the eigenvectors of Tn,\epsilon,\phi; and we compute the full eigendecomposition of Tn,\epsilon,\phi in the specific case \epsilon\phi=1. We also present applications of our results in the context of queuing models, random walks, and diffusion processes, with a special attention to their implications in the study of wealth/income inequality and portfolio dynamics.
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| 32. |
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| 33. |
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| 34. |
- Ekström, Sven-Erik, et al.
(författare)
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Incorporating a Galerkin method into the existing vertex-centered edge-based finite volume solver edge
- 2010
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Ingår i: ADIGMA - a European initiative on the development of adaptive higher-order variational methods for aerospace applications. - Berlin, Heidelberg : Springer Berlin/Heidelberg. - 9783642037061 - 9783642037078 ; , s. 39-52, s. 39-52
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Bokkapitel (refereegranskat)abstract
- The discontinuous Galerkin (DG) method can be viewed as a generalization to higher orders of the finite volume method. At lowest order, the standard DG method reduces to the cell-centered finite volume method.We introduce for the Euler equations an alternative DG formulation that reduces to the vertex-centered version of the finite volume method at lowest order. The method has been successfully implemented for the Euler equations in two space dimensions, allowing a local polynomial order up to p=3 and supporting curved elements at the airfoil boundary. The implementation has been done as an extension within the existing edge-based vertex-centered finite-volume code Edge.
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| 35. |
- Ekström, Sven-Erik, 1977-
(författare)
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Matrix-Less Methods for Computing Eigenvalues of Large Structured Matrices
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- When modeling natural phenomena with linear partial differential equations, the discretized system of equations is in general represented by a matrix. To solve or analyze these systems, we are often interested in the spectral behavior of these matrices. Whenever the matrices of interest are Toeplitz, or Toeplitz-like, we can use the theory of Generalized Locally Toeplitz (GLT) sequences to study the spectrum (eigenvalues). A central concept in the theory of GLT sequences is the so-called symbol, that is, a function associated with a sequence of matrices of increasing size. When sampling the symbol and when the related matrix sequence is Hermitian (or quasi-Hermitian), we obtain an approximation of the spectrum of a matrix of a fixed size and we can therefore see its general behavior. However, the so-computed approximations of the eigenvalues are often affected by errors having magnitude of the reciprocal of the matrix size.In this thesis we develop novel methods, which we call "matrix-less" since they neither store the matrices of interest nor depend on matrix-vector products, to estimate these errors. Moreover, we exploit the structures of the considered matrices to efficiently and accurately compute the spectrum.We begin by considering the errors of the approximate eigenvalues computed by sampling the symbol on a uniform grid, and we conjecture the existence of an asymptotic expansion for these errors. We devise an algorithm to approximate the expansion by using a small number of moderately sized matrices, and we show through numerical experiments the effectiveness of the algorithm. We also show that the same algorithm works for preconditioned matrices, a result which is important in practical applications. Then, we explain how to use the approximated expansion on the whole spectrum for large matrices, whereas in earlier works its applicability was restricted only to certain matrix sizes and to a subset of the spectrum. Next, we demonstrate how to use the so-developed techniques to investigate, solve, and improve the accuracy in the eigenvalue computations for various differential problems discretized by the isogeometric analysis (IgA) method. Lastly, we discuss a class of non-monotone symbols for which we construct the sampling grid yielding exact eigenvalues and eigenvectors.To summarize, we show, both theoretically and numerically, the applicability of the presented matrix-less methods for a wide variety of problems.
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| 36. |
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| 37. |
- Jansåker, Filip, et al.
(författare)
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Examining the causal effect of type 2 diabetes on ischemic heart disease : - a longitudinal study with four measurements (1980-2017)
- 2023
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Ingår i: Diabetes Research and Clinical Practice. - : Elsevier BV. - 1872-8227 .- 0168-8227. ; 198
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: This longitudinal study examines a possible causal effect between type 2 diabetes and ischemic heart disease (IHD) by using measurements on four occasions from the Swedish Statistics on Income and Living Conditions (SILC) together with nationwide healthcare registers.METHODS: This was a longitudinal study based on a random sample of men and women (n = 2014) from the Swedish population with four measurements in the SILC every eight years. Baseline was 1980/81 and the participants were followed for up to 37 years. The mean age and age range at baseline were 36.5 and 20-59 years, respectively. The study used Marginal Structural Modeling (MSM-Cox) to account for time-varying exposures by implementing inverse probability weighting (IPTW). MSM-Cox with IPTW was compared with Cox proportional hazard modelling.RESULTS: The hazard ratio (HR) for IHD (369 cases) with 95% confidence interval (CI) in participants with type 2 diabetes (11.1%) compared to participants without type 2 diabetes (88.9%) was significantly higher (1.99; CI = 1.15 - 3.44) when using MSM-Cox with IPTW after adjustments for clinical and sociodemographic risk factors. When applying Cox proportional hazard models adjusted for the same variables, the HR was lower and non-significant at 1.34 (CI = 0.94 - 1.98).CONCLUSIONS: This longitudinal study with four measurements assessed a possible causal association between type 2 diabetes and IHD by applying MSM-Cox with IPTW. Although causality cannot be determined due to the remaining risk of residual bias, the results may help to elucidate a potential causal relationship between type 2 diabetes and IHD. Further causal studies on possible underlying mechanisms are, however, needed.
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| 38. |
- Petrén, Henrik, et al.
(författare)
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eta-meson production in proton-proton collisions at excess energies of 40 and 72 MeV
- 2010
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Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 82:5, s. 055206-
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Tidskriftsartikel (refereegranskat)abstract
- The production of eta mesons in proton-proton collisions has been studied using the WASA detector at the CELSIUS storage ring at excess energies of Q = 40 MeV and Q = 72 MeV. The eta was detected through its 2 gamma decay in a near-4 pi electromagnetic calorimeter, whereas the protons were measured by a combination of straw chambers and plastic scintillator planes in the forward hemisphere. About 6.9 x 10(4) and 9.3 x 10(4) events were found at Q = 40 MeV and Q = 72 MeV, respectively, with background contributions of less than 5%. A simple parametrization of the production cross section in terms of low partial waves was used to evaluate the acceptance corrections. Strong evidence was found for the influence of higher partial waves. The Dalitz plots show the presence of p waves in both the pp and the eta {pp} systems and the angular distributions of the eta in the center-of-mass frame suggest the influence of d-wave eta mesons.
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| 39. |
- Schönning, Karin, et al.
(författare)
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Production of eta and 3 pi mesons in the pd -> (HeX)-He-3 reaction at 1360 and 1450 MeV
- 2010
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Ingår i: European Physical Journal A. - : Springer Science and Business Media LLC. - 1434-6001 .- 1434-601X. ; 45:1, s. 11-21
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Tidskriftsartikel (refereegranskat)abstract
- The cross-sections of the pd -> He-3 eta, pd -> He-3 pi(0)pi(0)pi(0) and pd -> He-3 pi(+)pi(-)pi(0) reactions have been measured at the beam kinetic energies T-p = 1360 MeV and T-p = 1450 MeV using the CELSIUS/WASA detector setup. At both energies, the differential cross-section d sigma/d Omega of the eta meson in the pd -> He-3 eta reaction shows a strong forward-backward asymmetry in the CMS. The ratio between the pd -> He-3 pi(+)pi(-)pi(0) and pd -> He-3 pi(0)pi(0)pi(0) cross-sections has been analysed in terms of isospin amplitudes. The reconstructed invariant-mass distributions of the pi pi, He-3 pi and (3)He2 pi systems provide hints on the role of nucleon resonances in the 3 pi production process.
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