953 research outputs found
Research and Education in Computational Science and Engineering
Over the past two decades the field of computational science and engineering
(CSE) has penetrated both basic and applied research in academia, industry, and
laboratories to advance discovery, optimize systems, support decision-makers,
and educate the scientific and engineering workforce. Informed by centuries of
theory and experiment, CSE performs computational experiments to answer
questions that neither theory nor experiment alone is equipped to answer. CSE
provides scientists and engineers of all persuasions with algorithmic
inventions and software systems that transcend disciplines and scales. Carried
on a wave of digital technology, CSE brings the power of parallelism to bear on
troves of data. Mathematics-based advanced computing has become a prevalent
means of discovery and innovation in essentially all areas of science,
engineering, technology, and society; and the CSE community is at the core of
this transformation. However, a combination of disruptive
developments---including the architectural complexity of extreme-scale
computing, the data revolution that engulfs the planet, and the specialization
required to follow the applications to new frontiers---is redefining the scope
and reach of the CSE endeavor. This report describes the rapid expansion of CSE
and the challenges to sustaining its bold advances. The report also presents
strategies and directions for CSE research and education for the next decade.Comment: Major revision, to appear in SIAM Revie
A bibliography on parallel and vector numerical algorithms
This is a bibliography of numerical methods. It also includes a number of other references on machine architecture, programming language, and other topics of interest to scientific computing. Certain conference proceedings and anthologies which have been published in book form are listed also
MgNO: Efficient Parameterization of Linear Operators via Multigrid
In this work, we propose a concise neural operator architecture for operator
learning. Drawing an analogy with a conventional fully connected neural
network, we define the neural operator as follows: the output of the -th
neuron in a nonlinear operator layer is defined by . Here,
denotes the bounded linear operator connecting -th input
neuron to -th output neuron, and the bias takes the form
of a function rather than a scalar. Given its new universal approximation
property, the efficient parameterization of the bounded linear operators
between two neurons (Banach spaces) plays a critical role. As a result, we
introduce MgNO, utilizing multigrid structures to parameterize these linear
operators between neurons. This approach offers both mathematical rigor and
practical expressivity. Additionally, MgNO obviates the need for conventional
lifting and projecting operators typically required in previous neural
operators. Moreover, it seamlessly accommodates diverse boundary conditions.
Our empirical observations reveal that MgNO exhibits superior ease of training
compared to other CNN-based models, while also displaying a reduced
susceptibility to overfitting when contrasted with spectral-type neural
operators. We demonstrate the efficiency and accuracy of our method with
consistently state-of-the-art performance on different types of partial
differential equations (PDEs)
Symbol Based Convergence Analysis in Block Multigrid Methods with applications for Stokes problems
The main focus of this paper is the study of efficient multigrid methods for
large linear system with a particular saddle-point structure. In particular, we
propose a symbol based convergence analysis for problems that have a hidden
block Toeplitz structure. Then, they can be investigated focusing on the
properties of the associated generating function , which
consequently is a matrix-valued function with dimension depending on the block
of the problem. As numerical tests we focus on the matrix sequence stemming
from the finite element approximation of the Stokes equation. We show the
efficiency of the methods studying the hidden block structure of
the obtained matrix sequence proposing an efficient algebraic multigrid method
with convergence rate independent of the matrix size. Moreover, we present
several numerical tests comparing the results with different known strategies
Spectral features of matrix-sequences, GLT, symbol, and application in preconditioning Krylov methods, image deblurring, and multigrid algorithms.
The final purpose of any scientific discipline can be regarded as the solution of real-world problems. With this aim, a mathematical modeling of the considered phenomenon is often compulsory. Closed-form solutions of the arising functional equations are usually not available and numerical discretization techniques are required. In this setting, the discretization of an infinite-dimensional linear equation via some linear approximation method, leads to a sequence of linear systems of increasing dimension whose coefficient matrices could inherit a structure from the continuous problem. For instance, the numerical approximation by local methods of constant or nonconstant coefficients systems of Partial Differential Equations (PDEs) over multidimensional domains, gives rise to multilevel block Toeplitz or to Generalized Locally Toeplitz (GLT) sequences, respectively. In the context of structured matrices, the convergence properties of iterative methods, like multigrid or preconditioned Krylov techniques, are strictly related to the notion of symbol, a function whose role relies in describing the asymptotical distribution of the spectrum.
This thesis can be seen as a byproduct of the combined use of powerful tools like symbol, spectral distribution, and GLT, when dealing with the numerical solution of structured linear systems. We approach such an issue both from a theoretical and practical viewpoint. On the one hand, we enlarge some known spectral distribution tools by proving the eigenvalue distribution of matrix-sequences obtained as combination of some algebraic operations on multilevel block Toeplitz matrices. On the other hand, we take advantage of the obtained results for designing efficient preconditioning techniques. Moreover, we focus on the numerical solution of structured linear systems coming from the following applications: image deblurring, fractional diffusion equations, and coupled PDEs. A spectral analysis of the arising structured sequences allows us either to study the convergence and predict the behavior of preconditioned Krylov and multigrid methods applied to the coefficient matrices, or to design effective preconditioners and multigrid solvers for the associated linear systems
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