检索结果-内蒙古大学图书馆

arXiv 2024年

作者： Carlisle, David Libbrecht, Paul Schubotz, Moritz Soiffer, Neil Numerical Algorithms Group Ltd Oxford United Kingdom IU International University of Applied Science Erfurt Germany FIZ Karlsruhe Leibniz Institute for Information Infrastructure Berlin Germany Talking Cat Software Inc PortlandOR United States

MathML has been successful in improving the accessibility of mathematical notation on the web. All major screen readers support MathML to generate speech, allow navigation of the math, and generate braille. A troublesome area remains: handling ambiguous notations such as |x|. While it is possible to speak this syntactically, anecdotal evidence indicates most people prefer semantic speech such as "absolute value of x" or "determinant of x" instead of "vertical bar x vertical bar" when first hearing an expression. Several heuristics to infer semantics have improved speech, but ultimately, the author is the one who definitively knows how an expression is meant to be spoken. The W3C Math Working group is in the process of allowing authors to convey their intent in MathML markup via an intent attribute. This paper describes that work. Copyright © 2024, The Authors. All rights reserved.

关键词： Semantics

来源：评论

学校读者我要写书评

暂无评论

Performance of embedded boundary methods for CFD with complex geometry

引用

Journal of Physics: Conference Series 2008年第1期125卷 012083 (6p-012083 (6p页

作者： Trebotich, D. Van Straalen, B. Graves, D. Colella, P. Applied Numerical Algorithms Group Lawrence Berkeley National Laboratory Berkeley CA 94720 United States Center for Applied Scientific Computing Lawrence Livermore National Laboratory Livermore CA 94550 United States

In this paper, we discuss some of the issues in obtaining high performance for block-structured adaptive mesh refinement software for partial differential equations in complex geometry using embedded boundary/volume-of-fluid methods. We present the design of an adaptive embedded boundary multigrid algorithm for elliptic problems. We show examples in which this new elliptic solver scales to 1000 processors. We also apply this technology to more complex mathematical and physical algorithms for incompressible fluid dynamics and demonstrate similar scaling. © 2008 IOP Publishing Ltd.

关键词：

来源：评论

学校读者我要写书评

暂无评论

Embedded boundary algorithms and software for partial differential equations

引用

Journal of Physics: Conference Series 2008年第1期125卷 012084 (8p-012084 (8p页

作者： Colella, P. Graves, D. Ligocki, T. Trebotich, D. Van Straalen, B. Applied Numerical Algorithms Group Lawrence Berkeley National Laboratory Berkeley CA 94720 United States Center for Applied Scientific Computing Lawrence Livermore National Laboratory Livermore CA 94550 United States

In this paper, we give an overview of a set of methods being developed for solving classical PDEs in irregular geometries, or in the presence of free boundaries. In this approach, the irregular geometry is represented on a rectangular grid by specifying the intersection of each grid cell with the region on one or the other side of the boundary. This leads to a natural conservative discretization of the solution to the PDE on either side of the boundary. Stable and robust hyperbolic and linear elliptic/parabolic solvers have been designed and implemented. Example applications of this approach are shown for compressible and incompressible gas dynamics problems in complex geometries, and for surface diffusion in a cell membrane. © 2008 IOP Publishing Ltd.

关键词：

来源：评论

学校读者我要写书评

暂无评论

An integrated visualization and design toolkit for flexible prosthetic heart valves 00

An integrated visualization and design toolkit for flexible ...

引用

Proceedings of the conference on Visualization '00

作者： A. J. Fenlon T. David J. P. R. B. Walton School of Mechanical Engineering University of Leeds Leeds LS2 9JT United Kingdom The Numerical Algorithms Group Ltd Wilkinson House Jordan Hill Road Oxford OX2 8DR United Kingdom

来源：评论

学校读者我要写书评

暂无评论

Improving the flexibility and robustness of model-based derivative-free optimization solvers

arXiv

引用

arXiv 2018年

作者： Cartis, Coralia Fiala, Jan Marteau, Benjamin Roberts, Lindon Mathematical Institute University of Oxford Radcliffe Observatory Quarter Woodstock Road OxfordOX2 6GG United Kingdom Numerical Algorithms Group Wilkinson House Jordan Hill Road OxfordOX2 8DR United Kingdom Numerical Algorithms Group Wilkinson House Jordan Hill Road OxfordOX2 8DR United Kingdom Mathematical Institute University of Oxford Radcliffe Observatory Quarter Woodstock Road OxfordOX2 6GG United Kingdom

We present DFO-LS, a software package for derivative-free optimization (DFO) for nonlinear Least-Squares (LS) problems, with optional bound constraints. Inspired by the Gauss-Newton method, DFO-LS constructs simplified linear regression models for the residuals. DFO-LS allows flexible initialization for expensive problems, whereby it can begin making progress from as few as two objective evaluations. numerical results show DFO-LS can gain reasonable progress on some medium-scale problems with fewer objective evaluations than is needed for one gradient evaluation. DFO-LS has improved robustness to noise, allowing sample averaging, the construction of regression-based models, and multiple restart strategies together with an auto-detection mechanism. Our extensive numerical experimentation shows that restarting the solver when stagnation is detected is a cheap and effective mechanism for achieving robustness, with superior performance over both sampling and regression techniques. We also present our package Py-BOBYQA, a Python implementation of BOBYQA (Powell, 2009), which also implements robustness to noise strategies. Our numerical experiments show that Py-BOBYQA is comparable to or better than existing general DFO solvers for noisy problems. In our comparisons, we introduce a new adaptive measure of accuracy for the data profiles of noisy functions that strikes a balance between measuring the true and the noisy objective improvement. Copyright © 2018, The Authors. All rights reserved.

关键词： Python

来源：评论

学校读者我要写书评

暂无评论

A moving control volume approach to computing hydrodynamic forces and torques on immersed bodies

arXiv

引用

arXiv 2017年

作者： Nangia, Nishant Johansen, Hans Patankar, Neelesh A. Bhalla, Amneet Pal Singh Department of Engineering Sciences and Applied Mathematics Northwestern University EvanstonIL United States Department of Mechanical Engineering Northwestern University EvanstonIL United States Applied Numerical Algorithms Group Lawrence Berkeley National Laboratory BerkeleyCA United States

We present a moving control volume (CV) approach to computing hydrodynamic forces and torques on complex geometries. The method requires surface and volumetric integrals over a simple and regular Cartesian box that moves with an arbitrary velocity to enclose the body at all times. The moving box is aligned with Cartesian grid faces, which makes the integral evaluation straightforward in an immersed boundary (IB) framework. Discontinuous and noisy derivatives of velocity and pressure at the uid-structure interface are avoided and far-field (smooth) velocity and pressure information is used. We re-visit the approach to compute hydrodynamic forces and torques through force/torque balance equation in a Lagrangian frame that some of us took in a prior work (Bhalla et al., J Comp Phys, 2013). We prove the equivalence of the two approaches for IB methods, thanks to the use of Peskin's delta functions. Both approaches are able to suppress spurious force oscillations and are in excellent agreement, as expected theoretically. Test cases ranging from Stokes to high Reynolds number regimes are considered. We discuss regridding issues for the moving CV method in an adaptive mesh refinement (AMR) context. The proposed moving CV method is not limited to a specific IB method and can also be used, for example, with embedded boundary methods. Copyright © 2017, The Authors. All rights reserved.

关键词： Lagrange multipliers

来源：评论

学校读者我要写书评

暂无评论

A penalty method to model particle interactions in DNA-laden flows

A penalty method to model particle interactions in DNA-laden...

引用

作者： Trebotich, D. Miller, G.H. Bybee, M.D. Center for Applied Scientific Computing Lawrence Livermore National Laboratory P.O. Box 808 L-560 Livermore CA 94551 United States Department of Applied Science University of California One Shields Avenue Davis CA 95616 United States Applied Numerical Algorithms Group Lawrence Berkeley National Laboratory 1 Cyclotron Road Berkeley CA 94720 United States Department of Chemical and Biomolecular Engineering University of Illinois at Urbana-Champalgn Urbana IL 61801 United States

We present a hybrid fluid-particle algorithm to simulate flow and transport of DNA-laden fluids in microdevices. Relevant length scales in microfluidic systems range from characteristic channel sizes of millimeters to micron scale geometric variation (e.g., post arrays) to 10 nanometers for the length of a single rod in a bead-rod polymer representation of a biological material such as DNA. The method is based on a previous fluid-particle algorithm in which long molecules are represented as a chain of connected rods, but in which the physically unrealistic behavior of rod crossing occurred. We have extended this algorithm to include screened Coulombic forces between particles by implementing a Debye-Hückel potential acting between rods. In the method an unsteady incompressible Newtonian fluid is discretized with a second-order finite difference method in the interior of the Cartesian grid domain;an embedded boundary volume-of-fluid formulation is used near boundaries. The bead-rod polymer model is fully coupled to the solvent through body forces representing hydrodynamic drag and stochastic thermal fluctuations. While intra-polymer interactions are modeled by a soft potential, polymer-structure interactions are treated as perfectly elastic collisions. We demonstrate this method on flow and transport of a polymer through a post array microchannel in 2D where the polymer incorporates more realistic physical parameters of DNA, and compare to previous simulations where rods are allowed to cross. We also show that the method is capable of simulating 3D flow in a packed bed micro-column. Copyright © 2008 American Scientific Publishers All rights reserved.

关键词： Packed beds

来源：评论

学校读者我要写书评

暂无评论

Hashing embeddings of optimal dimension, with applications to linear least squares

arXiv

引用

arXiv 2021年

作者： Cartis, Coralia Fiala, Jan Shao, Zhen Mathematical Institute University of Oxford Radcliffe Observatory Quarter Woodstock Road OxfordOX2 6GG United Kingdom Numerical Algorithms Group Ltd 30 St Giles OxfordOX1 3LE United Kingdom

The aim of this paper is two-fold: firstly, to present subspace embedding properties for s-hashing sketching matrices, with s ≥ 1, that are optimal in the projection dimension m of the sketch, namely, m = O(d), where d is the dimension of the subspace. A diverse set of results are presented that address the case when the input matrix has sufficiently low coherence (thus removing the log2 d factor dependence in m, in the low-coherence result of Bourgain et al (2015) at the expense of a smaller coherence requirement);how this coherence changes with the number s of column nonzeros (allowing a scaling of √s of the coherence bound), or is reduced through suitable transformations (when considering hashed-instead of subsampled- coherence reducing transformations such as randomised Hadamard). Secondly, we apply these general hashing sketching results to the special case of Linear Least Squares (LLS), and develop Ski-LLS, a generic software package for these problems, that builds upon and improves the Blendenpik solver on dense input and the (sequential) LSRN performance on sparse problems. In addition to the hashing sketching improvements, we add suitable linear algebra tools for rank-deficient and for sparse problems that lead SkiLLS to outperform not only sketching-based routines on randomly generated input, but also state of the art direct solver SPQR and iterative code HSL on certain subsets of the sparse Florida matrix collection;namely, on least squares problems that are significantly overdetermined, or moderately sparse, or *** Codes 65K05, 93E24, 65F08, 65F10, 65F20, 65F50, 62J05 © 2021, CC BY.

关键词： Iterative methods

来源：评论

学校读者我要写书评

暂无评论

Distributed and collaborative visualization

Distributed and collaborative visualization

引用

作者： Brodlie, K.W. Duce, D.A. Gallop, J.R. Walton, J.P.R.B. Wood, J.D. School of Computing University of Leeds Leeds LS2 9JT United Kingdom Department of Computing Oxford Brookes University Oxford OX33 1HX United Kingdom BITD Rutherford Appleton Laboratory Chilton Didcot OX11 0QX United Kingdom Numerical Algorithms Group Ltd. Wilkinson House Jordan Hill Road Oxford OX2 8DR United Kingdom

Visualization is a powerful tool for analyzing data and presenting results in science, engineering and medicine. This paper reviews ways in which it can be used in distributed and/or collaborative environments. Distributed visualization addresses a number of resource allocation problems, including the location of processing close to data for the minimization of data traffic. The advent of the Grid Computing paradigm and the link to Web Services provides fresh challenges and opportunities for distributed visualization - including the close coupling of simulations and visualizations in a steering environment. Recent developments in collaboration have seen the growth of specialized facilities (such as Access Grid) which have supplemented traditional desktop video conferencing using the Internet and multicast communications. Collaboration allows multiple users - possibly at remote sites - to take part in the visualization process at levels which range from the viewing of images to the shared control of the visualization methods. In this review, we present a model framework for distributed and collaborative visualization and assess a selection of visualization systems and frameworks for their use in a distributed or collaborative environment. We also discuss some examples of enabling technology and review recent work from research projects in this field.

关键词： Computer graphics

来源：评论

学校读者我要写书评

暂无评论

Advanced 3D Poisson solvers and particle-in-cell methods for accelerator modeling

引用

Journal of Physics: Conference Series 2005年第1期16卷

作者： David B Serafini Peter McCorquodale Phillip Colella Lawrence Berkeley National Lab Applied Numerical Algorithms Group SciDAC Applied Differential Equations Center USA

We seek to improve on the conventional FFT-based algorithms for solving the Poisson equation with infinite-domain (open) boundary conditions for large problems in accelerator modeling and related areas. In particular, improvements in both accuracy and performance are possible by combining several technologies: the method of local corrections (MLC); the James algorithm; and adaptive mesh refinement (AMR). The MLC enables the parallelization (by domain decomposition) of problems with large domains and many grid points. This improves on the FFT-based Poisson solvers typically used as it doesn't require the all-to-all communication pattern that parallel 3d FFT algorithms require, which tends to be a performance bottleneck on current (and foreseeable) parallel computers. In initial tests, good scalability up to 1000 processors has been demonstrated for our new MLC solver. An essential component of our approach is a new version of the James algorithm for infinite-domain boundary conditions for the case of three dimensions. By using a simplified version of the fast multipole method in the boundary-to-boundary potential calculation, we improve on the performance of the Hockney algorithm typically used by reducing the number of grid points by a factor of 8, and the CPU costs by a factor of 3. This is particularly important for large problems where computer memory limits are a consideration. The MLC allows for the use of adaptive mesh refinement, which reduces the number of grid points and increases the accuracy in the Poisson solution. This improves on the uniform grid methods typically used in PIC codes, particularly in beam problems where the halo is large. Also, the number of particles per cell can be controlled more closely with adaptivity than with a uniform grid. To use AMR with particles is more complicated than using uniform grids. It affects depositing particles on the non-uniform grid, reassigning particles when the adaptive grid changes and maintaining the load ba

关键词：

来源：评论

学校读者我要写书评

暂无评论

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案：

请选择收藏分类：

通借通还

建议与咨询 留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案： 新增检索档案 确定 取消

请选择收藏分类： 新增自定义分类 确定 取消

通借通还

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

请选择保存的检索档案：

请选择收藏分类：