ppxscal/embedding_network huggingface dataset:
A Discontinuous Galerkin Finite Element Method for Hamilton--Jacobi Equations
Authors: Changqing Hu, Chi-Wang Shu
Venue: SIAM Journal on Scientific Computing (1999)

In this paper, we present a discontinuous Galerkin finite element method for solving the nonlinear Hamilton--Jacobi equations. This method is based on the Runge--Kutta discontinuous Galerkin finite element method for solving conservation laws. The method has the flexibility of treating complicated geometry by using arbitrary triangulation, can achieve high-order accuracy with a local, compact stencil, and is suited for efficient parallel implementation. One- and two-dimensional numerical examples are given to illustrate the capability of the method. At least kth order of accuracy is observed for smooth problems when kth degree polynomials are used, and derivative singularities are resolved well without oscillations, even without limiters.
Home polysomnography norms for children
Authors: Gregory Stores, Christina Crawford, Jessica Selman, Luci Wiggs
Venue: Technology and Health Care (1998)

Home polysomnography (PSG) by means of ambulatory monitoring systems has distinct advantages over sleep laboratory recordings, especially for children. However, normative data have been lacking. Norms for conventional PSG variables were compiled for 60 children age 5-16 years using the Oxford Medilog ambulatory monitoring system. Recordings were confined to a single night in view of previous demonstrations that the sleep on the first night is not significantly affected by the recording procedure. The results are presented in 5 age subgroups. Broad comparisons with published laboratory PSG norms for children of the same ages suggest that in home recordings sleep duration is longer, and slow wave sleep is much more pronounced with a commensurate reduction in stage 2 NREM sleep. That is, sleep quality and quantity appears better at home even when adaptation to the laboratory situation has been promoted. These new normative data are considered valuable for both clinical and research purposes where physiological sleep studies in children are required.
Active virtual network management protocol
Authors: Stephen F. Bush
Venue: Proceedings of the thirteenth workshop on Parallel and distributed simulation (1999)

This paper introduces a novel algorithm, the Active Virtual Network Management Protocol, for predictive network management. It explains how the Active Virtual Network Management Protocol facilitates the management of an active network by allowing future predicted state information within an active network to be available to network management algorithms. This is accomplished by coupling ideas from optimistic discrete event simulation with active networking. The optimistic discrete event simulation method used is a form of self-adjusting Time Warp. It is self-adjusting because the system adjusts for predictions which are inaccurate beyond a given tolerance. The concept of a streptichron and autoanaplasis are introduced as mechanisms which take advantage of the enhanced flexibility and intelligence of active packets. Finally, it is demonstrated that the Active Virtual Network Management Protocol is a feasible concept.
Improving interactive performance using TIPME
Authors: Yasuhiro Endo, Margo Seltzer
Venue: ACM SIGMETRICS Performance Evaluation Review (2000)

On the vast majority of today's computers, the dominant form of computation is GUI-based user interaction. In such an environment, the user's perception is the final arbiter of performance. Human-factors research shows that a user's perception of performance is affected by unexpectedly long delays. However, most performance-tuning techniques currently rely on throughput-sensitive benchmarks. While these techniques improve the average performance of the system, they do little to detect or eliminate response-time variabilities&mdash;in particular, unexpectedly long delays.We introduce a measurement infrastructure that allows us to improve user-perceived performance by helping us to identify and eliminate the causes of the unexpected long response times that users find unacceptable. We describe TIPME (The Interactive Performance Monitoring Environment), a collection of measurement tools that allowed us to quickly and easily diagnose interactive performance &ldquo;bugs&rdquo; in a mature operating system. We present two case studies that demonstrate the effectiveness of our measurement infrastructure. Each of the performance problems we identify drastically affects variability in response time in a mature system, demonstrating that current tuning techniques do not address this class of performance problems.
An Orthogonal Spline Collocation Alternating Direction Implicit Crank--Nicolson Method for Linear Parabolic Problems on Rectangles
Authors: Bernard Bialecki, Ryan I. Fernandes
Venue: SIAM Journal on Numerical Analysis (1999)

We formulate an alternating direction implicit Crank--Nicolson scheme for solving a general linear variable coefficient parabolic problem in nondivergence form on a rectangle with the solution subject to nonhomogeneous Dirichlet boundary condition. Orthogonal spline collocation with piecewise Hermite bicubics is used for spatial discretization. We show that for sufficiently small time stepsize the scheme is stable and of optimal-order accuracy in time and the H1 norm in space. We also describe an efficient implementation of the scheme and present numerical results demonstrating the accuracy and convergence rates in various norms.
Circumventing Storage Limitations in Variational Data Assimilation Studies
Authors: Juan Mario Restrepo, Gary K. Leaf, Andreas Griewank
Venue: SIAM Journal on Scientific Computing (1998)

An application of Pontryagin's maximum principle data assimilation is used to blend possibly incomplete or nonuniformly distributed spatio-temporal observational data into geophysical models. Used extensively in engineering control theory applications, data assimilation has been introduced relatively recently into meteorological forecasting, natural-resource recovery modeling, and climate dynamics. Variational data assimilation is a promising assimilation technique in which it is assumed that the optimal state of the system is an extrema of a carefully chosen cost function. Provided that an adjoint model is available, the required model gradient can be computed by integrating the model forward and its adjoint backward. The gradient is then used to extremize the cost function with a suitable iterative or conjugate gradient solver.The problem addressed in this study is the explosive growth in both on-line computer memory and remote storage requirements of computing the gradient by the forward/adjoint technique which characterizes large-scale assimilation studies. Storage limitations impose severe limitation on the size of assimilation studies, even on the largest computers. By using a recursive strategy, a schedule can be constructed that enables the forward/adjoint model runs to be performed in such a way that storage requirements can be traded for longer computational times. This generally applicable strategy enables data assimilation studies on significantly larger domains than would otherwise be possible, given the particular hardware constraints, without compromising the outcome in any way. Furthermore, it is shown that this tradeoff is indeed viable and that when the schedule is optimized, the storage and computational times grow at most logarithmically.
Iterative Substructuring Methods for Spectral Element Discretizations of Elliptic Systems I: Compressible Linear Elasticity
Authors: Luca F. Pavarino, Olof B. Widlund
Venue: SIAM Journal on Numerical Analysis (1999)

An iterative substructuring method for the system of linear elasticity in three dimensions is introduced and analyzed. The pure displacement formulation for compressible materials is discretized with the spectral element method. The resulting stiffness matrix is symmetric and positive definite. The proposed method provides a domain decomposition preconditioner constructed from local solvers for the interior of each element and for each face of the elements and a coarse, global solver related to the wire basket of the elements. As in the scalar case, the condition number of the preconditioned operator is independent of the number of spectral elements and grows as the square of the logarithm of the spectral degree.
Depth Discontinuities by Pixel-to-Pixel Stereo
Authors: Stan Birchfield, Carlo Tomasi
Venue: International Journal of Computer Vision (1999)

An algorithm to detect depth discontinuities from a stereo pair of images is presented. The algorithm matches individual pixels in corresponding scanline pairs, while allowing occluded pixels to remain unmatched, then propagates the information between scanlines by means of a fast postprocessor. The algorithm handles large untextured regions, uses a measure of pixel dissimilarity that is insensitive to image sampling, and prunes bad search nodes to increase the speed of dynamic programming. The computation is relatively fast, taking about 600 nanoseconds per pixel per disparity on a personal computer. Approximate disparity maps and precise depth discontinuities (along both horizontal and vertical boundaries) are shown for several stereo image pairs containing textured, untextured, fronto-parallel, and slanted objects in indoor and outdoor scenes.
A corpus analysis approach for automatic query expansion and its extension to multiple databases
Authors: Susan Gauch, Jianying Wang, Satya Mahesh Rachakonda
Venue: ACM Transactions on Information Systems (TOIS) (1999)

Searching online text collections can be both rewarding and frustrating. While valuable information can be found, typically many irrelevant documents are also retrieved, while many relevant ones are missed. Terminology mismatches between the user's query and document contents are a main cause of retrieval failures. Expanding a user's query with related words can improve search performances, but finding and using related words is an open problem. This research uses corpus analysis techniques to automatically discover similar words directly from the contents of the databases which are not tagged with part-of-speech labels. Using these similarities, user queries are automatically expanded, resulting in conceptual retrieval rather than requiring exact word matches between queries and documents. We are able to achieve a 7.6% improvement for TREC 5 queries and up to a 28.5% improvement on the narrow-domain Cystic Fibrosis collection. This work has been extended to multidatabase collections where each subdatabase has a collection-specific similarity matrix associated with it. If the best matrix is selected, substantial search improvements are possible. Various techniques to select the appropriate matrix for a particular query are analyzed, and a 4.8% improvement in the results is validated.
Robust Convergence of Multilevel Algorithms for Convection-Diffusion Equations
Authors: Christoph Pflaum
Venue: SIAM Journal on Numerical Analysis (1999)

A new approach is developed to analyze convergence of multilevel algorithms for convection-diffusion equations. This approach uses a multilevel recursion formula, which can be applied to a variety of nonsymmetric problems. Here, the recursion formula is applied to a robust multilevel algorithm for convection-diffusion equations with convection in the x- or y-direction. The multilevel algorithm uses semicoarsening, line relaxation, and prewavelets. The convergence rate is proved to be less than 0.18 independent of the size of the convection term and the number of unknowns. The assumptions allow the convection term to have a turning point, so that an interior layer can appear in the solution of the convection-diffusion equation. The computational cost of the multilevel cycle is about O(N log N) independent of the size of the convection term, where N is the number of unknowns. It is proved that O(log N) multilevel cycles starting from the initial guess 0 lead to an O(N-2) algebraic error with respect to the $L^\infty$ norm, independent of the size of the convection term.
Topographic Maps and Local Contrast Changes in Natural Images
Authors: Vicent Caselles, Bartomeu Coll, Jean-Michel Morel
Venue: International Journal of Computer Vision (1999)

We call &ldquo;natural&rdquo; image any photograph of an outdoor or indoor scene taken by a standard camera. We discuss the physical generation process of natural images as a combination of occlusions, transparencies and contrast changes. This description fits to the phenomenological description of Gaetano Kanizsa according to which visual perception tends to remain stable with respect to these basic operations. We define a contrast invariant presentation of the digital image, the topographic map, where the subjacent occlusion-transparency structure is put into evidence by the interplay of level lines. We prove that each topographic map represents a class of images invariant with respect to local contrast changes. Several visualization strategies of the topographic map are proposed and implemented and mathematical arguments are developed to establish stability properties of the topographic map under digitization.
H2 and $H^\infty$ Design of Sampled-Data Systems Using Lifting. Part I: General Framework and Solutions
Authors: Leonid Mirkin, Héctor P. Rotstein, Zalman J. Palmor
Venue: SIAM Journal on Control and Optimization (1999)

This paper presents a complete solution to the H2 and $H^\infty$ problems for sampled-data systems. As opposed to previous works in the area, it is assumed here that all or some of the sampling function, the discrete-time controller, and the hold function are available for design. The solution is obtained by transforming the problem to discrete time using the well-known lifting technique. It is then shown that the desired components of the sampled-data controller can be "peeled-off" from the inherently infinite-dimensional description in the lifted-domain. The procedure for doing this last step is central to the approach in this paper. Both new and revised solutions are presented in this paper. The solution to the H2 problems is completely new. The solution to the $H^\infty$ problems is presented in a unifying framework and is more transparent than the previous existing solutions in the literature. Transparency pays in the form of clearer results. In particular, a separation structure is established between the design of (sub)optimal hold and sampler.
Efficiency, Scalability, and Robustness of Parallel Multilevel Methods for Nonlinear Partial Differential Equations
Authors: Bodo Heise, Michael Jung
Venue: SIAM Journal on Scientific Computing (1998)

In this paper we compare the performance, scalability, and robustness of different parallel algorithms for the numerical solution of nonlinear boundary value problems arising in magnetic field computation and solid mechanics. These problems are discretized by using the finite element method with triangular meshes and piecewise-linear functions. The nonlinearity is handled by a nested Newton solver, and the linear systems of algebraic equations within each Newton step are solved by means of various iterative solvers, namely multigrid methods and conjugate gradient methods with preconditioners based on domain decomposition, multigrid, or BPX techniques, respectively. The basis of the implementation of all solvers is a nonoverlapping domain decomposition data structure such that they are well suited for parallel machines with MIMD architecture.
Sensitivity Analysis of Optimization Problems Under Second Order Regular Constraints
Authors: J. Frederic Bonnans, Roberto Cominetti, Alexander Shapiro
Venue: Mathematics of Operations Research (1998)

We present a perturbation theory for finite dimensional optimization problems subject to abstract constraints satisfying a second order regularity condition. This is a technical condition that is always satisfied in the case of semi-definite optimization. We derive Lipschitz and Holder expansions of approximate optimal solutions, under a directional constraint qualification hypothesis and various second order sufficient conditions that take into account the curvature of the set defining the constraints of the problem. We show how the theory applies to semi-infinite programs in which the contact set is a smooth manifold and the quadratic growth condition in the constraint space holds, and discuss the differentiability of metric projections as well as the Moreau-Yosida regularization. Finally we show how the theory applies to semi-definite optimization.
Delay-Insensitivity and Semi-Modularity
Authors: J. A. Brzozowski, H. Zhang
Venue: Formal Methods in System Design (2000)

The study of asynchronous circuit behaviors in the presence of component and wire delays has received a great deal of attention. In this paper, we consider asynchronous circuits whose components can be any non-deterministic sequential machines of the Moore type, and describe a formal model for these circuits and their behaviors under the inertial delay model.We model an asynchronous circuit C by a network N of modules with delays associated with its components and/or wires. We compute the behavior of N assuming arbitrary inertial delays in the modules, and take this behavior to be correct. We define N to be strongly delay-insensitive if its behavior remains correct in the presence of arbitrary stray delays, where correctness is defined through the notion of observational equivalence (or bisimulation), one of the strongest forms of behavioral equivalence. We introduce the notion of quasi semi-modularity, which generalizes Muller's definition of semi-modularity to non-deterministic networks. We prove that a circuit, with all the wire delays taken into account, is strongly delay-intensitive if and only if its behavior is quasi semi-modular.
Investigating and improving a COTS-based software development
Authors: M. Morisio, C. B. Seaman, A. T. Parra, V. R. Basili, S. E. Kraft, S. E. Condon
Venue: Proceedings of the 22nd international conference on Software engineering (2000)

The work described in this paper is an investigation of COTS-based software development within a particular NASA environment, with an emphasis on the processes used. Fifteen projects using a COTS-based approach were studied and their actual process was documented. This process is evaluated to identify essential differences in comparison to traditional software development. The main differences, and the activities for which projects require more guidance, are requirements definition and COTS selection, high level design, integration and testing. Starting from these empirical observations, a new process and guidelines for COTS-based development are developed and briefly presented. The new process is currently under experimentation.
Planning Electric Power Systems Under Demand Uncertainty with Different Technology Lead Times
Authors: Douglas T. Gardner, J. Scott Rogers
Venue: Management Science (1999)

Demand uncertainty is a key concern of electric utility planners. While the greater use of short lead time technologies provides one possible way to deal with this problem, it is not clear how they are best deployed. The approach taken in this paper is to examine a capacity mix model that explicitly accounts for differences in technology lead times. Key results that are obtained include the characterization of the optimal solution and the development of a new set of technology screening criteria. In practice, the "lead time order" (i.e., the set of available technologies ordered by ascending length of lead time) is typically the inverse of the so-called merit order (i.e., the set of available technologies ordered by ascending operating cost). We show that for this case, the optimal solution may be determined with relative ease. A numerical example demonstrates that some short lead time technologies screened out by standard planning methods may enter the optimal solution when differences in lead time are considered, while some long lead time technologies may leave. In addition, the optimal expected level of reliability may be greater.
On learning algorithms and balancing loads in Time Warp
Authors: Myongsu Choe, Carl Tropper
Venue: Proceedings of the thirteenth workshop on Parallel and distributed simulation (1999)

We present, in this paper, an algorithm which integrates flow control and dynamic load balancing in order to improve the performance and stability of Time Warp. The algorithm is intended for use in a distributed memory environment such as a cluster of workstations connected by a high speed switch. Our flow control algorithm makes use of stochastic learning automata and operates in the fashion of the leaky-bucket flow control algorithm used in computer networks. It regulates the flow of messages between processors continuously throughout the course of the simulation, while the dynamic load balancing algorithm is invoked only when a load imbalance is detected. Both algorithms make use of a space-time product metric and collect the requisite information via a snapshot-based GVT algorithm.We compare the performance of the flow control algorithm, the dynamic load balancing algorithm and the integrated algorithm with that of a simulation without any of these controls. We simulated large shuffle ring networks with and without hot spots and a PCS network on an SGI Origin 2000 system.Our results indicate that the flow control scheme alone succeeds in greatly reducing the number and length of rollbacks as well as the number of anti-messages, thereby increasing the number of non-rolled back messages processed per second. It results in a large reduction in the amount of memory used and outperforms the dynamic load balancing algorithm for these measures. The integrated scheme produces even better results for all of these measures and results in reduced execution times as well.
Profits and Productivity
Authors: E. Grifell-Tatjé, C. A. K. Lovell
Venue: Management Science (1999)

In this study we consider the linkage between productivity change and profit change. We develop an analytical framework in which profit change between one period and the next is decomposed into three sources: (i) a productivity change effect (which includes a technical change effect and an operating efficiency effect), (ii) an activity effect (which includes a product mix effect, a resource mix effect, and a scale effect), and (iii) a price effect. We then show how to quantify the contribution of each effect, using only observed prices and quantities of products and resources in the two periods. We illustrate our analytical decomposition of profit change with an empirical application to Spanish banking during the period 1987-1994.
Repeated Games with Endogenous Choice of Information
Authors: Janos Flesch, Andres Perea Y Monsuwe
Venue: Mathematics of Operations Research (1999)

We consider two-player repeated games with nonobservable actions (cf. Lehrer 1989). An information mechanism for a player is a function which assigns a private signal to every action-pair of the one-shot game. In this paper, we extend the model to a situation in which both players can buy an information mechanism before playing the repeated game. Within this model, we provide a characterization of the lower equilibrium payoffs in terms of the one-shot game for the case that both players choose a nontrivial information mechanism with probability one. Moreover, we construct a lower equilibrium in a repeated game in which one of the players strictly randomizes between information mechanisms. It is shown that the corresponding payoffs cannot be induced by a lower equilibrium in which players choose a particular information mechanism with probability one.