ppxscal/embedding_network huggingface dataset:
Prospects for Optical Interconnects in Distributed, Shared-Memory Organized MIMD Architectures
Authors: Edward E. E. Frietman, Ramon J. Ernst, Roy Crosbie, Masao Shimoji
Venue: The Journal of Supercomputing (1999)

The antipodes of the class of sequential computers, executing tasks with a single CPU, are the parallel computers containing large numbers of computing nodes. In the shared-memory category, each node has direct access through a switching network to a memory bank, that can be composed of a single but large or multiple but medium sized memory configurations. Opposite to the first category are the distributed memory systems, where each node is given direct access to its own local memory section. Running a program in especially the latter category requires a mechanism that gives access to multiple address spaces, that is, one for each local memory. Transfer of data can only be done from one address space to another. Along with the two categories are the physically distributed, shared-memory systems, that allow the nodes to explore a single globally shared address space. All categories, the performances of which are subject to the way the computing nodes are linked, need either a direct or a switched interconnection network for inter-node communication purposes. Linking nodes and not taking into account the prerequisite of scalability in case of exploiting large numbers of them is not realistic, especially when the applied connection scheme must provide for fast and flexible communications at a reasonable cost. Different network topologies, varying from a single shared bus to a more complex elaboration of a fully connected scheme, and with them the corresponding intricate switching protocols have been extensively explored. A different vision is introduced concerning future prospects of an optically coupled distributed, shared-memory organized multiple-instruction, multiple-data system. In each cluster, an electrical crossbar looks after the interconnections between the nodes, the various memory modules and external I/O channels. The clusters itself are optically coupled through a free space oriented data distributing system. Analogies found in the design of the Convex SPP1000 substantiate the closeness to reality of such an architecture. Subsequently to the preceding introduction also an idealized picture of the fundamental properties of an optically based, fully connected, distributed, (virtual) shared-memory architecture is outlined.
Overcoming Corner Singularities Using Multigrid Methods
Authors: Susanne C. Brenner
Venue: SIAM Journal on Numerical Analysis (1998)

We consider the Poisson equation $-\Delta u = f$ with homogeneous Dirichlet boundary condition on a two-dimensional polygonal domain $\O$. We develop a finite element multigrid method on quasi-uniform grids that obtains ${\cal{O}}(h^{m+1-\epsilon})$ convergence in the $H^1(\O)$ norm for any positive $\epsilon$ when $f \in H^m(\O)$. The cost of the method is proportional to the number of elements in the triangulation. The results of this paper can be generalized to other equations and other boundary conditions.
A Restricted Additive Schwarz Preconditioner for General Sparse Linear Systems
Authors: Xiao-Chuan Cai, Marcus Sarkis
Venue: SIAM Journal on Scientific Computing (1999)

We introduce some cheaper and faster variants of the classical additive Schwarz preconditioner (AS) for general sparse linear systems and show, by numerical examples, that the new methods are superior to AS in terms of both iteration counts and CPU time, as well as the communication cost when implemented on distributed memory computers. This is especially true for harder problems such as indefinite complex linear systems and systems of convection-diffusion equations from three-dimensional compressible flows. Both sequential and parallel results are reported.
Integral Equation Preconditioning for the Solution of Poisson's Equation on Geometrically Complex Regions
Authors: Christopher R. Anderson., Archie C. Li
Venue: SIAM Journal on Scientific Computing (1999)

This paper is concerned with the implementation and investigation of integral equation based solvers as preconditioners for finite difference discretizations of Poisson equations in geometrically complex domains. The target discretizations are those associated with "cut-out" grids. We discuss such grids and also describe a software structure which enables their rapid construction. Computational results are presented.
Bias Removal Algorithm for 2-D Equation Error AdaptiveIIR Filters
Authors: Maha Shadaydeh, Masayuki Kawamata
Venue: Multidimensional Systems and Signal Processing (1999)

This paper proposes a bias removal algorithm for equation error-based 2-D adaptive cascade IIR filters with separable denominator function. As well known, equation error-based adaptive IIR filtering algorithms have the advantages of fast convergence and unimodal mean-square-error surface. These advantages, however, come along with the drawback of biased parameter estimates in the presence of measurement noise. The adaptive filter structure in the proposed algorithm is based on the concept of backpropagating the desired signal through a cascade of the denominator vertical and horizontal sections. To handle the bias problem, the proposed algorithm uses a scaled value of the output error of each of the cascaded sections as an estimate for the measurement noise embedded in the signal part of the coefficient-update procedure of that section. Thus, while maintaining the advantages of easy stability monitoring, fast convergence, and low computational load, the effect of the measurement noise is suppressed. Input-Output stability analysis is carried out, and the constraints required to maintain stability are derived. Simulation examples are presented to support the effectiveness and the usability of the proposed bias removal algorithm in 2-D system identification and image enhancement applications.
A comparative case study of three database application development environments
Authors: Iftikhar Ahmed, Frederick H. Lochovsky
Venue: ACM SIGMIS Database (1998)

This paper describes an exploratory case study that investigates the claim that the object-oriented approach to information systems development reduces development effort and improves maintainability. Software metrics for development effort, complexity, and maintainability of three functionally similar 4GL database development environments, one objected-oriented and two traditional (relational) are compared. The results indicate that programs developed using the object-oriented environment needed fewer lines of code, had less volume, required less effort, were less complex and were more maintainable than those developed using the traditional 4GL environments.
Efficient image-based methods for rendering soft shadows
Authors: Maneesh Agrawala, Ravi Ramamoorthi, Alan Heirich, Laurent Moll
Venue: Proceedings of the 27th annual conference on Computer graphics and interactive techniques (2000)

We present two efficient imaged-based approaches for computation and display of high-quality soft shadows from area light sources. Our methods are related to shadow maps and provide the associated benefits. The computation time and memory requirements for adding soft shadows to an image depend on image size and the number of lights, not geometric scene complexity. We also show that because area light sources are localized in space, soft shadow computations are particularly well suited to imaged-based rendering techniques. Our first approach&mdash;layered attenuation maps&mdash;achieves interactive rendering rates, but limits sampling flexibility, while our second method&mdash;coherence-based raytracing of depth images&mdash;is not interactive, but removes the limitations on sampling and yields high quality images at a fraction of the cost of conventional raytracers. Combining the two algorithms allows for rapid previewing followed by efficient high-quality rendering.
An Adaptive Finite Element Method for Unsteady Convection-Dominated Flows with Stiff Source Terms
Authors: Friedrich K. Hebeker, Rolf Rannacher
Venue: SIAM Journal on Scientific Computing (1999)

We consider nonstationary convection-dominated flows with stiff source terms. As a unified approach to such problems a combined finite element method in space and time with streamline diffusion is examined numerically. It has good shock-capturing features and is implicit and L-stable. Moreover, being a Galerkin method, it admits residual-based weighted a posteriori error estimates of optimal order. We avoid the use of global stability constants by actually solving the dual problem. This in turn leads to efficient and mathematically rigorous mesh refinement strategies where the streamline diffusion parameter is used for optimizing the resulting adaptive scheme. All theoretical results are substantiated by numerical test examples. For a physical application, we turn to detonation waves at moderate relaxation times in one space dimension. The finite element method well reproduces the Chapman Jouguet speed of detonations and their wave structure. Our error estimator proves accurate and sensitive to parameters, at least on time intervals of moderate length. The adaptive scheme based on this estimator produces fairly accurate results which appear to be the best available with the present strategy. All ingredients of the numerical scheme can be extended in a natural way to higher space dimensions.
Optimizing for success: a new score function for distantly related protein sequence comparison
Authors: Maricel Kann, Richard A. Goldstein
Venue: Proceedings of the fourth annual international conference on Computational molecular biology (2000)

The exponential growth of the sequence data produced by the genome projects motivates the development of better ways of inferring structural and functional information about those newly sequenced proteins. Looking for homologies between these probe protein sequences and other protein sequences in the database has proved to be one of the most useful current techniques. This procedure, known as sequence comparison, relies on the use of an appropriate score function that discriminates homologs from non-homologs. Current score functions have difficulty identifying distantly-related homologs with low sequence similarity. As a result, there is an increased demand for a new score function that yields statistically-significant higher scores for all the pairs of homologous protein sequences including such distantly-related homologs. We present a new method for generating a score function by optimizing it for successful discrimination between homologous and unrelated proteins. The new score function (OPTIMA) out-performs other commonly used substitution matrices for the detection of distantly related protein sequences.
The Tractability of Segmentation and Scene Analysis
Authors: Martin C. Cooper
Venue: International Journal of Computer Vision (1998)

One of the fundamental problems in computer vision is the segmentation of an image into semantically meaningful regions, based only on image characteristics. A single segmentation can be determined using a linear number of evaluations of a uniformity predicate. However, minimising the number of regions is shown to be an NP-complete problem. We also show that the variational approach to segmentation, based on minimising a criterion combining the overall variance of regions and the number of regions, also gives rise to an NP-complete problem.When a library of object models is available, segmenting the image becomes a problem of scene analysis. A sufficient condition for the reconstruction of a 3D scene from a 2D image to be solvable in polynomial time is that the scene contains no cycles of mutually occluding objects and that no range information can be deduced from the image. It is known that relaxing the no cycles condition renders the problem NP-complete. We show that relaxing the no range information condition also produces an NP-complete problem.
Lower Bounds for Bayes Error Estimation
Authors: András Antos, Luc Devroye, László Györfi
Venue: IEEE Transactions on Pattern Analysis and Machine Intelligence (1999)

We give a short proof of the following result. Let $(X,Y)$ be any distribution on ${\cal N} \times \{0,1\}$, and let $(X_1,Y_1),\ldots,(X_n,Y_n)$ be an i.i.d. sample drawn from this distribution. In discrimination, the Bayes error $L^* = \inf_g {\bf P}\{g(X) \not= Y \}$ is of crucial importance. Here we show that without further conditions on the distribution of $(X,Y)$, no rate-of-convergence results can be obtained. Let $\phi_n (X_1,Y_1,\ldots,X_n,Y_n)$ be an estimate of the Bayes error, and let $\{ \phi_n(.) \}$ beasequence of such estimates. For any sequence $\{a_n\}$ of positive numbers converging to zero, a distribution of $(X,Y)$ may be found such that ${\bf E} \left\{ | L^* - \phi_n (X_1,Y_1,\ldots,X_n,Y_n) | \right\} \ge a_n$ infinitely often.
A Numerical Bifurcation Function for Homoclinic Orbits
Authors: Peter Ashwin, Zhen Mei
Venue: SIAM Journal on Numerical Analysis (1998)

We present a numerical method to locate periodic orbits near homoclinic orbits. Using a method of [X.-B. Lin, Proc. Roy. Soc. Edinburgh, 116A (1990), pp. 295--325] and solutions of the adjoint variational equation, we get a bifurcation function for periodic orbits, whose periods are asymptotic to infinity on approaching a homoclinic orbit. As a bonus, a linear predictor for continuation of the homoclinic orbit is easily available.Numerical approximation of the homoclinic orbit and the solution of the adjoint variational equation are discussed. We consider a class of methods for approximating the latter equation such that a scalar quantity is preserved. We also consider a context where the effects of continuous symmetries of equations can be incorporated.Applying the method to an ordinary differential equation on R3 studied by [E. Freire, A. Rodriguez-Luis, and E. Ponce, Phys. D, 62 (1993), pp. 230--253] we show the bifurcation function gives good agreement with path-followed solutions even down to low period. As an example application to a parabolic partial differential equation (PDE), we examine the bifurcation function for a homoclinic orbit in the Kuramoto--Sivashinsky equation.
Numerical Conformal Mapping Using Cross-Ratios and Delaunay Triangulation
Authors: Tobin A. Driscoll, Stephen A. Vavasis
Venue: SIAM Journal on Scientific Computing (1998)

We propose a new algorithm for computing the Riemann mapping of the unit disk to a polygon, also known as the Schwarz--Christoffel transformation. The new algorithm, CRDT (for cross-ratios of the Delaunay triangulation), is based on cross-ratios of the prevertices, and also on cross-ratios of quadrilaterals in a Delaunay triangulation of the polygon. The CRDT algorithm produces an accurate representation of the Riemann mapping even in the presence of arbitrary long, thin regions in the polygon, unlike any previous conformal mapping algorithm. We believe that CRDT solves all difficulties with crowding and global convergence, although these facts depend on conjectures that we have so far not been able to prove. We demonstrate convergence with computational experiments. The Riemann mapping has applications in two-dimensional potential theory and mesh generation. We demonstrate CRDT on problems in long, thin regions in which no other known algorithm can perform comparably.
Multiresolution Representation in Unstructured Meshes
Authors: Rémi Abgrall
Venue: SIAM Journal on Numerical Analysis (1998)

In this paper we describe techniques to represent data which originate from discretization of functions in unstructured meshes in terms of their local scale components. To do so we consider a nested sequence of discretization, which corresponds to increasing levels of resolution, and we define the scales as the "difference in information" between any two successive levels. We obtain data compression by eliminating scale-coefficients which are sufficiently small. This capability for data compression can be used to reduce the cost of numerical schemes by solving for the more compact representation of the numerical solution in terms of its significant scale-coefficients.
Producing Interoperable Queries for Relational and Object-OrientedDatabases
Authors: Ya-Hui Chang, Louiqa Raschid
Venue: Journal of Intelligent Information Systems (2000)

In this paper, we develop techniques to produce interoperable queries with object and relational databases. A user poses a local query in a local query language, against a local object or relational schema. We transparently produce appropriate queries with respect to a remote target object or relational schema, corresponding to some remote database which contains data relevant to the user's query. Mapping knowledge to resolve representational heterogeneities in local and remote schemas is expressed in a canonical representation, CRmapping, and is independent of the particular data model. A canonical representation CRquery is also used to resolve heterogeneities of query languages. A set of heterogeneous transformation algorithms define the appropriate transformations from the local queries to the remote queries. The use of canonical representations (CR) allows us to represent queries independent of the particular query language, and to resolve representational conflicts in a uniform manner, independent of models and query languages.
Replica Determinism and Flexible Scheduling in Hard Real-Time Dependable Systems
Authors: Stefan Poledna, Alan Burns, Andy Wellings, Peter Barrett
Venue: IEEE Transactions on Computers (2000)

Fault-tolerant real-time systems are typically based on active replication where replicated entities are required to deliver their outputs in an identical order within a given time interval. Distributed scheduling of replicated tasks, however, violates this requirement if on-line scheduling, preemptive scheduling, or scheduling of dissimilar replicated task sets is employed. This problem of inconsistent task outputs has been solved previously by coordinating the decisions of the local schedulers such that replicated tasks are executed in an identical order. Global coordination results either in an extremely high communication effort to agree on each schedule decision or in an overly restrictive execution model where on-line scheduling, arbitrary preemptions, and nonidentically replicated task sets are not allowed. To overcome these restrictions, a new method, called timed messages, is introduced. Timed messages guarantee deterministic operation by presenting consistent message versions to the replicated tasks. This approach is based on simulated common knowledge and a sparse time base. Timed messages are very effective since they neither require communication between the local scheduler nor do they restrict usage of on-line flexible scheduling, preemptions and nonidentically replicated task sets.
A whole new kind of engineering
Authors: L. B. S. Raccoon
Venue: ACM SIGSOFT Software Engineering Notes (2000)

There is a lot of momentum for software engineering to become a title act branch of engineering. A brochure from McMaster University (www.cas.mcmaster.ca/cas/undergraduate/SEbrochure.pdf, Fall 1999), reads, "At McMaster we have taken the position that software engineering is a branch of engineering and have applied well established principles of engineering education in this new specialty." And, the Texas Board of Professional Engineers is certifying software engineers as title act engineers, today. If other states follow then software engineering will become a title act branch of engineering by fiat.While I agree that software engineering resembles traditional engineering in many ways, I also believe that software engineering is a whole new kind of engineering that is equal to, parallel to, and independent of traditional engineering. I believe that if software engineers want to be licensed, they should recognize their unique reality and become licensed in a way that reflects this reality. Software engineers should be professionalized on their own terms, with their own regulatory structure. Software engineers should create a whole new kind of engineering, and not just follow the path trodden by traditional engineers.In the first section, I argue that software engineering is a real profession that stands on its own and that its culture differs substantially from that of traditional engineering. Software engineering is big: it counts nearly as many practitioners as traditional engineering; diverse: it has many areas of specialized practice; and enduring: it has grown steadily for more than fifty years. Every facet of software engineering, from technology to attitude to origins, differs from traditional engineering, which profoundly affects the culture of software engineering. Software engineering is not a branch of traditional engineering.In the second section, I argue that all-of-software-engineering-combined should resemble all-of-traditional-engineering-combined. Four kinds of traditional engineering regulation are practiced today that software engineering can emulate: unregulated, title-act, practice-act, and all-of-engineering-combined. Of these four kinds, title-act and all-of-engineering-combined are the most likely outcomes. There is a lot of momentum to regulate software engineering as a title-act branch of engineering. However, regulating software engineering like all-of-engineering-combined will give software engineers more control over their destiny, let them define their own identity and culture, wield their own power, and set their own curriculum and immigration policy.
Automated cache optimizations using CME driven diagnosis
Authors: Somnath Ghosh, Margaret Martonosi, Sharad Malik
Venue: Proceedings of the 14th international conference on Supercomputing (2000)

Demonstrating our framework on a collection of scientific loop nests, we were able to reduce an average of 84% of cache misses in the optimizable loop nests. This work lays the groundwork for handling a wide range of optimizations through further study of solution patterns in the CME solution table.
A Discontinuous Finite Element Method for Solving a Multiwell Problem
Authors: Matthias K. Gobbert, Andreas Prohl
Venue: SIAM Journal on Numerical Analysis (1999)

Many physical materials of practical relevance can attain several variants of crystalline microstructure. The appropriate energy functional is necessarily nonconvex, and the minimization of the functional becomes a challenging problem. A new numerical method based on discontinuous finite elements and a scaled energy functional is proposed. It exhibits excellent convergence behavior for the energy (second order) as well as other crucial quantities of interest for general spatial meshes, contrary to standard (non-)conforming methods. Both theoretical analyses and numerical test calculations are presented and contrasted to other current finite element methods for this problem.
Data Compression and Local Metrics for Nearest Neighbor Classification
Authors: Francesco Ricci, Paolo Avesani
Venue: IEEE Transactions on Pattern Analysis and Machine Intelligence (1999)

A local distance measure for the nearest neighbor classification rule is shown to achieve high compression rates and high accuracy on real data sets. In the approach proposed here, first, a set of prototypes is extracted during training and, then, a feedback learning algorithm is used to optimize the metric. Even if the prototypes are randomly selected, the proposed metric outperforms, both in compression rate and accuracy, common editing procedures like ICA, RNN, and PNN. Finally, when accuracy is the major concern, we show how compression can be traded for accuracy by exploiting voting techniques. That indicates how voting can be successfully integrated with instance-bases approaches, overcoming previous negative results.