Visualization and animation tools may become extremely important aids in the understanding, verification, and performance tuning of parallel computations. Presently, however, the use of visualization has had only a li...
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Visualization and animation tools may become extremely important aids in the understanding, verification, and performance tuning of parallel computations. Presently, however, the use of visualization has had only a limited use for enhancing parallel computation. We hypothesize that one of the primary reasons for the limited use of visualization tools in parallel program development is the difficulty of acquiring the information necessary to drive the visual display. Our approach to this impediment focuses on integrating visualization support directly into a distributed computing system. Central to this integration is the addition of a logical clock that prevents the timestamps of events from violating causality. The implementation requires the "piggybacking" of a negligible amount of extra header information on system messages and the impact on performance is minimal. This results in a system that produces useful visualizations with no extra effort required by the applications programmer. Also integrated into the distributed system is support which simplifies the creation of programmer-defined, application-specific visualizations, unique to each new parallel program developed.
Blossoming has proven to be a useful technique for understanding and generalizing polynomial curves through the use of the polar form. This paper shows that general polar values may be used to control polynomial curve...
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Blossoming has proven to be a useful technique for understanding and generalizing polynomial curves through the use of the polar form. This paper shows that general polar values may be used to control polynomial curves when a related matrix is invertible. The inverse matrix provides a useful translation from these general blossom control points to well known ones such as those of Bezier. The special case in which the polar form can be evaluated through pairwise affine combinations is characterized, allowing the arguments of the blossom control points to be chosen in a manner akin to choosing the knot vector of a B-spline segment. The number of free parameters for specifying the blossom control points of polynomial curves is increased significantly over the B-spline case.
Particle-based flow visualization techniques are used for the investigation of huge, complex data sets from computational fluid dynamics (CFD). Particle tracing requires the interpolation of local velocity inside a di...
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Particle-based flow visualization techniques are used for the investigation of huge, complex data sets from computational fluid dynamics (CFD). Particle tracing requires the interpolation of local velocity inside a discretized data set and the numerical integration, to find succeeding spatial positions of the moving particles. More and more often, CFD-data is computed on unstructured Finite Element grids, which makes interpolation and integration difficult. One strategy is to resample the unstructured volume data to a regular one. In contrast to this, this article describes how particle tracing can be performed directly inside unstructured grids, thereby preserving the quality and size of the original data for visualization: The basic idea is to perform the integration in the computational space of the individual cells of the grid. This leads to a faster computation of the particle's new position and an easier determination of the corresponding new cell into which the particle has moved. The proposed algorithms allow an interactive investigation with real-time computation of particle trajectories of huge data sets that are organized on unstructured grids.
A method is presented for the modelling and animation of generalized cylinders with variable radius offset space curves. The boundary surface of a generalized cylinder is constructed: either as a translational sweep o...
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The surprising lack of research into one of the most common forms of human-computer interaction — command line interfaces — is noted, and reasons for this deficiency suggested. The features and inadequacies of exist...
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Fractal Brownian noise is used as a model describing the local grey level change in digital images. At edges this model does not truly reflect the reality, because edges add a deterministic component to the image whic...
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Fractal Brownian noise is used as a model describing the local grey level change in digital images. At edges this model does not truly reflect the reality, because edges add a deterministic component to the image which is not compatible with the notion of scale-independent self-similarity of fractal structures. Thus, the local degree of 'fractality' is used to differentiate edges from segment interiors and from noise. The concept is evaluated by comparing fractal edge detectors with conventional operators such as, e.g., a Sobel or Laplace operator. Results show a similar performance in a low-noise environment and superiority of the fractal operators in a high noise environment. The inclusion of the operators into an edge-based segmentation scheme revealed the same results for an application in image segmentation.< >
Fortran D and High Performance Fortran are languages designed to support efficient data-parallel programming on a variety of parallel architectures. The goal of the D Editor is to provide a tool that allows scientists...
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ISBN:
(纸本)9780818666056
Fortran D and High Performance Fortran are languages designed to support efficient data-parallel programming on a variety of parallel architectures. The goal of the D Editor is to provide a tool that allows scientists to use these languages efficiently. The D Editor combines analyses for shared memory machines and compiler optimizations for distributed memory machines. By cooperating with the underlying compiler, it can provide novel information on partitioning, parallelism, and communication based on compile time analysis at the level of the original Fortran program. The D Editor uses color coding and a collection of graphical displays to help the user to zoom in on portions of the program containing sequentialized code or expensive communication. The prototype implementation is useful for interactively displaying the results of compile time analysis; however, it has a number of shortcomings that must be addressed. Future enhancements will provide additional advice and transformation capabilities. We believe the D Editor is representative of a new generation of tools that will be needed to assist scientists to fully exploit languages such as High Performance Fortran.< >
A new deterministic quadratic parametric algorithm is introduced for curve estimation. A parametric biquadratic algorithm for surface estimation, based on the one for curve estimation is also presented. Our algorithm ...
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A new deterministic quadratic parametric algorithm is introduced for curve estimation. A parametric biquadratic algorithm for surface estimation, based on the one for curve estimation is also presented. Our algorithm does not assume that the surface to be estimated, based on a given set of data in the three-dimensional space, has a continuous first derivative, nor does it assume that the data satisfy the assumption of stationarity or the intrinsic hypothesis. The grid formed by the given data does not have to be equidistant;in other words the distance between neighboring points in the two-dimensional domain does not have to be the same. Also since the algorithm leads to parametric equations for the patches of the surface, the estimating surface does not need to be a function. Appropriate parameters are introduced in the blending functions of the parametric equations to produce tension. The algorithm does not require inversion of matrices and is faster than splines and kriging. The estimated surface passes through the given data points. Error analysis based on estimating surfaces of known functions from a sample of data and then comparing to their value, are made. A comparison with biqubic natural splines based on data generated from known functions is also given.
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