This paper deals with the robust extraction of line segments in noisy binary images. The principle is to find maximal geodesic arcs lying in the shape. A rigorous digital framework is first presented, then an efficien...
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(纸本)081941624X
This paper deals with the robust extraction of line segments in noisy binary images. The principle is to find maximal geodesic arcs lying in the shape. A rigorous digital framework is first presented, then an efficient algorithm is described and results on real data presented. Some hints for filling the gaps between disconnected arcs are finally exposed.
The evaluation of bulk specific deposit values forms an integral part of deep bed filtration modelling. As the observations in filtration experiments are generally restricted to the monitoring of headloss and filtrate...
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The evaluation of bulk specific deposit values forms an integral part of deep bed filtration modelling. As the observations in filtration experiments are generally restricted to the monitoring of headloss and filtrate concentration (in mass units), estimates of only absolute specific deposit values (m/v) are possible. In many previous studies, a term known as the ''bulk factor'' is incorporated into the modelling of the filtration process such that the product of the bulk factor with the absolute specific deposit (m/v), gives an estimate of the bulk specific deposit (v/v). In these investigations the bulk factor is treated as constant. Alternatively, other authors have obtained the variation of the bulk factor with the absolute specific deposit by using Kozeny's headloss model. Thus, it can be seen that so far the process of obtaining a particular variation of the bulk factor and its subsequent use in the modelling of a filtration process has not been adequately considered. The present study presents a novel approach based on the development of sequential decision-making algorithms. It is concluded that this approach has the advantages of being computationally more efficient and avoids the need to assume a headloss model.
Nonlinear two-point boundary-value problems (TPBVP) can be reduced to the iterative solution of a sequence of linear problems by means of quasilinearization techniques. Therefore, the efficient solution of linear prob...
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Nonlinear two-point boundary-value problems (TPBVP) can be reduced to the iterative solution of a sequence of linear problems by means of quasilinearization techniques. Therefore, the efficient solution of linear problems is the key to the efficient solution of nonlinear problems. Among the techniques available for solving linear two-point boundary-value problems, the method of particular solutions (MPS) is particularly attractive in that it employs only one differential system, the original nonhomogeneous system, albeit with different initial conditions. This feature of MPS makes it ideally suitable for implementation on parallel computers in that the following requirements are met: the computational effort is subdivided into separate tasks (particular solutions) assigned to the different processors;the tasks have nearly the same size;there is little intercommunication between the tasks. For the TPBVP, the speedup achievable is of O(n), where n is the dimension of the state vector, hence relatively modest for the differential systems of interest in trajectory optimization and guidance. This being the case, we transform the TPBVP into a multi-point boundary-value problem (MPBVP) involving m time subintervals, with m-l continuity conditions imposed at the interface of contiguous subintervals. For the MPBVP, the speedup achievable is of O(mn), hence substantially higher than that achievable for the TPBVP. It reduces to O(m) if the parallelism is implemented only in the time domain and not in the state domain. A drawback of the multi-point approach is that it requires the solution of a large linear algebraic system for the constants of the particular solutions. This drawback can be offset by exploiting the particular nature of the interface conditions: if the vector of constants for the first subinterval is known, the vector of constants for the subsequent subintervals can be obtained with linear transformations. Using decomposition techniques together with the discret
The purpose of this paper is to consider the worst-case choice for the sequential stable matching problem. We give the necessary and sufficient condition for the worst-case execution, which leads the sequential stable...
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The purpose of this paper is to consider the worst-case choice for the sequential stable matching problem. We give the necessary and sufficient condition for the worst-case execution, which leads the sequential stable matching algorithm to take the maximum number of proposals. We then point out that the probability that the worst-case execution occurs when a sequential stable matching algorithm is employed is extremely small.
Based on the notion of homotopy, a complete theory of the skeleton in digital spaces is given. We derive from it several very fast and efficient algorithms for constructing the skeleton (sequential or contour followin...
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Based on the notion of homotopy, a complete theory of the skeleton in digital spaces is given. We derive from it several very fast and efficient algorithms for constructing the skeleton (sequential or contour following algorithms. In this way we obtain easily, for all types of digital grids, all transformations which belong to the same family as the skeleton: binary or grey tone skeletons, euclidian or geodesic skeletons, minimal skeletons or perceptual graphs, conditional bisectors, etc. The properties of the resulting skeleton make it a good candidate for being the correct discretization of the skeletons in the continuous plane. Eine vollständige Theorie des digitalen Skelettes wird dargelegt, die sich auf das Homotopie Konzept stütz. Davon werden mehrere sehr schnelle gleichwertige Algorithmen für die Skelett Erzeugung abgeleitet (sequentielle oder grenzenfolgende Algorithmen). Auf diese Weise ist es einfach, alle benachbarten Transformationen zu vollziehen, und das ganz unabhängig des benutzten digitalen Gitters: euklidische oder geodesische Skelette, binäre oder grauwert Skelette, minimale Skelette oder Gabriel Graphe, bedingte Halbierungslinien, usw. Die Eigenschaften des erzeugten Skelettes sind dermassen gut, das wir die Überzeugung haben, daß es sich da um die richtige Diskretisierung des Skelettes im kontinuierlichen Raum handelt. Nous proposons ici une théorie complète du squelette digital s'appuyant sur la notion d'homotopie. Il en découle plusieurs algorithmes équivalents et très rapides de construction du squelette (algorithmes séquentiels ou de suivi de contour). Nous obtenons ainsi aisément, quelque soit la trame utilisée, toutes les transformations apparentées au squelette: squelette binaire ou à niveau de gris, euclidien ou géodésique, squelette minimal ou graphe perceptuel, bissectrices conditionnelles, etc. Les propriétés du squelette obtenu permettent de penser qu'il s'agit là de la bonne discrétisation du squelette dans le plan continu.
Numerical results are obtained on sequential and parallel versions of ABS algorithms for linear systems for both full matrices andq-band matrices. The results using the sequential algorithm on full matrices indicate t...
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Numerical results are obtained on sequential and parallel versions of ABS algorithms for linear systems for both full matrices andq-band matrices. The results using the sequential algorithm on full matrices indicate the superiority of a particular implementation of the symmetric algorithm. The condensed form of the algorithm is well suited for implementation in a parallel environment, and results obtained on the IBM 4381 system favor a synchronous implementation over the asynchronous one. Results are obtained from sequential implementations of theLU, Cholesky, and symmetric algorithms of the ABS class forq-band matrices able to reduce memory storage. A simple parallelization of do-loops for calculating components gives interesting performances.
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