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Aggregation Schemes (aggregation + scheme)
Selected AbstractsDesign and evaluation of inter-bandwidth broker signalingINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 8 2008Haci A. Mantar Abstract Bandwidth brokers (BBs) have been proposed for providing end-to-end quality of services (QoS) in differentiated services (Diffserv) networks. As a single entity in each domain, a BB aims at performing both intra- and inter-domain resource management on behalf of its domain. There have been plenty of BB studies for intra-domain resource management. However, how a BB can perform inter-domain resource management in a scalable and deployable manner is still an open issue. In this work, we present the design, implementation and evaluation of an inter-BB communication protocol that is used by each BB to communicate with its neighboring BBs for inter-domain QoS resource management. The proposed model uses a destination-based aggregation scheme in which reservations are aggregated as they merge through the destination region. The destination-based aggregation improves inter-domain state and signaling scalability. The protocol also performs traffic engineering to increase inter-domain resource utilization. The implementation and simulation results verify the achievements of our model. Copyright © 2008 John Wiley & Sons, Ltd. [source] Performance of algebraic multi-grid solvers based on unsmoothed and smoothed aggregation schemesINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 7 2001R. WebsterArticle first published online: 31 JUL 200 Abstract A comparison is made of the performance of two algebraic multi-grid (AMG0 and AMG1) solvers for the solution of discrete, coupled, elliptic field problems. In AMG0, the basis functions for each coarse grid/level approximation (CGA) are obtained directly by unsmoothed aggregation, an appropriate scaling being applied to each CGA to improve consistency. In AMG1 they are assembled using a smoothed aggregation with a constrained energy optimization method providing the smoothing. Although more costly, smoothed basis functions provide a better (more consistent) CGA. Thus, AMG1 might be viewed as a benchmark for the assessment of the simpler AMG0. Selected test problems for D'Arcy flow in pipe networks, Fick diffusion, plane strain elasticity and Navier,Stokes flow (in a Stokes approximation) are used in making the comparison. They are discretized on the basis of both structured and unstructured finite element meshes. The range of discrete equation sets covers both symmetric positive definite systems and systems that may be non-symmetric and/or indefinite. Both global and local mesh refinements to at least one order of resolving power are examined. Some of these include anisotropic refinements involving elements of large aspect ratio; in some hydrodynamics cases, the anisotropy is extreme, with aspect ratios exceeding two orders. As expected, AMG1 delivers typical multi-grid convergence rates, which for all practical purposes are independent of mesh bandwidth. AMG0 rates are slower. They may also be more discernibly mesh-dependent. However, for the range of mesh bandwidths examined, the overall cost effectiveness of the two solvers is remarkably similar when a full convergence to machine accuracy is demanded. Thus, the shorter solution times for AMG1 do not necessarily compensate for the extra time required for its costly grid generation. This depends on the severity of the problem and the demanded level of convergence. For problems requiring few iterations, where grid generation costs represent a significant penalty, AMG0 has the advantage. For problems requiring a large investment in iterations, AMG1 has the edge. However, for the toughest problems addressed (vector and coupled vector,scalar fields discretized exclusively using finite elements of extreme aspect ratio) AMG1 is more robust: AMG0 has failed on some of these tests. However, but for this deficiency AMG0 would be the preferred linear approximation solver for Navier,Stokes solution algorithms in view of its much lower grid generation costs. Copyright © 2001 John Wiley & Sons, Ltd. [source] Contemporaneous aggregation of GARCH processesJOURNAL OF TIME SERIES ANALYSIS, Issue 4 2007Paolo Zaffaroni Abstract., In this article, the effect of contemporaneous aggregation of heterogeneous generalized autoregressive conditionally heteroskedastic (GARCH) processes, as the cross-sectional size diverges to infinity is studied. We analyse both cases of cross-sectionally dependent and independent individual processes. The limit aggregate does not belong to the class of GARCH processes. Dynamic conditional heteroskedasticity is only preserved when the individual processes are sufficiently cross-correlated, although long memory for the limit aggregate volatility is not attainable. We also explore more general forms of cross-sectional dependence and various types of aggregation schemes. [source] On the Construction of the European Economic Sentiment Indicator,OXFORD BULLETIN OF ECONOMICS & STATISTICS, Issue 1 2010Sarah Gelper Abstract Economic sentiment surveys are carried out by all European Union member states and are often seen as early indicators for future economic developments. Based on these surveys, the European Commission constructs an aggregate European Economic Sentiment Indicator (ESI). This paper compares the ESI with more sophisticated aggregation schemes based on statistical methods: dynamic factor analysis and partial least squares. The indicator based on partial least squares clearly outperforms the other two indicators in terms of comovement with economic activity. In terms of forecast ability, the ESI, constructed in a rather ad hoc way, can compete with the other indicators. [source] | ||||||||||