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Gang scheduling istn't worth it ... yet
(2011)Technical reportThe hardware trend toward higher core counts will likely result in a dynamic, bursty and interactive mix of parallel applications in personal and server computing. We investigate whether gang scheduling can provide performance benefits for applications in this scenario. We present a systematic study of the conditions under which gang scheduling might be better than classical general-purpose OS scheduling, and derive a set of necessary ...Report -
Multilevel Monte Carlo method with applications to stocastic partial differential equations
(2011)SAM Research ReportIn this work the approximation of Hilbert-space-valued random variables is combined with the approximation of the expectation by a multilevel Monte Carlo method. The number of samples on the different levels of the multilevel approximation are chosen such that the errors are balanced. The overall work then decreases in the optimal case to $O(h^−$$^2)$ if $h$ is the error of the approximation. The multilevel Monte Carlo method is applied ...Report -
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Multi-level Monte Carlo finite volume methods for shallow water equations with uncertain topography in multi-dimensions
(2011)SAM Research ReportThe initial data and bottom topography, used as inputs in shallow water models, are prone to uncertainty due to measurement errors. We model this uncertainty statistically in terms of random shallow water equations. We extend the Multi-Level Monte Carlo (MLMC) algorithm to numerically approximate the random shallow water equations efficiently. The MLMC algorithm is suitably modified to deal with uncertain (and possibly uncorrelated) data ...Report -
Adaptive Galerkin approximation algorithms for partial differential equations in infinite dimensions
(2011)SAM Research ReportSpace-time variational formulations of infinite-dimensional Fokker-Planck (FP) and Ornstein-Uhlenbeck (OU) equations for functions on a separable Hilbert space $H$ are developed. The well-posedness of these equations in the Hilbert space $L^2(H,μ)$ of functions on $H$, which are square-integrable with respect to a Gaussian measure $μ$ on $H$, is proved. Specifically, for the infinite-dimensional FP equation, adaptive space-time Galerkin ...Report -
Space-time variational saddle point formulations of Stokes and Navier-Stokes equations
(2011)SAM Research ReportThe instationary Stokes and Navier-Stokes equations are considered in a simultaneously space-time variational saddle point formulation, so involving both velocities ${\bf u}$ and pressure $p$. For the instationary Stokes problem, it is shown that the corresponding operator is a boundedly invertible linear mapping between $H_1$ and $H_2'$, both Hilbert spaces $H_1$ and $H_2$ being Cartesian products of (intersections of) Bochner spaces, ...Report -
Building Data Flows Using Distributed Key-Value Stores
(2011)Technical ReportSocial communication features on most of today’s largest websites require propagating the data inside the database/key-value store leading to massive data flows. In this paper we study alternative architectures to build data flows using distributed key-value stores. We compare programming model, execution model, failure model, and scalability highlighting a problem of the state-of-the-art architecture based on an external queue: non-optimal ...Report -
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