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Direct solution of the chemical master equation using quantized tensor trains
(2013)SAM Research ReportThe Chemical Master Equation (CME) is a cornerstone of stochastic analysis and simulation of models of biochemical reaction networks. Yet direct solutions of the CME have remained elusive. Although several approaches overcome the infinite dimensional nature of the CME through projections or other means, a common feature of proposed approaches is their susceptibility to the curse of dimensionality, i.e. the exponential growth in memory and ...Report -
hp FEM for Reaction-Diffusion Equations. I: Robust Exponential Convergence
(1997)SAM Research ReportA singularly perturbed reaction-diffusion equation in two dimensions is considered. We assume analyticity of the input data, i.e., the boundary of the domain is an analytic curve and the right hand side is analytic. We show that the hp version of the finite element method leads to robust exponential convergence provided that one layer of needle elements of width $O(p \varepsilon)$ is inserted near the domain boundary, that is, the rate ...Report -
Multilevel Monte-Carlo front-tracking for random scalar conservation laws
(2012)SAM Research ReportWe consider random scalar hyperbolic conservation laws (RSCLs) in spatial dimension $d\ge 1$ with bounded random flux functions which are $\mathbb{P}$-a.s. Lipschitz continuous with respect to the state variable, for which there exists a unique random entropy solution (i.e., a measurable mapping from the probability space into $C(0,T;L^1(\mathbb{R}^d))$ with finite second moments). We present a convergence analysis of a Multi-Level ...Report -
Approximation by harmonic polynomials in star-shaped domains and exponential convergence of Trefftz hp-DGFEM
(2012)SAM Research ReportWe study the approximation of harmonic functions by means of harmonic polynomials in twodimensional, bounded, star-shaped domains. Assuming that the functions possess analytic extensions to a $\delta$-neighbourhood of the domain, we prove exponential convergence of the approximation error with respect to the degree of the approximating harmonic polynomial. All the constants appearing in the bounds are explicit and depend only on the ...Report -
Sparse Twisted Tensor Frame Discretization of Parametric Transport Operators
(2011)SAM Research ReportWe propose a novel family of frame discretizations for linear, high-dimensional parametric transport operators. Our approach is based on a least squares formulation in the phase space associated with the transport equation and by subsequent Galerkin discretization with a novel, sparse tensor product frame construction in the possibly high-dimensional phase space. The proposed twisted tensor product frame construction exploits invariance ...Report -
Two-Scale FEM for Homogenization Problems
(2001)SAM Research ReportThe convergence of a two-scale FEM for elliptic problems in divergence form with coefficients and geometries oscillating at length scale \e << 1 is analyzed. Full elliptic regularity independent of \e is shown when the solution is viewed as mapping from the slow into the fast scale. Two-scale FE spaces which are able to resolve the \e scale of the solution with work independent of \e and without analytical homogenization are introduced. ...Report -
Sparse adaptive Taylor approximation algorithms for parametric and stochastic elliptic PDEs
(2011)Research ReportsThe numerical approximation of parametric partial differential equations is a computational challenge, in particular when the number of involved parameter is large. This paper considers a model class of second order, linear, parametric, elliptic PDEs on a bounded domain D with diffusion coefficients depending on the parameters in an affine manner. For such models, it was shown in [11, 12] that under very weak assumptions on the diffusion ...Report -
hp FEM for Reaction-Diffusion Equations. II: Regularity Theory
(1997)SAM Research ReportA singularly perturbed reaction-diffusion equation in two dimensions is considered. We assume analyticity of the input data, i.e., the boundary of the domain is an analytic curve, the boundary data are analytic, and the right hand side is analytic. We give asymptotic expansions of the solution and new error bounds that are uniform in the perturbation parameter as well as in the expansion order. Additionally, we provide growth estimates ...Report -
Mixed hp-DGFEM for incompressible flows III: Pressure stabilization
(2002)SAM Research ReportWe consider stabilized mixed hp-discontinuous Galerkin methods for the discretization of the Stokes problem in three-dimensional polyhedral domains. The methods are stabilized with a term penalizing the pressure jumps. For this approach it is shown that IQk-IQk and IQk-IQk-1 elements satisfy a generalized inf-sup condition on geometric edge and boundary layer meshes that are refined anisotropically and non quasi-uniformly towards faces, ...Report -
Mixed hp-DGFEM for incompressible flows II: Geometric edge meshes
(2002)SAM Research ReportWe consider the Stokes problem in three-dimensional polyhedral domains discretized on hexahedral meshes with hp-discontinuous Galerkin finite elements of type IQk for the velocity and IQk-1 for the pressure. We prove that these elements are inf-sup stable on geometric edge meshes that are refined anisotropically and non quasi-uniformly towards edges and corners. The discrete inf-sup constant is shown to be independent of the aspect ratio ...Report