11,941 research outputs found
A general framework for the rigorous computation of invariant densities and the coarse-fine strategy
In this paper we present a general, axiomatical framework for the rigorous
approximation of invariant densities and other important statistical features
of dynamics. We approximate the system trough a finite element reduction, by
composing the associated transfer operator with a suitable finite dimensional
projection (a discretization scheme) as in the well-known Ulam method.
We introduce a general framework based on a list of properties (of the system
and of the projection) that need to be verified so that we can take advantage
of a so-called ``coarse-fine'' strategy. This strategy is a novel method in
which we exploit information coming from a coarser approximation of the system
to get useful information on a finer approximation, speeding up the
computation. This coarse-fine strategy allows a precise estimation of invariant
densities and also allows to estimate rigorously the speed of mixing of the
system by the speed of mixing of a coarse approximation of it, which can easily
be estimated by the computer.
The estimates obtained here are rigourous, i.e., they come with exact error
bounds that are guaranteed to hold and take into account both the
discretiazation and the approximations induced by finite-precision arithmetic.
We apply this framework to several discretization schemes and examples of
invariant density computation from previous works, obtaining a remarkable
reduction in computation time.
We have implemented the numerical methods described here in the Julia
programming language, and released our implementation publicly as a Julia
package
Goal-oriented h-adaptivity for the Helmholtz equation: error estimates, local indicators and refinement strategies
The final publication is available at Springer via http://dx.doi.org/10.1007/s00466-010-0557-2This paper introduces a new goal-oriented adaptive technique based on a simple and effective post-process of the finite element approximations. The goal-oriented character of the estimate is achieved by analyzing both the direct problem and an auxiliary problem, denoted as adjoint or dual problem, which is related to the quantity of interest. Thus, the error estimation technique proposed in this paper would fall into the category of recovery-type explicit residual a posteriori error estimates. The procedure is valid for general linear quantities of interest and it is also extended to non-linear ones. The numerical examples demonstrate the efficiency of the proposed approach and discuss: (1) different error representations, (2) assessment of the dispersion error, and (3) different remeshing criteria.Peer ReviewedPostprint (author's final draft
Sparse approximation of multilinear problems with applications to kernel-based methods in UQ
We provide a framework for the sparse approximation of multilinear problems
and show that several problems in uncertainty quantification fit within this
framework. In these problems, the value of a multilinear map has to be
approximated using approximations of different accuracy and computational work
of the arguments of this map. We propose and analyze a generalized version of
Smolyak's algorithm, which provides sparse approximation formulas with
convergence rates that mitigate the curse of dimension that appears in
multilinear approximation problems with a large number of arguments. We apply
the general framework to response surface approximation and optimization under
uncertainty for parametric partial differential equations using kernel-based
approximation. The theoretical results are supplemented by numerical
experiments
Fully computable a posteriori error bounds for hybridizable discontinuous Galerkin finite element approximations
We derive a posteriori error estimates for the hybridizable discontinuous
Galerkin (HDG) methods, including both the primal and mixed formulations, for
the approximation of a linear second-order elliptic problem on conforming
simplicial meshes in two and three dimensions.
We obtain fully computable, constant free, a posteriori error bounds on the
broken energy seminorm and the HDG energy (semi)norm of the error. The
estimators are also shown to provide local lower bounds for the HDG energy
(semi)norm of the error up to a constant and a higher-order data oscillation
term. For the primal HDG methods and mixed HDG methods with an appropriate
choice of stabilization parameter, the estimators are also shown to provide a
lower bound for the broken energy seminorm of the error up to a constant and a
higher-order data oscillation term. Numerical examples are given illustrating
the theoretical results
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