10 research outputs found
Lattice-based kernel approximation and serendipitous weights for parametric PDEs in very high dimensions
We describe a fast method for solving elliptic partial differential equations
(PDEs) with uncertain coefficients using kernel interpolation at a lattice
point set. By representing the input random field of the system using the model
proposed by Kaarnioja, Kuo, and Sloan (SIAM J.~Numer.~Anal.~2020), in which a
countable number of independent random variables enter the random field as
periodic functions, it was shown by Kaarnioja, Kazashi, Kuo, Nobile, and Sloan
(Numer.~Math.~2022) that the lattice-based kernel interpolant can be
constructed for the PDE solution as a function of the stochastic variables in a
highly efficient manner using fast Fourier transform (FFT). In this work, we
discuss the connection between our model and the popular ``affine and uniform
model'' studied widely in the literature of uncertainty quantification for PDEs
with uncertain coefficients. We also propose a new class of weights entering
the construction of the kernel interpolant -- \emph{serendipitous weights} --
which dramatically improve the computational performance of the kernel
interpolant for PDE problems with uncertain coefficients, and allow us to
tackle function approximation problems up to very high dimensionalities.
Numerical experiments are presented to showcase the performance of the
serendipitous weights
The construction of good lattice rules and polynomial lattice rules
A comprehensive overview of lattice rules and polynomial lattice rules is
given for function spaces based on semi-norms. Good lattice rules and
polynomial lattice rules are defined as those obtaining worst-case errors
bounded by the optimal rate of convergence for the function space. The focus is
on algebraic rates of convergence for
and any , where is the decay of a series representation
of the integrand function. The dependence of the implied constant on the
dimension can be controlled by weights which determine the influence of the
different dimensions. Different types of weights are discussed. The
construction of good lattice rules, and polynomial lattice rules, can be done
using the same method for all ; but the case is special
from the construction point of view. For the
component-by-component construction and its fast algorithm for different
weighted function spaces is then discussed
Hot new directions for quasi-Monte Carlo research in step with applications
This article provides an overview of some interfaces between the theory of
quasi-Monte Carlo (QMC) methods and applications. We summarize three QMC
theoretical settings: first order QMC methods in the unit cube and in
, and higher order QMC methods in the unit cube. One important
feature is that their error bounds can be independent of the dimension
under appropriate conditions on the function spaces. Another important feature
is that good parameters for these QMC methods can be obtained by fast efficient
algorithms even when is large. We outline three different applications and
explain how they can tap into the different QMC theory. We also discuss three
cost saving strategies that can be combined with QMC in these applications.
Many of these recent QMC theory and methods are developed not in isolation, but
in close connection with applications
Fast approximation by periodic kernel-based lattice-point interpolation with application in uncertainty quantification
This paper deals with the kernel-based approximation of a multivariate
periodic function by interpolation at the points of an integration lattice -- a
setting that, as pointed out by Zeng, Leung, Hickernell (MCQMC2004, 2006) and
Zeng, Kritzer, Hickernell (Constr. Approx., 2009), allows fast evaluation by
fast Fourier transform, so avoiding the need for a linear solver. The main
contribution of the paper is the application to the approximation problem for
uncertainty quantification of elliptic partial differential equations, with the
diffusion coefficient given by a random field that is periodic in the
stochastic variables, in the model proposed recently by Kaarnioja, Kuo, Sloan
(SIAM J. Numer. Anal., 2020). The paper gives a full error analysis, and full
details of the construction of lattices needed to ensure a good (but inevitably
not optimal) rate of convergence and an error bound independent of dimension.
Numerical experiments support the theory.Comment: 37 pages, 5 figure
FAA Center of Excellence for Alternative Jet Fuels & Environment: Annual Technical Report 2021: For the Period October 1, 2020 - September 30, 2021: Volume 2
FAA Award Number 13-C.This report covers the period October 1, 2020, through September 30, 2021. The Center was established by the authority of FAA solicitation 13-C-AJFE-Solicitation. During that time the ASCENT team launched a new website, which can be viewed at ascent.aero. The next meeting will be held April 5-7, 2022, in Alexandria, VA
11th International Coral Reef Symposium Proceedings
A defining theme of the 11th International Coral Reef Symposium was that the news for coral reef ecosystems are far from encouraging. Climate change happens now much faster than in an ice-age transition, and coral reefs continue to suffer fever-high temperatures as well as sour ocean conditions. Corals may be falling behind, and there appears to be no special silver bullet remedy. Nevertheless, there are hopeful signs that we should not despair.
Reef ecosystems respond vigorously to protective measures and alleviation of stress. For concerned scientists, managers, conservationists, stakeholders, students, and citizens, there is a great role to play in continuing to report on the extreme threat that climate change represents to earth’s natural systems. Urgent action is needed to reduce CO2 emissions. In the interim, we can and must buy time for coral reefs through increased protection from sewage, sediment, pollutants, overfishing, development, and other stressors, all of which we know can damage coral health.
The time to act is now. The canary in the coral-coal mine is dead, but we still have time to save the miners. We need effective management rooted in solid interdisciplinary science and coupled with stakeholder buy in, working at local, regional, and international scales alongside global efforts to give reefs a chance.https://nsuworks.nova.edu/occ_icrs/1000/thumbnail.jp