We are concerned with the numerical integration of functions from the Sobolev space
Hr,mix([0,1]d) of dominating mixed smoothness
r∈N over the
d-dimensional unit cube. In 1976, K. K. Frolov introduced a deterministic quadrature rule whose worst case error has the order
n−r(logn)(d−1)/2 with respect to the number
n of function evaluations. This is known to be optimal. 39 years later, Erich Novak and me introduced a randomized version of this algorithm using
d random dilations. We showed that its error is bounded above by a constant multiple of
n−r−1/2(logn)(d−1)/2 in expectation and by
n−r(logn)(d−1)/2 almost surely. The main term
n−r−1/2 is again optimal and it turns out that the very same algorithm is also optimal for the isotropic Sobolev space
Hs([0,1]d) of smoothness
s>d/2. We also added a random shift to this algorithm to make it unbiased. Just recently, Mario Ullrich proved that the expected error of the resulting algorithm on
Hr,mix([0,1]d) is even bounded above by
n−r−1/2. This thesis is a review of the mentioned upper bounds and their proofs.
We study a Monte Carlo algorithm that is based on a specific (randomly shifted and dilated) lattice point set. The main result of this paper is that the mean squared error for a given compactly supported, square-integrable function is bounded by
n−1/2 times the
L2-norm of the Fourier transform outside a region around the origin, where
n is the expected number of function evaluations. As corollaries we obtain the order of convergence for the Sobolev spaces
Hps with isotropic, anisotropic or mixed smoothness for all values of the parameters. This proves, in particular, that the optimal order of convergence in the latter case is
n−s−1/2 for
p≥2, which is, in contrast to the case of deterministic algorithms, independent of the dimension. This shows that Monte Carlo algorithms can improve the order by more than
n−1/2 for a whole class of practically important function classes. All results carry over to functions defined on the unit cube without boundary conditions.
Abstract The deterministic sparse grid method, also known as Smolyak’s method, is a well-established and widely used tool to tackle multivariate approximation problems, and there is a vast literature on it. Much less is known about randomized versions of the sparse grid method. In this paper we analyze randomized sparse grid algorithms, namely randomized sparse grid quadratures for multivariate integration on the
D-dimensional unit cube
[0,1)D. Let
d,s∈N be such that
D=d⋅s. The
s-dimensional building blocks of the sparse grid quadratures are based on stratified sampling for
s=1 and on scrambled
(0,m,s)-nets for
s≥2. The spaces of integrands and the error criterion we consider are Haar wavelet spaces with parameter $\alpha $ and the randomized error (i.e., the worst case root mean square error), respectively. We prove sharp (i.e., matching) upper and lower bounds for the convergence rates of the
Nth minimal errors for all possible combinations of the parameters
d and
s. Our upper error bounds still hold if we consider as spaces of integrands Sobolev spaces of mixed dominated smoothness with smoothness parameters
1/2<α<1 instead of Haar wavelet spaces.