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Approximation complexity of tensor product-type random fields with heavy spectrum
Authors:A A Khartov
Institution:1. St. Petersburg State University, St. Petersburg, Russia
Abstract:We consider a sequence of Gaussian tensor product-type random fields ></img>                                </span>                              </span>, where <span class= ></img>                              </span> and <span class= ></img>                              </span> are all positive eigenvalues and eigenfunctions of the covariance operator of the process <em>X</em>                              <sub>1</sub>, <span class= ></img>                              </span> are standard Gaussian random variables, and <span class= ></img>                              </span> is a subset of positive integers. For each <em>d</em> ∈ ?, the sample paths of <em>X</em>                              <sub>                                <em>d</em>                              </sub> almost surely belong to <em>L</em>                              <sub>2</sub>(0, 1]<sup>                                <em>d</em>                              </sup>) with norm ∥·∥<sub>2,<em>d</em>                              </sub>. The tuples <span class= ></img>                              </span>, are the eigenpairs of the covariance operator of <em>X</em>                              <sub>                                <em>d</em>                              </sub>. We approximate the random fields <em>X</em>                              <sub>                                <em>d</em>                              </sub>, <em>d</em> ∈ <span class= ></img>                              </span>, by the finite sums <em>X</em>                              <span class= d (n) corresponding to the n maximal eigenvalues λ k , ></img>                              </span>.                            We investigate the logarithmic asymptotics of the average approximation complexity <span class= $n_d^{pr} (\varepsilon ,\delta ): = \min \left\{ {n \in \mathbb{N}:\mathbb{P}(\left\| {X_d - X_d^{(n)} } \right\|_{2,d}^2 > \varepsilon ^2 \mathbb{E}\left\| {X_d } \right\|_{2,d}^2 ) \leqslant \delta } \right\},$ and the probabilistic approximation complexity $n_d^{avg} (\varepsilon ): = \min \left\{ {n \in \mathbb{N}:\mathbb{E}\left\| {X_d - X_d^{(n)} } \right\|_{2,d}^2 \leqslant \varepsilon ^2 \mathbb{E}\left\| {X_d } \right\|_{2,d}^2 } \right\}$ , as the parametric dimension d → ∞ the error threshold ? ∈ (0, 1) is fixed, and the confidence level δ = δ(d, ?) is allowed to approach zero. Supplementing recent results of M.A. Lifshits and E.V. Tulyakova, we consider the case where the sequence ></img>                              </span> decreases regularly and sufficiently slowly to zero, which has not been previously studied.</td>
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