Abstract:
The paper considers the classical problem of estimating a multidimensional parameter against a background of additive Gaussian noise. The first nontrivial term of the asymptotic expansion of the minimax risk of the estimate of a parameter belonging to bounded region $G\subset\mathbf R^k$ with piecewise-smooth boundary is investigated. Its relationship to the first eigenvalue of the Dirichlet problem in $G$ for some elliptic differential operator is established. The form of the second-order asymptotically minimax estimate is given.