Multivariate approximation by a combination of modified Taylor polynomials

摘要

We study an approximation of a multivariate function f by an operator of the form ∑i=1NT˜r[f,xi](x)φi(x), where φ1,…,φN are certain basis functions and T˜r[f,xi](x) are modified Taylor polynomials of degree r expanded at xi. The modification is such that the operator has highest degree of algebraic precision. In the univariate case, this operator was investigated by Xuli [Multi-node higher order expansions of a function, J. Approx. Theory 124 (2003) 242–253]. Special attention is given to the case where the basis functions are a partition of unity of linear precision. For this setting, we establish two types of sharp error estimates. In the two-dimensional case, we show that this operator gives access to certain classical interpolation operators of the finite element method. In the case where φ1,…,φN are multivariate Bernstein polynomials, we establish an asymptotic representation for the error as N→∞.