Let Bnf be the m-dimensional
Bernstein polynomials on a simplex or on a cube. The class of functions for which
∥Bnf − f∥ = O(n−α) is determined. That is, necessary and sufficient conditions on
the smoothness of f in the simplex or the cube and especially near their
boundaries are given so that ∥Bnf − f∥ = O(n−α). Interpolation of spaces, and in
particular the characterization of the interpolation space, is one of the tools
used.