[1] 
M. Griebel and S. Knapek.
Optimized tensorproduct approximation spaces.
Constructive Approximation, 16(4):525540, 2000. [ bib  .ps.gz 1 ] This paper is concerned with the construction of optimized grids and approximation spaces for elliptic differential and integral equations. The main result is the analysis of the approximation of the embedding of the intersection of classes of functions with bounded mixed derivatives in standard Sobolev spaces. Based on the framework of tensorproduct biorthogonal wavelet bases and stable subspace splittings, the problem is reduced to diagonal mappings between Hilbert sequence spaces. We construct operator adapted finiteelement subspaces with a lower dimension than the standard fullgrid spaces. These new approximation spaces preserve the approximation order of the standard fullgrid spaces, provided that certain additional regularity assumptions are fulfilled. The form of the approximation spaces is governed by the ratios of the smoothness exponents of the considered classes of functions. We show in which cases the so called curse of dimensionality can be broken. The theory covers elliptic boundary value problems as well as boundary integral equations.
