This problem is so-called the optimal

approximation problem with respect to matrix equation (2) (see e.

The function

approximation problem can be stated formally as follows [5].

Special topics include simple C*-algebras, approximation properties for groups, the weak expectation property and local lifting property, weakly exact von Neumann algebras, and such applications as Herrero's

approximation problem and classification of von Neumann algebras.

The optimal

approximation Problem II occurs frequently in experimental design, see for instance [13, 14].

Problem II is the optimal

approximation problem, which occurs frequently in experimental design [18].

k)](A) that solves the ideal GMRES

approximation problem (1.

Bernstein's

approximation problem, posed in 1924, dealt with approximation by polynomials in the norm

In this paper, we investigate the least residual problem [parallel]AX - B[parallel] = min with given X,B, and associated optimal

approximation problem in the generalized Hermitian matrix set.

WIELONSKY, On a rational

approximation problem in the real Hardy space [H.

In the next section we set up the notations, and in section 3 we state the rational

approximation problem under study.

k]) is a vectorial weight, we study this

approximation problem with the Sobolev norm [W.

So, the nonconforming

approximation problem is given by: Find [[lambda].