Mixed norm $n$-widths

Matrices and n-Widths

This paper is concerned with a collection of ideas and problems in approximation theory which lead to some solved and unsolved problems in matrix theory. As an example, consider the problem of approximating the identity matrix by matrices of fixed rank where the norm is taken to be the maximum of the absolute value of the elements of the matrix. This problem is unsolved.

Hadron widths in mixed-phase matter.

We derive classically an expression for a hadron width in a two-phase region of hadron gas and quark-gluon plasma (QGP). The presence of QGP gives hadrons larger widths than they would have in a pure hadron gas. We find that the φ width observed in a central Au+Au collision at √ s = 200 GeV/nucleon is a few MeV greater than the width in a pure hadron gas. The part of observed hadron widths due ...

About Widths of Wiener Space in the Lq-Norm

In this paper we consider average n-widths of the Wiener space C in the Lq-norm. We study two kinds of average n-widths which describe best and best linear approximation of the Wiener space over all n-dimensional subspaces. The approximation problem on spaces with Wiener measure in the L2-norm was investigated in the book of Traub et al. (1988). Papers concerned with average n-widths in Banach ...

On n-widths for Ellipti Problems

N -widths for Singularly Perturbed Problems

Kolmogorov N-widths are an approximation theory concept that, for a given problem, yields information about the optimal rate of convergence attainable by any numerical method applied to that problem. We survey sharp bounds recently obtained for the N-widths of certain singularly perturbed convection-diffusion and reaction-diffusion boundary value problems.