Some remarks on quasi-Chebyshev subspaces

Approximating weak Chebyshev subspaces by Chebyshev subspaces

We examine to what extent finite-dimensional spaces defined on locally compact subsets of the line and possessing various weak Chebyshev properties (involving sign changes, zeros, alternation of best approximations, and peak points) can be uniformly approximated by a sequence of spaces having related properties. r 2003 Elsevier Science (USA). All rights reserved.

ε-weakly Chebyshev subspaces and quotient spaces

WEAK CHEBYSHEV SUBSPACES AND , 4 - SUBSPACES OF C [ a , b ]

In this paper we show some very interesting properties of weak Chebyshev subspaces and use them to simplify Pinkus's characterization of Asubspaces of C[a, b]. As a consequence we obtain that if the metric projection PG from C[a, b] onto a finite-dimensional subspace G has a continuous selection and elements of G have no common zeros on (a, b), then G is an /4-subspace.

Some constructions of subspaces cyclic and quasi-cyclic codes

In this paper we construct, using GAP System for Computational Discrete Algebra, some cyclic subspace codes, specially an optimal code over the finite field F210 . Further we present a definition and an example of the q-analogous of a m-quasi-cyclic subspace code over F28 .

Remarks on Some Newton and Chebyshev-type Methods for Approximation Eigenvalues and Eigenvectors of Matrices

It is well known that the Newton and the Chebyshev methods for nonlinear systems require solving of a linear system at each iteration step. In this note we shall study two modified methods which avoid solving of linear systems by using the Schultz method to approximate inverses of Fréchet derivatives. At the same time we shall use the particularities of nonlinear systems arising from eigenprobl...