Let $$T_n$$ be the linear Hadamard convolution operator acting over Hardy space $$H^q$$ , $$1\le q\le \infty $$ . We call a best approximation-preserving (BAP operator) if $$T_n(e_n)=e_n$$ where $$e_n(z):=z^n,$$ and $$\Vert T_n(f)\Vert _q\le E_n(f)_q$$ for all $$f\in H^q$$ $$E_n(f)_q$$ is approximation by algebraic polynomials of degree most $$n-1$$ in space. give necessary sufficient condition...

The denseness of rational functions with prescribed poles in the Hardy space and disk algebra is considered. Notations. C complex plane D unit disk fz : jzj < 1g Tunit circle fz : jzj = 1g H p Hardy space of analytic functions on D kfk 1 := supfjf(z)j : z 2 D g, the H 1 norm A(D) disk algebra of functions analytic on D and continuous on D P n set of polynomials of degree at most n

The theory of Nevanlinna-Pick and Carathéodory-Fejér interpolation for matrixand operator-valued Schur class functions on the unit disk is now well established. Recent work has produced extensions of the theory to a variety of multivariable settings, including the ball and the polydisk (both commutative and noncommutative versions), as well as a time-varying analogue. Largely independent of thi...