arXiv subjects
Publications and source records attributed to Viktor Savchuk.
We calculate the exact value and find the polynomial of the best weighted polynomial approximation of kernels of the form $\frac {A+Bt}{(t^2+\lambda^2)^{s+1}}$, where $A$ and $B$ are fixed complex numbers, $\lambda>0$, $s\in {\mathbb N}$, in the mean square metric.
Approximative properties of the Taylor-Abel-Poisson linear summation me\-thod of Fourier series are considered for functions of several variables, periodic with respect to the hexagonal domain, in the integral metric. In particular, direct and inverse theorems are proved in terms of approximations of functions by the Taylor-Abel-Poisson means and $K$-functionals generated by radial derivatives. Bernstein type inequalities for $L_1$-norm of high-order radial derivatives of the Poisson kernel are also obtained.
Approximative properties of linear summation methods of Fourier series are considered in the Orlicz type spaces ${\mathcal S}_{M}$. In particular, in terms of approximations by such methods, constructive characteristics are obtained for classes of functions whose smoothness moduli do not exceed a certain majorant.
We obtain direct and inverse approximation theorems of functions of several variables by Taylor-Abel-Poisson means in the integral metrics. We also show that norms of multipliers in the spaces $L_{p,Y}(\mathbb T^d)$ are equivalent for all positive integers $d.$
We obtain direct and inverse approximation theorems of $2π$-periodic functions by Taylor--Abel--Poisson operators in the integral metric.
We describe the two sets of meromorphic univalent functions in the class $Σ$, for which the sequence of Faber polynomials $\{F_j\}_{j=1}^\infty $ have the roots with following properties respectively: $\sum_{j=1}^{n}|F_j(z_0)|=0<|F_{n+1}(z_0)|, $ $n\in\mathbb N, $ and $|F_1(z_0)|> 0=\sum_{j=2}^{\infty}|F_j(z_0)|$. We found an explicit form of Faber polynomials for such functions.