Simple proof of a theorem on removable singularities of analytic functions satisfying a Lipschitz condition

Let E be a compact subset of the complex plane ?, having positive planar Lebesgue measure. Then there exists a nonconstant function f, analytic in the domain ? É, satisfying the Lipschitz condition In this note there is given a simple proof of the theorem of N. X. Uy, formulated above. It is also proved that each bounded measurable function α, defined on the set E, can be revised on a set of small Lebesgue measure so that for the function ? obtained the Cauchy integral satisfies condition (1).     

Algebraic-polynomial approximation of functions satisfying a Lipschitz condition

For functionsf(x) ε KH^(α) [satisfying the Lipschitz condition of order α (0 < α < 1) with constant K on [?1, 1], the existence is proved of a sequence P_n (f; x) of algebraic polynomials of degree n = 1, 2,..., such that $$|f(x) - P_{n - 1} (f;x)| \leqslant \mathop {\sup }\limits_{f \in KH^{(\alpha )} } E_n (f)[(1 - x^2 )^{a/2} + o(1)],$$ when n → ∞, uniformly for x ε [?1, 1], where E_n(f) is the best approximation off(x) by polynomials of degree not higher than n.     

On certain classes of analytic functions

In this paper we introduce some new classes of analytic functions which generalise several known sequence spaces and function spaces studied by Simons, Maddox, Srivastava and others. We establish some inclusion relations, topological results and give the characterisation of continuous linear functionals for these spaces. Our results include the corresponding results of Simons, Maddox and others.     

Nuclearity of the operators of embedding of certain classes of analytic functions in weighted spaces

Translated from Matematicheskie Zametki, Vol. 43, No. 6, pp. 794–807, June, 1988.     

The Gelfand and Bernsteinn-widths of some classes of analytic functions

This paper contains generalizations of a well-known theorem of Ismagilov on Kolmogorovn-widths in a Hilbert space for Bernstein and Gelfandn-widths. Some examples are considered. Bibliography: 10 titles. Translated fromZapiski Nauchnykh Seminarov POMI, Vol. 217, 1994, pp. 112–129.     

Removable singularities for analytic functions in BMO and locally Lipschitz spaces

In this paper we study removable singularities for holomorphic functions such that sup_z|f⁽ⁿ⁾(z)|dist(z,)^s<. Spaces of this type include spaces of holomorphic functions in Campanato classes, BMO and locally Lipschitz classes. Dolzhenko (1963), Král (1976) and Nguyen (1979) characterized removable singularities for some of these spaces. However, they used a different removability concept than in this paper. They assumed the functions to belong to the function space on and be holomorphic on \ E, whereas we only assume that the functions belong to the function space on \ E, and are holomorphic there. Koskela (1993) obtained some results for our type of removability, in particular he showed the usefulness of the Minkowski dimension. Kaufman (1982) obtained some results for s=0.In this paper we obtain a number of examples with certain important properties. Similar examples have earlier been obtained for Hardy H^p classes and weighted Bergman spaces, mainly by the author. Because of the similarities in these three cases, an axiomatic approach is used to obtain some results that hold in all three cases with the same proofs. Supported by the Swedish Research Council and Gustaf Sigurd Magnusons fund of the Royal Swedish Academy of Sciences.Mathematics Subject Classification (2000):30B40, 30D45, 30D55, 46E15.     

The nevanlinna factorization in certain classes of analytic functions

It is announced that in the classes H _n ^p , 0 pz+, 0 <l/.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 126, pp. 205–207, 1983.     

Error estimates of cubature formulas exact for Haar polynomials in classes of two-variable functions satisfying a general Lipschitz condition

Upper error estimates are obtained for cubature formulas with the Haar d-property in the classes Lip(L ₁, L ₂) of two-variable functions satisfying a general Lipschitz condition. It is shown that the error of minimal cubature formulas possessing the Haar d-property have the best order of convergence to zero in the indicated classes.     

The space of bounded analytic functions and weighted Bergman spaces

In this paper, we construct a class of weighted Bergman spaces such that they can generate $H^{\infty }$ in the sense of Möbius invariance. $H^{\infty }$ is also equal to the intersection of these spaces. Applying the relation between $H^{\infty }$ and these spaces, we show that the characterization via higher order derivatives does not hold for some of these weighted Bergman spaces.     

Zeros ofA p functions and related classes of analytic functions

The functionf(z), analytic in the unit disc, is inA ^p if \(\int {\int {_{\left| z \right|< 1} \left| {f(z)} \right|^p dxdy< \infty } } \) . A necessary condition on the moduli of the zeros ofA ^p functions is shown to be best possible. The functionf(z) belongs toB ^p if \(\int {\int {_{\left| z \right|< 1} \log ^ + \left| {f(z)} \right|)^p } } \) . Let {z _n } be the zero set of aB ^p function. A necessary condition on |z _n | is obtained, which, in particular, implies that Σ(1?|z _n |)^1+(1/p)+g <∞ for all ε>0 (p≧1). A condition on the Taylor coefficients off is obtained, which is sufficient for inclusion off inB ^p. This in turn shows that the necessary condition on |z _n | is essentially the best possible. Another consequence is that, forq≧1,p<q, there exists aB ^p zero set which is not aB ^q zero set.     

Diameters of certain classes of analytic functions

Exact values have been found, for the diameters in the sense of Kolmogorov of certain classes of functions with a Hardy metric, analytic in the unit circle, whose boundary values admit of a representation by a convolution or the averaged modulus of smoothness of their boundary values is majorized by a given function. In passing, certain extremal properties of trigonometric polynomials are established.Translated from Matematicheskie Zametki, Vol. 22, No. 2, pp. 285–295, August, 1977.     

Factorization for non-nevanlinna classes of analytic functions

A generalization of the Blaschke product is constructed. This product enables one to factor out the zeros of the members of certain non-Nevanlinna classes of functions analytic in the unit disc, so that the remaining (non-vanishing) functions still belong to the same class. This is done for the classesA ⁻ⁿ (0<n<∞) andB ⁻ⁿ (0<n<2) defined as follows:f ∈A ⁻ⁿ iff |f(z)|≦C _f (1−|z|)⁻ⁿ ,f ∈B ⁻ⁿ iff |f(z)|≦exp {C _f (1−|z|)⁻ⁿ }, whereC _f depends onf.