On some problems of interpolation by ℒ-splines

_n (D) — ,s — _n (D), _v (v=1, 2, ...,s/2) — . _m={0x ₀<x ₁<...<x _2m–1<2,x _2m =x ₀+2} , x _j +1–x _j <(4s max _v )^–1,j=0, 1, ..., 2m –1, ( ) 2- - _n,m 2m , _m . , L _q - (1q) W ( _n )={f ₂ :f ^(n–1)AC ₂ , _n (D)f 1} 2- - (s _n f), _m . , - - _n,m .

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The author expresses his gratitude to Yu. N. Subbotin for a useful discussion on the results of this paper.     

Local ℒ-splines preserving the differential operator kernel

Odd-order local ?-splines with uniform nodes are constructed. The splines preserve basis functions from the kernel of the linear differential operator ? with constant real coefficients and pairwise different roots of the characteristic polynomial. A pointwise error of approximation by the constructed splines on appropriate classes of differentiable functions is given.     

Sharp constants in one-dimensional Poincaré-type inequalities

Mathematical Notes -     

Asymptotic constants for the error of Hermite-Fejér interpolation on the unit circle

The paper deals with the rate of convergence for the Laurent polynomials of Hermite-Fejér interpolation on the unit circle with nodal system the n roots of a complex number with modulus one. The order of convergence and the asymptotic constants are obtained when we consider analytic functions on open disks and open annulus containing the unit circle.     

Sharp constants in the Paneyah–Logvinenko–Sereda theorem

We shall find some sharp constants in one type of uncertainty principle — Paneyah–Logvinenko–Sereda theorem.     

Density conditions for interpolation inA −∞

We give a necessary and sufficient density condition for a sequence {a _k} _k in the unit disk ofC to be interpolating for the classA ^−∞ of holomorphic functions with polynomial growth. The condition goes along the lines of those found by Seip for the analogous problem in Bergman spaces of the disk and by Berenstein and Li for some weighted spaces of entire functions. The result complements an earlier characterization given by Bruna and Pascuas. Partially supported by DGICYT grant PB95-0956-C02-02 and CIRIT grant 1998 SGR 00052. Also supported by a program of the Comunitat de Treball dels Pirineus.     

Cut-elimination and interpolation for Ω-logic

In 1978, Girard introduced-logic to generalize-logic. The basic category of-logic is the categoryON of ordinals. For geometric structure reasons, Girard changed the basic categoryON into the more general categoryWF of well-founded orders (1983). The logic he obtained was called-logic. Here, we extend (unpublished) results of-logic to-logic.     

Lebesgue constants of multiple de la Vallée-Poussin sums over polyhedra

One considers linear summation methods for the multiple Fourier series the multidimensional analogues of the de la Vallé-Poussin sums. The summation of the Fourier series is carried out over the homotheties of an m-dimensional starshaped polyhedron . It is shown that if has rational vertices, then the Lebesgue constants of the considered methods, with the accuracy of O((p+1)^–1. log^m–1 (n+2)) are equal to where is the Fourier transform of the function . The exact value of the principal term of the Lebesgue constant is computed in two particular cases: 1) is obtained from an m-dimensional cube by means of a linear nonsingular transformation; 2) =0. is an m-dimensional simplex.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 125, pp. 154–165, 1983.     

Coefficient Estimates for bounded Nonvanishing Functions

Let dnote the class of all functions f(z)=sum from n=0 to ∞(a_nz~n)analytic and satisfying O<|f(z)|<1 in|z|<1.Denote A_n=sup|a_n|.It is easy to prove that A_0=1 and A_1=2/e.In 1968,Krzyz provedA_2=2/e and conjectured that A_n=2/e for all n≥1 and the equality was attained only for functionse~(iα)F(e~(iβ)z~n),where F(z)=exp[(z-1)/(z+1)]=1/e+(2/e)z-(2/3e)z~3+….In 1977,Hummel,Scheinberg andZalcman proved A_3=2/e.     

An explicit cubic iteration for π

Using the theory of the cubic modular equation we have discovered a remarkably simple class of cubically convergent algebraic iterations for .     

Richardson’s iterative method for surface interpolation

Richardson’s iterative method has been used for approximating interpolating surfaces. We propose efficient modifications for tensor product surfaces that require less computational cost and storage, as well as faster convergence. Also, we consider some aspects of the triangular case together with some counter examples.     

Approximation formulas for Landauʼs constants

In this paper, we establish approximation formulas for evaluating Landau?s constants.     

Invariant tori for the cubic Szegö equation

We continue the study of the following Hamiltonian equation on the Hardy space of the circle,

$i\partial_tu=\Pi(|u|^2u),$

where Π denotes the Szegö projector. This equation can be seen as a toy model for totally non dispersive evolution equations. In a previous work, we proved that this equation admits a Lax pair, and that it is completely integrable. In this paper, we construct the action-angle variables, which reduces the explicit resolution of the equation to a diagonalisation problem. As a consequence, we solve an inverse spectral problem for Hankel operators. Moreover, we establish the stability of the corresponding invariant tori. Furthermore, from the explicit formulae, we deduce the classification of orbitally stable and unstable traveling waves.

     

Mixed problem for a cubic Schrödinger evolution equation with a cubic dissipative term

The question of the global solvability of a mixed problem for a Schrödinger evolution equation with a cubic dissipative term is considered.     

Sarason’s interpolation theorem for analytic crossed products

Saito (Math. Proc. Camb. Phil. Soc., 117, 11–20, 1995) proved Sarason’s interpolation theorem for an analytic crossed product determined by a finite von Neumann algebra. We extend this result without the assumption that the von Neumann algebra is finite.     

On interpolation for Hrmander’s algebras

We discuss some recent results on interpolation problems for weighted Hrmander’s algebras of holomorphic functions in several complex variables, and also give a sharp estimate on counting functions of interpolating varieties.     

Sharp bounds for multilinear Hausdorff operators北大核心CSCD

We give the necessary conditions of boundedness of multilinear Hausdorff operators on Lebesgue spaces and λ-central Morrey spaces, respectively, when the kernel functions are nonnegative. Meanwhile, the corresponding operator norms are worked out. ©, 2015, Chinese Academy of Sciences. All right reserved.     

Series representations for γ and other mathematical constants

We present series representations for some mathematical constants, like γ, π, log 2, ζ(3). In particular, we prove that the following representation for Euler’s constant is valid: $$ \gamma = \sum\limits_{r = 1}^\infty {\sum\limits_{s = 1}^r {\left( {\begin{array}{*{20}c} {r - 1} \\ {s - 1} \\ \end{array} } \right)( - 1)^{r - s} 2^s \left( {\frac{1} {s} + \log \frac{s} {{s + 1}}} \right)} } . $$