Inequalities for Rational Functions

A new hyperbolic area estimate for the level sets of finite Blaschke products is presented. The following inversion of the usual Sobolev embedding theorem is proved:

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Hereris a rational function of degreenwith poles outside . This estimate implies a new inverse theorem for rational approximation of analytic functions with respect to areaL^pnorm.     

Rational Functions with Prescribed Critical Points

A rational function is the ratio of two complex polynomials in one variable without common roots. Its degree is the maximum of the degrees of the numerator and the denominator. Rational functions belong to the same class if one turns into the other by postcomposition with a linear-fractional transformation. We give an explicit formula for the number of classes having a given degree d and given multiplicities m₁,..., m_n of given n critical points, for generic positions of the critical points. This number is the multiplicity of the irreducible sl₂ representation with highest weight in the tensor product of the irreducible sl₂ representations with highest weights The classes are labeled by the orbits of critical points of a remarkable symmetric function which first appeared in the XIX century in studies of Fuchsian differential equations, and then in the XX century in the theory of KZ equations.     

Approximation of Transfer Functions of Unstable Infinite Dimensional Control Systems by Rational Interpolants with Prescribed Poles

Rational interpolants, some of the poles of which are left free, are used to approximate the transfer functions of a large class of possibly unstable infinite-dimensional control systems. The free poles are used to detect the singularities of the transfer function which are responsible for the instability of the system.     

Inequalities for Complex Rational Functions

Ukrainian Mathematical Journal - For a rational function r(z)?=?p(z)/H(z) all zeros of which are in |z|?≤?1, it is known that $$ left|r^{prime }(z)right|ge...     

一类预给极点的有理样条的构造

构造了一类特殊的有理样条,给出其表现公式及唯一性证明,并通过实例说明其优越性.     

Rational Functions with Prescribed Global and Local Minimizers

A family of multivariate rational functions is constructed. It has strong local minimizers with prescribed function values at prescribed positions. While there might be additional local minima, such minima cannot be global. A second family of multivariate rational functions is given, having prescribed global minimizers and prescribed interpolating data.     

Markov- and Bernstein-Type Inequalities for Polynomials with Restricted Coefficients

The Markov-type inequality is proved for all polynomials of degree at most n with coefficients from {-1,0,1} with an absolute constant c. Here ·[0,1] denotes the supremum norm on [0,1]. The Bernstein-type inequality is shown for every polynomial p of the form The inequality is also proved for every analytic function p on the open unit disk D that satisfies the growth condition      

On the Bernstein Inequality for Rational Functions with a Prescribed Zero

We extend some results of Giroux and Rahman (Trans. Amer. Math. Soc.193(1974), 67–98) for Bernstein-type inequalities on the unit circle for polynomials with a prescribed zero atz=1 to those for rational functions. These results improve the Bernstein-type inequalities for rational functions. The sharpness of these inequalities is also established. Our approach makes use of the Malmquist–Walsh system of orthogonal rational functions on the unit circle associated with the Lebesgue measure.     

Inequalities for the Derivatives of Rational Functions with Real Zeros

We study Turán-type inequalities for the derivatives of rational functions, whose zeros are all real and lie inside [-1,1] but whose poles are outside (-1,1), in the supremum- and L2-norms respectively. We generalize several well-known results for classical polynomials. We also obtain a sharp L2 Bernstein-type inequality for the rational system with prescribed poles.     

Bernstein-Type Approximation Processes for Vector-valued Functions

A sequence of Bernstein-type operators for vector-valued functions is provided and its uniform convergence is considered by making use of a theorem of Korovkin type under certain requirements.     

Sharp Inequalities for Rational Functions on a Circle

Mathematical Notes - For rational functions with prescribed poles lying outside the unit circle $$|z|=1$$ , sharp inequalities are established at points $$z$$ , $$|z|=1$$ . In contrast to known...     

Upper Estimates in Direct Inequalities for Bernstein-Type Operators

We obtain explicit upper estimates in direct inequalities with respect to the usual sup-norm distance for Bernstein-type operators. Our approach combines analytical and probabilistic techniques based on representations of the operators in terms of stochastic processes. We illustrate our results by considering some classical families of operators, such as Weierstrass, Szàsz, and Bernstein operators.     

Bernstein-Type Inequalities for Linear Combinations of Shifted Gaussians

Let P_n be the collection of all polynomials of degree at mostn with real coefficients. A subtle Bernstein-type extremal problemis solved by establishing the inequality for all , and m= 1, 2, ..., where c is an absolute constant and Some related inequalities and direct and inversetheorems about the approximation by elements of in L_q (R) are also discussed. 2000 Mathematics SubjectClassification 41A17 (primary).     

给定极点的有理函数插值序列的收敛性

设Γ∈Ｃ（１，α），α＞０．Ｇ是复平面上以Γ为边界的有界单连通区域．本文考虑了极点位于G外部，以广义Ｆａｂｅｒ-Ｄzｒｂａsｊａｎ有理函数的零点为插值结点的Ｌａｇｒａｎｇｅ插值有理函数序列对Ａ（G）和Ｅ^ｑ（Ｇ）（１＜ｑ＜＋∞）中函数的一致逼近和平均逼近阶的估计．     

Inequalities Concerning Rational Functions in the Complex Domain

Siberian Mathematical Journal - We establish some inequalities for the modulus of the derivative of rational functions of Bernstein and Turán type in the sup-norm on the unit disk in the...     

Elements of Prescribed Order,Prescribed Traces and Systems of Rational Functions Over Finite Fields

Let k 1 and be a system of rational functions forming a strongly linearly independent set over a finite field . Let be arbitrarily prescribed elements. We prove that for all sufficiently large extensions , there is an element of prescribed order such that is the relative trace map from onto We give some applications to BCH codes, finite field arithmetic and ordered orthogonal arrays. We also solve a question of Helleseth et~al. (Hypercubic 4 and 5-designs from Double-Error-Correcting codes, Des. Codes. Cryptgr. 28(2003). pp. 265–282) completely.classification 11T30, 11G20, 05B15     

Inequalities for Functions with Higher Monotonicities

We consider real functions on [a, b] for which some derivatives have constant sign. For these functions we obtain Popoviciu and Favard-Berwald type inequalities as well as converse Holder inequalities.     

Convergence of Rational Interpolants with Preassigned Poles

Let Ω be a domain in the extended complex plane such that ∞∈Ω . Further, let K= C / Ω and, for each n , let Q _n be a monic polynomial of degree n with all its zeros in K . This paper is concerned with whether (Q _n ) can be chosen so that, if f is any holomorphic function on Ω and P _n is the polynomial part of the Laurent expansion of Q _n f at ∞ , then (P _n /Q _n ) converges to f locally uniformly on Ω . It is shown that such a sequence (Q _n ) can be chosen if and only if either K has zero logarithmic capacity or Ω is regular. January 21, 1999. Date accepted: August 17, 1999.     

Inequalities for Cyclic Functions

The nth cyclic function is defined by

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We prove that if k is an integer with 1kn−1, then

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holds for all positive real numbers x with the best possible constantsα=1 and β= 2n-k over n.