A uniqueness theorem for curves in E3-trigonometric polynomials

Translated from Ukrainskii Geometricheskii Sbornik, No. 32, pp. 3–10, 1989.     

Chapter 4:algebraic sets,polynomials, and other functions

Let T be a linear operator on the vector space V ofn×n matrices over a field F. We discuss two types of problems in this chapter. First, what can we say about T if we assume that T maps a given algebraic set such as the special linear group into itself? Second, let p(x) be a polynomial function (such as det) on V into F. What can we say about T if Tpreserves p(x), i.e. p(T(X)) = p(X) for all X in V?     

Chapter 4:algebraic sets, polynomials, and other functions

Let T be a linear operator on the vector space V ofn×n matrices over a field F. We discuss two types of problems in this chapter. First, what can we say about T if we assume that T maps a given algebraic set such as the special linear group into itself? Second, let p(x) be a polynomial function (such as det) on V into F. What can we say about T if Tpreserves p(x), i.e. p(T(X)) = p(X) for all X in V?     

Differential inequalities for algebraic polynomials

We sharpen and supplement the results by V. I. Smirnov, A. Aziz, and Q. M. Dawood for algebraic polynomials which generalize the classical Bernstein and Erdos-Lax inequalities.     

Existence and uniqueness for Legendre curves

We give a moving frame of a Legendre curve (or, a frontal) in the unit tangent bundle and define a pair of smooth functions of a Legendre curve like as the curvature of a regular plane curve. It is quite useful to analyse the Legendre curves. The existence and uniqueness for Legendre curves hold similarly to the case of regular plane curves. As an application, we consider contact between Legendre curves and the arc-length parameter of Legendre immersions in the unit tangent bundle.     

Integral inequalities for algebraic and trigonometric polynomials

Doklady Mathematics - In this paper, we consider sharp estimates of integral functionals $int_0^{2pi } {phi (L|Lf_n (t)|)dt} $ for functions φ defined on the semiaxis (0, ∞) and...     

An algebraic structure for Faber polynomials

Let Σ be the set of functions, convergent for all |z|>1, with a Laurent series of the form f(z)=z+∑_n?0a_nz^-n. In this paper, we prove that the set of Faber polynomial sequences over Σ and the set of their normalized kth derivative sequences form groups which are isomorphic to the hitting time subgroup and the Bell^(k) subgroup of the Riordan group, respectively. Further, a relationship between such Faber polynomial sequences and Lucas and Sheffer polynomial sequences is derived.     

Connection between sets of uniqueness for multiplicative systems of functions and sets of uniqueness for multiplicative transforms

A problem of uniqueness for series over multiplicative systems of functions and for multiplicative transforms is considered. It is shown that each set of uniqueness for a multiplicative transform is specified by a countable collection of sets of uniqueness for series over the corresponding multiplicative system of functions. Each set of uniqueness for a series over a multiplicative system of functions is a portion on [0, 1) of some set of uniqueness for the corresponding multiplicative transform.     

On random algebraic polynomials

This paper provides asymptotic estimates for the expected number of real zeros and -level crossings of a random algebraic polynomial of the form , where are independent standard normal random variables and is a constant independent of . It is shown that these asymptotic estimates are much greater than those for algebraic polynomials of the form .

     

Clifford's inequality for real algebraic curves

We improve Clifford's Inequality for real algebraic curves. As an application we improve Harnack's Inequality for real space curves having a certain number of pseudo-lines. Another application involves the number of ovals that a real space curve can have.     

Sweeping algebraic curves for singular solutions

Many problems give rise to polynomial systems. These systems often have several parameters and we are interested to study how the solutions vary when we change the values for the parameters. Using predictor-corrector methods we track the solution paths. A point along a solution path is critical when the Jacobian matrix is rank deficient. The simplest case of quadratic turning points is well understood, but these methods no longer work for general types of singularities. In order not to miss any singular solutions along a path we propose to monitor the determinant of the Jacobian matrix. We examine the operation range of deflation and relate the effectiveness of deflation to the winding number. Computational experiments on systems coming from different application fields are presented.     

Inequalities of Rafalson type for algebraic polynomials

For a positive Borel measure dμ, we prove that the constantcan be represented by the zeros of orthogonal polynomials corresponding to dμ in case (i) dν(x)=(A+Bx)dμ(x), where A+Bx is nonnegative on the support of dμ and (ii) dν(x)=(A+Bx²)dμ(x), where dμ is symmetric and A+Bx² is nonnegative on the support of dμ. The extremal polynomials attaining the constant are obtained and some concrete examples are given including Markov-type inequality when dμ is a measure for Jacobi polynomials.     

Improvement of one inequality for algebraic polynomials

We prove that the inequality ||g (·/ n ) ||_L1[-1,1] ||P_n+k||_L1[-1,1] ￡ 2 ||gP_n+k||_L1[-1,1]\vert\vert g (\cdot / n ) \vert\vert_{L_{1}[-1,1]} \vert\vert P_{n+k}\vert\vert_{L_{1}[-1,1]} \leq 2 \vert\vert gP_{n+k}\vert\vert_{L_{1}[-1,1]}, where g : [-1, 1]→ℝ is a monotone odd function and P _n+k is an algebraic polynomial of degree not higher than n + k, is true for all natural n for k = 0 and all natural n ≥ 2 for k = 1. We also propose some other new pairs (n, k) for which this inequality holds. Some conditions on the polynomial P _n+k under which this inequality turns into the equality are established. Some generalizations of this inequality are proposed.     

An extremal problem for real algebraic polynomials

Let G _n be the set of all real algebraic polynomials of degree at most n, positive on the interval (?1, 1) and without zeros inside the unit circle (|z| < 1). In this paper an inequality for the polynomials from the set G _n is obtained. In one special case this inequality is reduced to the inequality given by B. Sendov [5] and in another special case it is reduced to an inequality between uniform norm and norm in the L ₂ space for the Jacobi weight.