An improvement on Nourein's method for the simultaneous determination of the zeroes of a polynomial (An algorithm)

In a recent paper [2], Nourein derived an iteration formula, which exhibited cubic convergence for the simultaneous determination of the zeroes of a polynomial. In this paper - following quite a different appraoch - we derive a method which can be viewed as an improvement on that of [2]. The derivation is based on the approximation of the polynomial in question by a Lagrange interpolation formula. We give the algorithm in ALGOL 60. For a given real polynomial, the algorithm caters for the general case of complex zeroes.     

On the Multiplicity of Zeroes of Polynomials with Quaternionic Coefficients

Regular polynomials with quaternionic coefficients admit only isolated zeroes and spherical zeroes. In this paper we prove a factorization theorem for such polynomials. Specifically, we show that every regular polynomial can be written as a product of degree one binomials and special second degree polynomials with real coefficients. The degree one binomials are determined (but not uniquely) by the knowledge of the isolated zeroes of the original polynomial, while the second degree factors are uniquely determined by the spherical zeroes. We also show that the number of zeroes of a polynomial, counted with their multiplicity as defined in this paper, equals the degree of the polynomial. While some of these results are known in the general setting of an arbitrary division ring, our proofs are based on the theory of regular functions of a quaternionic variable, and as such they are elementary in nature and offer explicit constructions in the quaternionic setting. Partially supported by G.N.S.A.G.A.of the I.N.D.A.M. and by M.I.U.R.. Lecture held by G. Gentili in the Seminario Matematico e Fisico on February 12, 2007. Received: August 2008     

On the Structure of the Set of Zeros of Quaternionic Polynomials

We prove that any quaternionic polynomial (with the coefficients on the same side) has two types of zeroes: the zeroes are either isolated or spherical ones, i.e., those ones which form a whole sphere. What is more, the total quantity of the isolated zeroes and of the double number of the spheres does not outnumber the degree of the polynomial.     

Note sur la méthode Bernoulli

Summary This note gives a solution to a problem of Henrici: Suppose a polynomial has exactly three dominant zeroes, one real, two complex conjugate. Devise a modification of Bernouilli's method that deals with this situation.     

Finding all real roots of a polynomial by matrix algebra and the Adomian decomposition method

In this paper, we put forth a combined method for calculation of all real zeroes of a polynomial equation through the Adomian decomposition method equipped with a number of developed theorems from matrix algebra. These auxiliary theorems are associated with eigenvalues of matrices and enable convergence of the Adomian decomposition method toward different real roots of the target polynomial equation. To further improve the computational speed of our technique, a nonlinear convergence accelerator known as the Shanks transform has optionally been employed. For the sake of illustration, a number of numerical examples are given.     

A generalization of Descartes’ rule of signs and fundamental theorem of algebra

Descartes’ rule of signs yields an upper bound for the number of positive and negative real roots of a given polynomial. The fundamental theorem of algebra implies a similar property; every real polynomial of degree n ? 1 has at most n real zeroes. In this paper, we describe axiomatically function families possessing one or another of these properties. The resulting families include, at least, all polynomial functions and sums of exponential functions. As an application of our approach, we consider, among other things, a method for identifying certain type of bases for the Euclidean space.     

Non-real zeroes of real entire derivatives

A real entire function belongs to the Laguerre-Pólya class LP if it is the limit of a sequence of real polynomials with real zeroes. By building upon results that resolved a long-standing conjecture of Wiman, a number of conditions are established under which a real entire function f must belong to the class LP, or to one of the related classes U _2p ^*. These conditions typically involve the non-real zeroes of f and its derivatives, or those of the differential polynomial f f″−a(f′)².     

On the number of real critical points of logarithmic derivatives and the Hawaii conjecture

For a given real entire function φ in the class U _2n ^*, n ≥ 0, with finitely many nonreal zeroes, we establish a connection between the number of real zeroes of the functions Q[φ] = (φ′/φ)′ and Q ₁[φ] = (φ″/φ′)′. This connection leads to a proof of the Hawaii Conjecture (T. Craven, G. Csordas, and W. Smith [5]), which states that if φ is a real polynomial, then the number of real zeroes of Q[φ] does not exceed the number of nonreal zeroes of φ.     

Optimal comparison of the <Emphasis Type="Italic">p</Emphasis>-norms of Dirichlet polynomials

In this sequel to Part I of this series [8], we present a different approach to bounding the expected number of real zeroes of random polynomials with real independent identically distributed coefficients or more generally, exchangeable coefficients. We show that the mean number of real zeroes does not grow faster than the logarithm of the degree. The main ingredients of our approach are Descartes’ rule of signs and a new anti-concentration inequality for the symmetric group. This paper can be read independently of part I in this series.     

Reelle algebraische Funktionen mit vorgegebenen Null- und Polstellen

This note continues the investigations of Knebusch on algebraic curves over real closed fields and was initiated by reading [3]. Especially we ask for the existence of real algebraic functions with given zeroes and poles, a question going back to Witt [4]. We study the real nature of coverings of real algebraic curves, and if the covering has degree two, we get algebraic proofs for results, which in the classical case have been obtained by topological methods in [2].     

Zeroes of Gaussian analytic functions with translation-invariant distribution

We study zeroes of Gaussian analytic functions in a strip in the complex plane, with translation-invariant distribution. We prove that the horizontal limiting measure of the zeroes exists almost surely, and that it is non-random if and only if the spectral measure is continuous (or degenerate). In this case, the limiting measure is computed in terms of the spectral measure. We compare the behavior with Gaussian analytic functions with symmetry around the real axis. These results extend a work by Norbert Wiener.     

The centroid of the zeroes of a polynomial via certain Laguerre-type operators

In this paper, we present several properties of the centroid of the zeroes of a polynomial. As an illustration, we apply these results to the d-orthogonal polynomials. Finally, we provide the relationship between different centroids of a general monic polynomial and its image under a certain Laguerre–type operator.     

Oscillation of analytic curves

The number of zeroes of the restriction of a given polynomial to the trajectory of a polynomial vector field in , in a neighborhood of the origin, is bounded in terms of the degrees of the polynomials involved. In fact, we bound the number of zeroes, in a neighborhood of the origin, of the restriction to the given analytic curve in of an analytic function, linearly depending on parameters, through the stabilization time of the sequence of zero subspaces of Taylor coefficients of the composed series (which are linear forms in the parameters). Then a recent result of Gabrielov on multiplicities of the restrictions of polynomials to the trajectories of polynomial vector fields is used to bound the above stabilization moment.

     

Polynomials with and without determinantal representations

The problem of writing real zero polynomials as determinants of linear matrix polynomials has recently attracted a lot of attention. Helton and Vinnikov [9] have proved that any real zero polynomial in two variables has a determinantal representation. Brändén [2] has shown that the result does not extend to arbitrary numbers of variables, disproving the generalized Lax conjecture. We prove that in fact almost no real zero polynomial admits a determinantal representation; there are dimensional differences between the two sets. The result follows from a general upper bound on the size of linear matrix polynomials. We then provide a large class of surprisingly simple explicit real zero polynomials that do not have a determinantal representation. We finally characterize polynomials of which some power has a determinantal representation, in terms of an algebra with involution having a finite dimensional representation. We use the characterization to prove that any quadratic real zero polynomial has a determinantal representation, after taking a high enough power. Taking powers is thereby really necessary in general. The representations emerge explicitly, and we characterize them up to unitary equivalence.     

Continuous optimization problems and a polynomial hierarchy of real functions

The close connection between the maximization operation and nondeterministic computation has been observed in many different forms. We examine this relationship on real functions and give a characterization of NP-time computable real functions by the maximization operation. A natural extension of NP-time computable real functions to a polynomial hierarchy of real functions has a characterization by alternating operations of maximization and minimization. Although syntactically this hierarchy of real functions can be treated as a polynomial hierarchy of operators, the well-known Baker-Gill-Solovay separation result does not apply to this hierarchy. This phenomenon is explained by the inherent structural properties of real functions, and is compared with recent studies on positive relativization.     

Some observations on the arithmetic of Eisenstein series for the modular group SL(2, \Bbb Z)

For even integers k\geqq4k\geqq4, let j_k(X)\varphi_k(X) be the separable rational polynomial that encodes the j-invariants of non-elliptic zeroes of the Eisenstein series E_k for the modular group SL(2,Bbb Z)(2,{Bbb Z}). We prove Kummer-type congruence properties for the j_k\varphi_k and, based on extensive calculations, make observations about the Galois group, the discriminant, and the distribution of zeroes of j_k(X)\varphi_k(X).     

Extrema of a Real Polynomial

In this paper, we investigate critical point and extrema structure of a multivariate real polynomial. We classify critical surfaces of a real polynomial f into three classes: repeated, intersected and primal critical surfaces. These different critical surfaces are defined by some essential factors of f, where an essential factor of f means a polynomial factor of f–c ₀, for some constant c ₀. We show that the degree sum of repeated critical surfaces is at most d–1, where d is the degree of f. When a real polynomial f has only two variables, we give the minimum upper bound for the number of other isolated critical points even when there are nondegenerate critical curves, and the minimum upper bound of isolated local extrema even when there are saddle curves. We show that a normal polynomial has no odd degree essential factors, and all of its even degree essential factors are normal polynomials, up to a sign change. We show that if a normal quartic polynomial f has a normal quadratic essential factor, a global minimum of f can be either easily found, or located within the interior(s) of one or two ellipsoids. We also show that a normal quartic polynomial can have at most one local maximum.     

On the distribution of zeroes of Artin–Schreier L-functions

We study the distribution of the zeroes of the L-functions of curves in the Artin–Schreier family. We consider the number of zeroes in short intervals and obtain partial results which agree with a random unitary matrix model.     

On Isolation of Real and Nearly Real Zeros of a Univariate Polynomial and Its Splitting into Factors

We show two simple algorithms for isolation of the real and nearly real zeros of a univariate polynomial, as well as of those zeros that lie on or near a fixed circle on the complex plane. We also simplify slightly approximation of complex zeros of a polynomial with real coefficients.     

Real class sizes

Following Wiener, we consider the zeroes of Gaussian analytic functions in a strip in the complex plane, with translation-invariant distribution. We show that the variance of the number of zeroes in a long horizontal rectangle [?T,T] × [a, b] is asymptotically between cT and CT², with positive constants c and C. We also supply with conditions (in terms of the spectral measure) under which the variance grows asymptotically linearly with T, as a quadratic function of T, or has intermediate growth. The results are compared with known results for real stationary Gaussian processes and other models.