On root arrangements for hyperbolic polynomial-like functions and their derivatives

A real polynomial P of degree n in one real variable is hyperbolic if its roots are all real. A real-valued function P is called a hyperbolic polynomial-like function (HPLF) of degree n if it has n real zeros and P(n) vanishes nowhere. Denote by the roots of P(i), k=1,…,n−i, i=0,…,n−1. Then in the absence of any equality of the form one has ∀i<j, (the Rolle theorem). For n?4 (resp. for n?5) not all arrangements without equalities (∗) of n(n+1)/2 real numbers and compatible with (∗∗) (we call them admissible) are realizable by the roots of hyperbolic polynomials (resp. of HPLFs) of degree n and of their derivatives. For n=5 we show that from 286 admissible arrangements, exactly 236 are realizable by HPLFs; from these 236 arrangements, 116 are realizable by hyperbolic polynomials and 24 by perturbations of such.     

Inclusion of the roots of a polynomial based on Gerschgorin's theorem

Summary In this note a new companion matrix is presented which can be interpreted as a product of Werner's companion matrices [13]. Gerschgorin's theorem yields an inclusion of the roots of a polynomial which is best in the sense of [4] and generalizes a result of L. Elsner [5]. This inclusion is better than the one due to W. Börsch-Supan in [1].Dedicated to Professor E. Stein on the occasion of his 60th birthday.     

On roots of polynomials with positive coefficients

We prove that an algebraic number α is a root of a polynomial with positive rational coefficients if and only if none of its conjugates is a nonnegative real number. This settles a recent conjecture of Kuba.     

Simple algorithms for approximating all roots of a polynomial with real roots

We present a simple algorithm for approximating all roots of a polynomial p(x) when it has only real roots. The algorithm is based on some interesting properties of the polynomials appearing in the Extended Euclidean Scheme for p(x) and p′(x). For example, it turns out that these polynomials are orthogonal; as a consequence, we are able to limit the precision required by our algorithm in intermediate steps. A parallel implementation of this algorithm yields a P-uniform NC₂ circuit, and the bit complexity of its sequential implementation is within a polylog factor of the bit complexity of the best known algorithm for the problem.     

On the fundamental theorem of algebra for polynomial equations over real composition algebras

A topological proof is given that real compositions algebras of finite dimension greater than one are algebraically closed under polynomial equations with a tame tail.     

On hermitian polynomial optimization

We compare three levels of algebraic certificates for evaluating the maximum modulus of a complex analytic polynomial, on a compact semi-algebraic set. They are obtained as translations of some recently discovered inequalities in operator theory. Although they can be stated in purely algebraic terms, the only known proofs for these decompositions have a transcendental character. Received: 27 June 2005     

On the minimum real roots of the adjoint polynomial of a graph

For a graph G, we denote by h(G,x) the adjoint polynomial of G. Let β(G) denote the minimum real root of h(G,x). In this paper, we characterize all the connected graphs G with .     

On approximation of a function and its derivatives by a polynomial and its derivatives

Let g∈C~q[-1, 1] be such that g~((k))(±1)=0 for k=0,…,q. Let P_n be an algebraic polynomialof degree at most n, such that P_n~((k))(±1)=0 for k=0,…,[_2~ (q+1)]. Then P_n and its derivativesP_n~((k)) for k≤q well approximate g and its respective derivatives, provided only that P_n well approxi-mates g itself in the weighted norm ‖g(x)-P_n(x) (1-x~2)~(1/2)~q‖This result is easily extended to an arbitrary f∈C~q[-1, 1], by subtracting from f the polynomial ofminnimal degree which interpolates f~((0))…,f~((q)) at±1. As well as providing easy criteria for judging the simultaneous approximation properties of a givenPolynomial to a given function, our results further explain the similarities and differences betweenalgebraic polynomial approximation in C~q[-1, 1] and trigonometric polynomial approximation in thespace of q times differentiable 2π-periodic functions. Our proofs are elementary and basic in character,permitting the construction of actual error estimates for simultaneous approximation proedures for smallvalues of q.     

On polynomial-like functions

A polynomial-like function (PLF) of degree n is a smooth function F whose nth derivative never vanishes. A PLF has ?n real zeros; in case of equality it is called hyperbolic; F(i) has ?n−i real zeros. We consider the arrangements of the n(n+1)/2 distinct real numbers , i=0,…,n−1, k=1,…,n−i, which satisfy the conditions . We ask the question whether all such arrangements are realizable by the roots of a hyperbolic PLF and its derivatives. We show that for n?5 the answer is negative.     

The computation of multiple roots of a polynomial

This paper considers structured matrix methods for the calculation of the theoretically exact roots of a polynomial whose coefficients are corrupted by noise, and whose exact form contains multiple roots. The addition of noise to the exact coefficients causes the multiple roots of the exact form of the polynomial to break up into simple roots, but the algorithms presented in this paper preserve the multiplicities of the roots. In particular, even though the given polynomial is corrupted by noise, and all computations are performed on these inexact coefficients, the algorithms ‘sew’ together the simple roots that originate from the same multiple root, thereby preserving the multiplicities of the roots of the theoretically exact form of the polynomial. The algorithms described in this paper do not require that the noise level imposed on the coefficients be known, and all parameters are calculated from the given inexact coefficients. Examples that demonstrate the theory are presented.     

On the zeros of a polynomial and its derivatives

If is univariate polynomial with complex coefficients having all its zeros inside the closed unit disk, then the Gauss-Lucas theorem states that all zeros of lie in the same disk. We study the following question: what is the maximum distance from the arithmetic mean of all zeros of to a nearest zero of ? We obtain bounds for this distance depending on degree. We also show that this distance is equal to for polynomials of degree 3 and polynomials with real zeros.

     

A Grobman-Hartman theorem for nonuniformly hyperbolic dynamics

We establish a version of the Grobman-Hartman theorem in Banach spaces for nonuniformly hyperbolic dynamics. We also consider the case of sequences of maps, which corresponds to a nonautonomous dynamics with discrete time. More precisely, we consider sequences of Lipschitz maps Am+fm such that the linear parts Am admit a nonuniform exponential dichotomy, and we establish the existence of a unique sequence of topological conjugacies between the maps Am+fm and Am. Furthermore, we show that the conjugacies are Hölder continuous, with Hölder exponent determined by the ratios of Lyapunov exponents with the same sign. To the best of our knowledge this statement appeared nowhere before in the published literature, even in the particular case of uniform exponential dichotomies, although some experts claim that it is well known in this case. We are also interested in the dependence of the conjugacies on the perturbations fm: we show that it is Hölder continuous, with the same Hölder exponent as the one for the conjugacies. We emphasize that the additional work required to consider the case of nonuniform exponential dichotomies is substantial. In particular, we need to consider several additional Lyapunov norms.     

Computing the real roots of a polynomial by the exclusion algorithm

We describe a new algorithm for localizing the real roots of a polynomialP(x). This algorithm determines intervals on whichP(x) does not possess any root. The remainder set contains the real roots ofP(x) and can be arbitrarily small.     

The Kalman-Yakubovich-Popov theorem for stabilizable hyperbolic boundary control systems

In this paper we present a version of the Kalman-Yakubovich-Popov theorem for a class of boundary control systems of hyperbolic type. Unstable, controllable systems are considered and stabilizability withunbounded feedbacks is permitted.Paper partially supported by the Italian MINISTERO DELLA RICERCA SCIENTIFICA E TECNOLOGICA within the program of GNAFA-CNR and by NATO CRG program SA.5-2-05 (CRG940161).     

On the Location of Pseudozeros of a Complex Interval Polynomial

Given a univariate complex interval polynomial F, we provide a rigorous method for deciding whether there exists a pseudozero of F in a prescribed closed complex domain D. Here a pseudozero of F is defined to be a zero of some polynomial in F. We use circular intervals and assume that the boundary C of D is a simple curve and that C is the union of a finite number of arcs, each of which is represented by a rational function. When D is not bounded, we assume further that all the polynomials in F are of the same degree. Examples of such domains are the outside of an open disk and a half-plane with boundary. Our decision method uses the representation of C and the property that a polynomial in F is of degree 1 with respect to each coefficient regarded as a variable.      

Smooth center manifolds for nonuniformly partially hyperbolic trajectories

We establish the existence of unique smooth center manifolds for ordinary differential equations v^′=A(t)v+f(t,v) in Banach spaces, assuming that v^′=A(t)v admits a nonuniform exponential trichotomy. This allows us to show the existence of unique smooth center manifolds for the nonuniformly partially hyperbolic trajectories. In addition, we prove that the center manifolds are as regular as the vector field. Our proof of the Ck smoothness of the manifolds uses a single fixed point problem in an appropriate complete metric space. To the best of our knowledge we establish in this paper the first smooth center manifold theorem in the nonuniform setting.