ON SETS OF ZEROES OF CLIFFORD ALGEBRA-VALUED POLYNOMIALS

In this note, we study zeroes of Clifford algebra-valued polynomials. We prove that if such a polynomial has only real coefficients, then it has two types of zeroes： the real isolated zeroes and the spherical conjugate ones. The total number of zeroes does not exceed the degree of the polynomial. We also present a technique for computing the zeroes.     

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.     

Slice monogenic functions

In this paper we offer a new definition of monogenicity for functions defined on ℝ ⁿ⁺¹ with values in the Clifford algebra ℝ _n following an idea inspired by the recent papers [6], [7]. This new class of monogenic functions contains the polynomials (and, more in general, power series) with coefficients in the Clifford algebra ℝ _n . We will prove a Cauchy integral formula as well as some of its consequences. Finally, we deal with the zeroes of some polynomials and power series.     

Lowest Landau level functional and Bargmann spaces for Bose-Einstein condensates

A fast rotating Bose-Einstein condensate can be described by a complex valued wave function minimizing an energy restricted to the lowest Landau level or Fock-Bargmann space. Using some structures associated with this space, we study the distribution of zeroes of the minimizer and prove in particular that the number of zeroes is infinite. We relate their location to the combination of two problems: a confining problem producing an inverted parabola profile and the Abrikosov problem of minimizing an energy on a lattice, using Theta functions.     

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     

Zur Einbettung uniform bewerteter Ternärkörper in Hahn-Ternärkörper

In this paper, we generalize the results of [12] and derive criteria for the regular embeddability of a uniformly valued ternary field into an appropriate Hahn ternary field of formal power series with coefficients in the residue ternary field and exponents in the value loop. Furthermore, we discuss these criteria also for richer algebraic structures and we give an example for the skew field case.

     

Outliers in the spectrum of iid matrices with bounded rank perturbations

It is known that if one perturbs a large iid random matrix by a bounded rank error, then the majority of the eigenvalues will remain distributed according to the circular law. However, the bounded rank perturbation may also create one or more outlier eigenvalues. We show that if the perturbation is small, then the outlier eigenvalues are created next to the outlier eigenvalues of the bounded rank perturbation; but if the perturbation is large, then many more outliers can be created, and their law is governed by the zeroes of a random Laurent series with Gaussian coefficients. On the other hand, these outliers may be eliminated by enforcing a row sum condition on the final matrix.     

Entire functions of exponential type represented by pseudo-random and random Taylor series

We study the influence of the multipliers ξ(n) on the angular distribution of zeroes of the Taylor series \({F_\xi }\left( z \right) = \sum\limits_{n \geqslant 0} {\xi \left( n \right)} \frac{{{z^n}}}{{n!}}\).We show that the distribution of zeroes of Fξ is governed by certain autocorrelations of the sequence ξ. Using this guiding principle, we consider several examples of random and pseudo-random sequences ξ and, in particular, answer some questions posed by Chen and Littlewood in 1967.As a by-product, we show that if ξ is a stationary random integer-valued sequence, then either it is periodic, or its spectral measure has no gaps in its support. The same conclusion is true if ξ is a complex-valued stationary ergodic sequence that takes values in a uniformly discrete set.     

Domain decomposition preconditioners for multiscale problems in linear elasticity

We analyze two‐level overlapping Schwarz domain decomposition methods for vector‐valued piecewise linear finite element discretizations of the PDE system of linear elasticity. The focus of our study lies in the application to compressible, particle‐reinforced composites in 3D with large jumps in their material coefficients. We present coefficient‐explicit bounds for the condition number of the two‐level additive Schwarz preconditioned linear system. Thereby, we do not require that the coefficients are resolved by the coarse mesh. The bounds show a dependence of the condition number on the energy of the coarse basis functions, the coarse mesh, and the overlap parameters, as well as the coefficient variation. Similar estimates have been developed for scalar elliptic PDEs by Graham et al. 1 The coarse spaces to which they apply here are assumed to contain the rigid body modes and can be considered as generalizations of the space of piecewise linear vector‐valued functions on a coarse triangulation. The developed estimates provide a concept for the construction of coarse spaces, which can lead to preconditioners that are robust with respect to high contrasts in Young's modulus and the Poisson ratio of the underlying composite. To confirm the sharpness of the theoretical findings, we present numerical results in 3D using vector‐valued linear, multiscale finite element and energy‐minimizing coarse spaces. The theory is not restricted to the isotropic (Lamé) case, extends to the full‐tensor case, and allows applications to multiphase materials with anisotropic constituents in two and three spatial dimensions. However, the bounds will depend on the ratio of largest to smallest eigenvalue of the elasticity tensor.     

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.     

The nil radical of power series rings

We describe the nil radical of power series rings in non-commuting indeterminates by showing that a series belongs to the radical if and only if the ideal generated by its coefficients is nilpotent. We also show thatt the principal ideals generated by elements of the nil radical of the power series ring in one indeterminate are nil of bounded index.     

A note on rationality of orbital integrals on a P-adic group

We prove that if rational measures are used on p-adic reductive groups then the orbital integrals of any given smooth and compactly supported complex valued function belong to the field generated by the values of that function. We also show that the Shalika germs are then rational valued functions. As a consequence, we are able to show, in certain cases, that the coefficients appearing in the Harish-Chandra local character expansion are rational numbers. Research supported by NSERC     

Maps on Ultrametric Spaces,Hensel's Lemma,and Differential Equations Over Valued Fields

We give a criterion for maps on ultrametric spaces to be surjective and to preserve spherical completeness. We show how Hensel's Lemma and the multidimensional Hensel's Lemma follow from our result. We give an easy proof that the latter holds in every henselian field. We also prove a basic infinite-dimensional Implicit Function Theorem. Further, we apply the criterion to deduce various versions of Hensel's Lemma for polynomials in several additive operators, and to give a criterion for the existence of integration and solutions of certain differential equations on spherically complete valued differential fields, for both valued D-fields in the sense of Scanlon, and differentially valued fields in the sense of Rosenlicht. We modify the approach so that it also covers logarithmic-exponential power series fields. Finally, we give a criterion for a sum of spherically complete subgroups of a valued abelian group to be spherically complete. This in turn can be used to determine elementary properties of power series fields in positive characteristic.     

A “Sup + C Inf” inequality for Liouville‐type equations with singular potentials

We generalize a Harnack‐type inequality (I. Shafrir, C. R. Acad. Sci. Paris, 315 (1992), 159–164), for solutions of Liouville equations to the case where the weight function may admit zeroes or singularities of power‐type |x|^2α, with α ∈ (?1, 1). © 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim     

幂级数系数重排使型不变的必要条件

根据幂级数系数重排级不变的充要条件，对比研究了幂级数系数的重排与此级数的和函数的型之间的关系，得到了幂级数系数重排型不变的一些必要条件。     

Solutions for PDEs with constant coefficients and derivability of functions ranged in commutative algebras

Given a PDE with real or complex partial derivatives and with constant coefficients, we propose a method of assigning to it a set of algebra‐valued functions in such a manner that the components of the latter are solutions of the PDE. Copyright © 2013 John Wiley & Sons, Ltd.     

A functional calculus in hilbert space based on operator valued analytic functions

A homomorphic map is defined from the algebra of norm bounded analyticN-operator valued functions in the unit disc into the algebra of bounded operators in Hilbert spaces represented as left invariant subspaces ofH ²(N), and the spectral properties of the map are studied. The subclass of functions having norm bound one in the disc is characterized in terms of the power series coefficients. This paper was partially supported by the National Science Foundation under contract NSF GP-5455.     

Arithmetic Continuation of Regular Roots of Formal Parametric Polynomial Systems

Given a regular system of polynomial equations with power series coefficients, an initial root is continued as a power series. With the ground domain as an arbitrary field, arithmetic alone is used for the root continuation over this field, and computation is quadratic in the number of computed coefficients. If the power series of the coefficients of the polynomial are geometrically bounded, then the coefficients of the power series of the root are also.     

On a vector q‐d algorithm

Using the framework provided by Clifford algebras, we consider a non‐commutative quotient‐difference algorithm for obtaining the elements of a continued fraction corresponding to a given vector‐valued power series. We demonstrate that these elements are ratios of vectors, which may be calculated with the aid of a cross rule using only vector operations. For vector‐valued meromorphic functions we derive the asymptotic behaviour of these vectors, and hence of the continued fraction elements themselves. The behaviour of these elements is similar to that in the scalar case, while the vectors are linked with the residues of the given function. In the particular case of vector power series arising from matrix iteration the new algorithm amounts to a generalisation of the power method to sub‐dominant eigenvalues, and their eigenvectors. This revised version was published online in June 2006 with corrections to the Cover Date.