On polar Legendre polynomials

10 pages, no figures.-- MSC2000 codes: Primary 42C05; Secondary 33C25.-- ArXiv pre-print available at: http://arxiv.org/abs/0709.4537Accepted in Rocky Mountain Journal of Mathematics.We introduce a new class of polynomials {Pn}, that we call polar Legendre polynomials, they appear as solutions of an inverse Gauss problem of equilibrium position of a field of forces with n + 1 unit masses. We study algebraic, differential and asymptotic properties of this class of polynomials, that are simultaneously orthogonal with respect to a differential operator and a discrete-continuous Sobolev type inner product.Research by first author (H.P.) was partially supported by Dirección General de Investigación, Ministerio de Ciencia y Tecnología de España, under grant MTM2006-13000-C03-02, by Comunidad de Madrid-Universidad Carlos III de Madrid, under grant CCG06-UC3M/EST-0690 and by Centro de Investigación Matemática de Canarias (CIMAC). Research by second author (J.Y.B.) was supported by CNPq-TWAS. Research by third author (W.U.) was partially supported by Centro de Investigación Matemática de Canarias (CIMAC).En prens

Iterated integrals of Jacobi polynomials

Let P(α,β)n be the n-th monic Jacobi polynomial with α,β>−1. Given m numbers ω1,…,ωm∈C∖[−1,1], let Ωm=(ω1,…,ωm) and P(α,β)n,m,Ωm be the m-th iterated integral of (n+m)!n!P(α,β)n normalized by the conditions dkP(α,β)n,m,Ωmdzk(ωm−k)=0, for k=0,1,…,m−1. The main purpose of the paper is to study the algebraic and asymptotic properties of the sequence of monic polynomials {P(α,β)n,m,Ωm}n. In particular, we obtain the relative asymptotic for the ratio of the sequences {P(α,β)n,m,Ωm}n and {P(α,β)n}n. We prove that the zeros of these polynomials accumulate on a suitable ellipse.The research of H. Pijeira was supported by research Grant MTM2015-65888-C4-2-P Ministerio de Economía y Competitividad of Spain

Differential orthogonality: Laguerre and Hermite cases with applications

Let μ be a finite positive Borel measure supported on R , L[f]=xf′′+(α+1−x)f′ with α>−1 , or L[f]=12f′′−xf′ , and m a natural number. We study algebraic, analytic and asymptotic properties of the sequence of monic polynomials {Qn}n>m that satisfy the orthogonality relations ∫L[Qn](x)xkdμ(x)=0for all0≤k≤n−1. Turn MathJax off We also provide a fluid dynamics model for the zeros of these polynomials.The authors thank the comments and suggestions made by the referees which helped improve the manuscript. First author’s research was partially supported by FAPESP of Brazil, under grant 2012/21042-0. First and second authors’ research was partially supported by Ministerio de Economía y Competitividad of Spain, under grant MTM2012-36732-C03-01

Bases of the space of solutions of some fourth-order linear difference equations: applications in rational approximation

It is very well known that a sequence of polynomials {Q(n)(x)}(n=0)(infinity) orthogonal with respect to a Sobolev discrete inner product (s) = integral(I)fg d mu + lambda f(-1)(0)g'(0); lambda is an element of R+; where mu is a finite Borel measure and I is an interval of the real line, satisfies a five- term recurrence relation. In this contribution we study other three families of polynomials which are linearly independent solutions of such a five- term linear difference equation and, as a consequence, we obtain a polynomial basis of such a linear space. They constitute the analogue of the associated polynomials in the standard case. Their explicit expression in terms of {Q(n)(x)}(n=0)(infinity) using an integral representation is given. Finally, an application of these polynomials in rational approximation is shown

Hessenberg-Sobolev matrices and Favard type theorem

We study the relation between certain non-degenerate lower Hessenberg infinite matrices G and the existence of sequences of orthogonal polynomials with respect to Sobolev inner products. In other words, we extend the well-known Favard theorem for Sobolev orthogonality. We characterize the structure of the matrix G and the associated matrix of formal moments MG in terms of certain matrix operators.The research of I. Pérez-Yzquierdo was partially supported by Fondo Nacional de Innovación y Desarrollo Científico y Tecnológico (FONDOCYT), Dominican Republic, under grant 2016-2017-080 No. 013-2018. The authors thank the reviewers for theirs constructive comments and suggestions that helped to improve the clarity of this manuscript. Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature

Asymptotic zero distribution for a class of extremal polynomials

We consider extremal polynomials with respect to a Sobolev-type p-norm, with 1and measures supported on compact subsets of the real line. For a wide class of such extremal polynomials with respect to mutually singular measures (i.e. supported on disjoint subsets of the real line), it is proved that their critical points are simple and contained in the interior of the convex hull of the support of the measures involved and the asymptotic critical point distribution is studied. We also find the nth root asymptotic behavior of the corresponding sequence of Sobolev extremal polynomials and their derivatives.A.D.G. was supported by the Research Fellowship Program, Ministerio de Economía, Industria y Competitividad of Spain, under grant BES-2016-076613. The authors G.L.L. and H.P.C. were supported by the Ministerio de Economía, Industria y Competitividad of Spain, under grant MTM2015-65888-C4-2-P

Differential properties of Jacobi-Sobolev polynomials and electrostatic interpretation

This article belongs to the Special Issue Orthogonal Polynomials and Special Functions: Recent Trends and Their Applications.We study the sequence of monic polynomials {S-n}n >= 0, orthogonal with respect to the JacobiSobolev inner product s = integral(1)(-1) f (x)g(x) d mu(alpha,beta)(x) + Sigma (N)(dj)(j=1) lambda(j,k),f(k) (c(j))g((k))(cj), where N, d(j) is an element of Z(+), lambda(j,k) >= 0, d mu(alpha,beta)(x) = (1-x)(alpha)(1 + x)beta (dx), alpha, beta > -1, and c(j) is an element of R backslash(-1, 1). A connection formula that relates the Sobolev polynomials Sn with the Jacobi polynomials is provided, as well as the ladder differential operators for the sequence {S-n}(n >= 0) and a second-order differential equation with a polynomial coefficient that they satisfied. We give sufficient conditions under which the zeros of a wide class of Jacobi-Sobolev polynomials can be interpreted as the solution of an electrostatic equilibrium problem of n unit charges moving in the presence of a logarithmic potential. Several examples are presented to illustrate this interpretation.The research of J. Toribio-Milane was partially supported by Fondo Nacional de Innovación y Desarrollo Científico y Tecnológico (FONDOCYT), Dominican Republic, under grant 2020-2021-1D1-137.Publicad

Logarithmic asymptotics of contracted Sobolev extremal polynomials on the real line

12 pages, no figures.-- MSC2000 codes: 41A60, 46E35.MR#: MR2271726 (2007h:41031)Zbl#: Zbl 1106.41031For a wide class of Sobolev type norms with respect to measures with unbounded support on the real line, the contracted zero distribution and the logarithmic asymptotic of the corresponding re-scaled Sobolev orthogonal polynomials is given.G. López, F. Marcellán, and H. Pijeira were supported by Ministerio de Ciencia y Tecnología of Spain under Grant BFM 2003-06335-C03-02. G. López and F. Marcellán were also partially supported by INTAS Research Network NeCCA INTAS 03-51-6637 and NATO PST.CLG.979738.Publicad

Polynomials of least deviation from zero in Sobolev p-Norm

The first part of this paper complements previous results on characterization of polynomials of least deviation from zero in Sobolev p-norm (1<p<∞) for the case p=1. Some relevant examples are indicated. The second part deals with the location of zeros of polynomials of least deviation in discrete Sobolev p-norm. The asymptotic distribution of zeros is established on general conditions. Under some order restriction in the discrete part, we prove that the n-th polynomial of least deviation has at least n−d∗ zeros on the convex hull of the support of the measure, where d∗ denotes the number of terms in the discrete part.The research of H. Pijeira-Cabrera was partially supported by Ministry of Science, Innovation and Universities of Spain, under grant PGC2018-096504-B-C33. Funding Open Access funding provided by Universidad Carlos III de Madrid thanks to the CRUE-CSIC 2021 agreement with Springer Nature

Discrete-continuous Jacobi-Sobolev spaces and Fourier series

Let p≥1,ℓ∈N,α,β>−1 and ϖ=(ω0,ω1,…,ωℓ−1)∈Rℓ. Given a suitable function f, we define the discrete–continuous Jacobi–Sobolev norm of f as: ∥f∥s,p:=(∑k=0ℓ−1∣∣f(k)(ωk)∣∣p+∫1−1∣∣f(ℓ)(x)∣∣pdμα,β(x))1p, where dμα,β(x)=(1−x)α(1+x)βdx. Obviously, ∥⋅∥s,2=⟨⋅,⋅⟩s−−−−√, where ⟨⋅,⋅⟩s is the inner product ⟨f,g⟩s:=∑k=0ℓ−1f(k)(ωk)g(k)(ωk)+∫1−1f(ℓ)(x)g(ℓ)(x)dμα,β(x). In this paper, we summarize the main advances on the convergence of the Fourier–Sobolev series, in norms of type Lp, in the continuous and discrete cases, respectively. Additionally, we study the completeness of the Sobolev space of functions associated with the norm ∥⋅∥s,p and the denseness of the polynomials. Furthermore, we obtain the conditions for the convergence in ∥⋅∥s,p norm of the partial sum of the Fourier–Sobolev series of orthogonal polynomials with respect to ⟨⋅,⋅⟩s.Authors thank the valuable comments by the referees. Their suggestions have contributed to improve the presentation of this manuscript. The research of F. Marcellán and H. Pijeira-Cabrera was partially supported by Spanish State Research Agency, under Grant PGC2018-096504-B-C33. The research of A. Díaz-González was supported by the Research Fellowship Program, Ministry of Economy and Competitiveness of Spain, under grant BES-2016-076613