English

On sums of powers of zeros of polynomials

Classical Analysis and ODEs 2016-09-07 v1

Abstract

Due to Girard's (sometimes called Waring's) formula the sum of the rr-th power of the zeros of every one variable polynomial of degree NN, PN(x)P_{N}(x), can be given explicitly in terms of the coefficients of the monic P~N(x){\tilde P}_{N}(x) polynomial. This formula is closely related to a known \par \noindent N1N-1 variable generalization of Chebyshev's polynomials of the first kind, Tr(N1)T_{r}^{(N-1)}. The generating function of these power sums (or moments) is known to involve the logarithmic derivative of the considered polynomial. This entails a simple formula for the Stieltjes transform of the distribution of zeros. Perron-Stieltjes inversion can be used to find this distribution, {\it e.g.} for NN\to \infty.\par Classical orthogonal polynomials are taken as examples. The results for ordinary Chebyshev TN(x)T_{N}(x) and UN(x)U_{N}(x) polynomials are presented in detail. This will correct a statement about power sums of zeros of Chebyshev's TT-polynomials found in the literature. For the various cases (Jacobi, Laguerre, Hermite) these moment generating functions provide solutions to certain Riccati equations.

Keywords

Cite

@article{arxiv.math/9711217,
  title  = {On sums of powers of zeros of polynomials},
  author = {Wolfdieter Lang},
  journal= {arXiv preprint arXiv:math/9711217},
  year   = {2016}
}