Abstract
We obtain upper and lower bounds for Christoffel functions for Freud weights by relatively new methods, including a new way to estimate discretization of potentials. We then deduce bounds for orthogonal polynomials onℝ thereby largely resolving a 1976 conjecture of P. Nevai. For example, let W:=e −Q, whereQ:ℝ→ℝ is even and continuous inℝ, Q" is continuous in (0, ∞) andQ '>0 in (0, ∞), while, for someA, B,
Leta n denote thenth Mhaskar-Rahmanov-Saff number forQ, andL>0. Then, uniformly forn≥1 and |x|≤a n (1+Ln −2/3),
Moreover, for all x εℝ, we can replace ∼ by ≥. In particular, these results apply toW(x):=exp(-|x|α), α>1. We also obtain lower bounds for allx εℝ, when onlyA>0, but this necessarily requires a more complicated formulation.
We deduce that thenth orthonormal plynomialp n (W 2, ·). forW 2 satisfies
and
In particular, this applies toW(x):=exp(-|x|α), α>1.
Similar content being viewed by others
References
W. C. Bauldry (1990):Estimates of asymmetric Freud polynomials on the real line. J. Approx. Theory,63:225–237.
S. S. Bonan (1983):Applications of G. Freud's theory I. In: Approximation Theory IV (C. K. Chui, L. L. Schumaker, J. D. Ward, eds.). New York: Academic Press, pp. 347–351.
S. S. Bonan, D. S. Clark (1990):Estimates of the Hermite and the Freud polynomials. J. Approx. Theory,63:210–224.
J. Clunie, T. Kövari (1968):On integral functions having prescribed asymptotic growth II. Canad. J. Math.,20:7–20.
G. Freud (1977):On estimations of the greatest zeros of orthogonal polynomials. Acta Math. Acad. Sci. Hungar.,25:99–107.
G. Freud (1977):On Markov-Bernstein type inequalities and their applications. J. Approx. Theory,19:22–37.
G. Freud, A. Giroux, Q. I. Rahman (1978):On approximation by polynomials with weight exp(-|x|). Canad. J. Math.,30:358–372 (in French).
T. Ganelius (1976):Rational approximation in the complex plane and on the line. Ann. Acad. Sci. Fenn.,2:129–145.
A. Knopfmacher, D. S. Lubinsky (1987):Mean convergence of Lagrange interpolation for Freud's weights with application to product integration rules. J. Comput. Appl. Math.,17:79–103.
A. L. Levin, D. S. Lubinsky (1987):Canonical products and the weights exp(-|x|α), α>1,with applications. J. Approx. Theory,49:149–169.
A. L. Levin, D. S. Lubinsky (1987):Weights on the real line that admit good relative polynomial approximation, with applications. J. Approx. Theory.,49:170–195.
A. L. Levin, D. S. Lubinsky (1990):L ∞ Markov and Bernstein inequalities for Freud weights. SIAM J. Math. Anal.,21:1065–1082.
D. S. Lubinsky (1986):Gaussian quadrature, weights on the whole real line, and even entive functions with non-negative even order derivatives. J. Approx. Theory,46:297–313.
D. S. Lubinsky (1989): Strong Asymptotics for Extremal Errors and Polynomials Associated with Erdös-Type Weights. Pitman Research Notes in Mathematics, vol. 202. Harlow, Essex: Longman.
D. S. Lubinsky, E. B. Saff (1988): Strong Asymptotics for Extremal polynomials Associated with Exponential Weights. Lecture Notes in Mathematics, vol. 1305. Berlin: Springer-Verlag.
A. Mate, P. Nevai, V. Totik (1986):Asymptotics for the zeros of orthogonal polynomials associated with infinite intervals. J. London Math. Soc.,33:303–310.
H. N. Mhaskar (1990):Bounds for certain Freud-type orthogonal polynomials. J. Approx. Theory,63:238–254.
H. N. Mhaskar, E. B. Saff (1984):Extremal Problems for Polynomials with Exponential Weights. Trans. Amer. Math. Soc.,285:203–234.
H. N. Mhaskar, E. B. Saff (1985):Where does the sup-norm of a weighted polynomial live? Constr. Approx.,1:71–91.
H. N. Mhaskar, E. B. Saff (1987):Where does the L p -norm of a weighted polynomial live? Trans. Amer. Math. Soc.,303:109–124.
P. Nevai (1976):Lagrange interpolation at the zeros of orthogonal polynomials. In: Approximation Theory II (G. G. Lorentz, C. K. Chui, and L. L. Schumaker, eds.). New York: Academic Press, pp. 163–201.
P. Nevai (1979): Orthogonal Polynomials. Memoirs of the American Mathematical Society, no. 213. Providence, RI: American Mathematical Society.
P. Nevai (1984):Asymptotics for orthogonal polynomials associated with exp(−x 4). SIAM J. Math. Anal.,15:1177–1187.
P. Nevai (1986):Geza Freud, orthogonal polynomials and Christoffel functions. A case study. J. Approx. Theory,48:3–167.
P. Nevai, V. Totik (1986):Weighted polynomial inequalities. Constr. Approx.,2:113–127.
D. J. Newman, A. R. Reddy (1977):Rational approximation to |x|/(1+x 2m)on (−∞, ∞). J. Approx. Theory,19:231–238.
E. A. Rahmanov (1984):On asymptotic properties of polynomials orthogonal on the real axis. Math. USSR-Sb.,47:155–193.
E. A. Rahmanov (1991):Strong asymptotics for orthogonal polynomials associated with exponential weights onℝ. Manuscript.
R. C. Sheen (1987):Plancherel-Rotach type asymptotics for orthogonal polynomials associated with exp(−x 6/6). J. Approx. Theory,50:232–293.
G. A. Szegö (1975). Orthogonal Polynomials, 4th edn. American Mathematical Society Colloquium Publications, vol. 23. Providence, RI: American Mathematical Society.
Author information
Authors and Affiliations
Additional information
Communicated by Vilmos Totik
Rights and permissions
About this article
Cite this article
Levin, A.L., Lubinsky, D.S. Christoffel functions, orthogonal polynomials, and Nevai's conjecture for Freud weights. Constr. Approx 8, 463–535 (1992). https://doi.org/10.1007/BF01203463
Received:
Revised:
Issue Date:
DOI: https://doi.org/10.1007/BF01203463