this paper to ll this gap. To state our theorem we use the notation lim n=N!t X n;N = X 4 Kuijlaars and Van Assche to denote the property that in the doubly indexed sequence X n;N we have lim j!1 X n j ;N j = X whenever n j and N j are two sequences of natural numbers such that N j ! 1 and n j =N j ! t as j !1. For example, the convergence in Proposition 1.3 may be expressed by lim n=N!t (p n;N ) = w;t : We will use this notation throughout the rest of the paper. Our main result is the following. Theorem 1.4 Let for each N 2 N, two sequences fa n;N g 1 n=1 , a n;N > 0 and fb n;N g 1 n=0 of recurrence coecients be given, together with orthogonal polynomials p n;N generated by the recurrence xp n;N (x) = a n+1;N p n+1;N (x) + b n;N p n;N (x) + a n;N p n 1;N (x); n 0; (1.6) and the initial conditions p 0;N 1 and p 1;N 0. Suppose that there exist two continuous functions a : (0; 1) ! [0; 1), b : (0; 1) ! R, such that lim n=N!t a n;N = a(t); lim n=N!t b n;N = b(t) (1.7) whenever t > 0. Dene the functions (t) := b(t) 2a(t); (t) := b(t) + 2a(t); t > 0: (1.8) Then we have for every t > 0, lim n=N!t (p n;N ) = 1 t Z t 0 ! [(s);(s)] ds: (1.9) Here ! [;] is the measure given by (1.4) if < . If = , then ! [;] is the Dirac point mass at . Remark 1.5 The measure on the right-hand side of (1.9) is the average of the equilibrium measures of the varying intervals [(s); (s)] for 0 < s < t. Its support is given by " inf 0<s<t (s); sup 0<s<t (s) # : (1.10) In particular, the support is always an interval. The support is unbounded if or are unbounded near 0. J. Approx. Theory 99 (1999), 167-197. 5 Remark 1.6 Theorem 1.4 has an obvious extension to polynomials that are orthogonal with respect to a discrete measure supp...

The theory of the incomplete gamma functions, as part of the theory of conuent hypergeometric functions, has received its rst systematic exposition by Tricomi in the early 1950s. His own contributions, as well as further advances made thereafter, are surveyed here with particular emphasis on asymptotic expansions, zeros, inequalities, computational methods, and applications.

The paper discusses asymptotic methods for integrals, in particular uniform approximations. We discuss several examples, where we apply the results to Tricomi's \Psi\Gammafunction, in particular we consider an expansion of Tricomi-Carlitz polynomials in terms of Hermite polynomials. We mention other recent expansions for orthogonal polynomials that do not satisfy a differential equation, and for which methods based on integral representations produce powerful uniform asymptotic expansions. 1991 Mathematics Subject Classification: 41A60, 33B20, 33C10, 33C45, 11B73, 30E15. Keywords and Phrases: uniform asymptotic expansions, Tricomi's \Psi\Gammafunction, Kummer functions, confluent hypergeometric functions, Whittaker functions, Hermite polynomials, Tricomi-Carlitz polynomials. Note: Work carried out under project MAS2.8 Exploratory research. Extended version of a paper presented at the Conference Tricomi's Ideas and Contemporary Applied Mathematics to celebrate the 100th anniversary o...

. --- In a note at the end of his paper Recherches sur les fractions continues, Stieltjes gave a necessary and sufficient condition when a continued fraction is represented by a meromorphic function. This result is related to the study of compact Jacobi matrices. We indicate how this notion was developped and used since Stieltjes, with special attention to the results by M. G. Krein. We also pay attention to the perturbation of a constant Jacobi matrix by a compact Jacobi matrix, work which basically started with Blumenthal in 1889 and which now is known as the theory for the class M (a; b). Mots-cles : Op'erateurs de Jacobi compacts, polynomes orthogonaux, perturbations compacts, th'eorie spectral Key-words: Compact Jacobi matrices, orthogonal polynomials, compact pertubations, spectral theory AMS Classification: 42C05 40A15 47A10 --- --- --- --- 1. A theorem of Stieltjes Stieltjes' research in Recherches sur les fractions continues [25] deals with continued fractions of the form...

with varying recurrence coefficients