Hostname: page-component-cd9895bd7-hc48f Total loading time: 0 Render date: 2024-12-23T12:00:51.840Z Has data issue: false hasContentIssue false

Solution of a generalized Schroeder equation in two variables

Published online by Cambridge University Press:  09 April 2009

C. F. Schubert
Affiliation:
University of California, Los Angeles.
Rights & Permissions [Opens in a new window]

Extract

Core share and HTML view are not available for this content. However, as you have access to this content, a full PDF is available via the ‘Save PDF’ action button.

If f(z) is analytic at the origin, f(0)=0, and f′(0)=λ, where 0< λ <1, then Koenigs' [3] solution of Schroeder's equation w(f(z))=λw(z), with multiplier λ, is given by . Here fn(z) denotes the nth iterate of f(z), defined inductively as f0(z)=z, f(fn-1(z)), n=1, 2, 3, …. More generally the solution w(z) of Schroeder's equation is uniquely determined to within a multiplicative constant by the requirement that it be analytic at the origin. From the uniqueness it follows that if g(z) is analytic at the origin, vanishes there, and commutes with f(z), i.e., f(g(z)) = g(f(z)), then w(g(z)) = w(z), for some multiplier a. Since w′(0) = 1 for Koenig's' solution, it has an inverse locally, and we find that g(z) is uniquely determined by its linear part; in fact g(z) = w-1w(z)). In particular the integral iterates of f can be put in the form w-1w(z)) for integral n. Thus for any α, real or complex, we may define fα(z), consistent with the above definition when α is a positive integer, as w-1w(z)). In this manner any function g(z) of the above type can be considered as an iterate of /(z). Also if cc, j9, 0 are any two distinct points sufficiently close to the origin there exists an analytic function g(z) which commutes with f(z) such that g(0) = 0, g(α) = β. In fact g(z)=w-1w(z)), where the multiplier χ=w(β)(w(α))-1. These facts are all well known, e.g. [2] [5], and we shall establish analogous results in a more general situation.

Type
Research Article
Copyright
Copyright © Australian Mathematical Society 1964

References

[1]Bellman, R., The iteration of power series in two variables, Duke Math. J. 19 (1952), 339347.CrossRefGoogle Scholar
[2]Hadamard, J., Two works on iteration and related questions, Bull. Amer. Math. Soc. 50 (1944), 6775.CrossRefGoogle Scholar
[3]Koenigs, G., Recherches sur les intégrales des certaines équations fonctionnelles, Ann. Sci. Ecole Norm. Sup. 3, supp. (1884), 341.CrossRefGoogle Scholar
[4]Leau, L., Sur les équations fonctionnelles à une ou à plusieurs variables, Ann. Fac. Sci. Toulouse, 11 (1897), E 1110.CrossRefGoogle Scholar
[5]Lémeray, M., Sur le problème de l'itération, C. R. Acad. Sci. Paris 128, (1899), 278.Google Scholar
[6]Montel, P., Leçons sur les recurrences et leurs applications, Gauthier-Villars, Paris, 1957.Google Scholar
[7]Sarsanov, A. A., Analytic iteration of functions of two variables. Soviet Math. 3 (1962), 452455.Google Scholar
[8]Szekeres, G., Regular iteration of real and complex functions, Acta Math. 100 (1958), 203258.CrossRefGoogle Scholar