Hypergeometric analogues of the AGM iteration

Borwein, Jonathan M. and Borwein, Peter and Garvan, F.G. (1993) Hypergeometric analogues of the AGM iteration. Constructive Approximation, 9 . pp. 509-523.

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The arithmetic-geometric mean iteration of Gauss and Legendre is the two-term iteration an+1=(an+bn)/2 and bn+1 = [formula could not be replicated] with ao:=1 and bo:=x. The common limit is 2F1(½,½;1;1−x2)-1 and the convergence is quadratic. This is a rare object with very few close relatives. There are however three other hypergeometric functions for which we expect similar iterations to exist, namely:2F1(½−s1,½ + s; 1;·) with s=1/3, 1/4, 1/6. Our intention is to exhibit explicitly these iterations and some of their generalizations. These iterations exist because of underlying quadratic or cubic transformations of certain hypergeometric functions, and thus the problem may be approached via searching for invariances of the corresponding second-order differential equations. It may also be approached by searching for various quadratic and cubic modular equations for the modular forms that arise on inverting the ratios of the solutions of these differential equations. In either case, the problem is intrinsically computational. Indeed, the discovery of the identities and their proofs can be effected almost entirely computationally with the aid of a symbolic manipulation package, and we intend to emphasize this computational approach.

Item Type: Article
Depositing User: Mrs Naghmana Tehseen
Date Deposited: 14 Jan 2015 16:05
Last Modified: 14 Jan 2015 16:05

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