An iterative approach toward hypergeometric accelerations

TL;DR

This paper develops an iterative acceleration method inspired by Chu and Ramanujan to derive and prove numerous hypergeometric series formulas for constants like 1/π, extending previous techniques with new iterative patterns.

Contribution

It introduces an iterative approach to hypergeometric acceleration methods, expanding on Wilf's technique and enabling the derivation of many Ramanujan-type formulas.

Findings

Derived numerous accelerated formulas for mathematical constants.

Extended Wilf's acceleration method using iterative patterns.

Connected new formulas to classical hypergeometric identities.

Abstract

Each of Ramanujan's series for $\frac{1}{\pi}$ is of the form $$ \sum_{n=0}^{\infty} z^n \frac{ (a_{1})_{n} (a_{2})_{n} (a_{3})_{n} }{ (b_{1})_{n} (b_{2})_{n} (b_{3})_{n} } (c_{1} n + c_2) $$ for rational parameters such that the difference between the arguments of any lower and upper Pochhammer symbols is not an integer. In accordance with the work of Chu, if an infinite sum of this form admits a closed form, then this provides a formula of Ramanujan type. Chu has introduced remarkable results on formulas of Ramanujan type, through the use of accelerations based on $\Omega$-sums related to classical hypergeometric identities. Building on our past work on an acceleration method due to Wilf relying on inhomogeneous difference equations derived from Zeilberger's algorithm, we extend this method through what we refer to as an iterative approach that is inspired by Chu's accelerations derived using iteration patterns for well-poised $\Omega$-sums and that we apply to introduce and prove many accelerated formulas of Ramanujan type for universal constants, along with many further accelerations related to the discoveries of Ramanujan, Guillera, and Chu.