Faà di Bruno's formula and inversion of power series

Samuel Johnston, Joscha Prochno

Research output: Contribution to journalArticlepeer-review

Abstract

Faà di Bruno's formula gives an expression for the derivatives of the composition of two real-valued functions. In this paper we prove a multivariate and synthesised version of Faà di Bruno's formula in higher dimensions, providing a combinatorial expression for the derivatives of chain compositions of functions in terms of sums over labelled trees. We give several applications of this formula, including a new involution formula for the inversion of multivariate power series. We use this framework to outline a combinatorial approach to studying the invertibility of polynomial mappings, giving a purely combinatorial restatement of the Jacobian conjecture. Our methods extend naturally to the non-commutative case, where we prove a free version of Faà di Bruno's formula for multivariate power series in free indeterminates, and use this formula as a tool for obtaining a new inversion formula for free power series.
Original languageEnglish
Article number108080
JournalAdvances in Mathematics
Volume395
Early online date19 Nov 2021
DOIs
Publication statusPublished - 24 Feb 2022

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