Lie-Butcher series, Geometry, Algebra and Computation

TL;DR

This paper reviews the algebraic structures of Lie-Butcher series, generalizing classical B-series to Lie groups and manifolds, and reformulates algebraic operations as recursive formulas to aid software development.

Contribution

It presents a concise, self-contained overview of the algebraic structures of LB-series and reformulates key operations as recursive formulas for computational implementation.

Findings

Algebraic structures of LB-series are clarified and summarized.

Recursive formulas for algebraic operations are developed.

Foundation laid for software library in Haskell for LB-series computations.

Abstract

Lie-Butcher (LB) series are formal power series expressed in terms of trees and forests. On the geometric side LB-series generalizes classical B-series from Euclidean spaces to Lie groups and homogeneous manifolds. On the algebraic side, B-series are based on pre-Lie algebras and the Butcher-Connes-Kreimer Hopf algebra. The LB-series are instead based on post-Lie algebras and their enveloping algebras. Over the last decade the algebraic theory of LB-series has matured. The purpose of this paper is twofold. First, we aim at presenting the algebraic structures underlying LB series in a concise and self contained manner. Secondly, we review a number of algebraic operations on LB-series found in the literature, and reformulate these as recursive formulae. This is part of an ongoing effort to create an extensive software library for computations in LB-series and B-series in the programming language Haskell.