A relatively short self-contained proof of the Baker-Campbell-Hausdorff theorem

A simple and efficient algorithm for computing the Baker-Campbell-Hausdorff series

A new algorithm for computing coefficients of the Baker--Campbell--Hausdorff series is presented, which can be straightforwardly implemented in any general-purpose programming language or computer algebra system. The algorithm avoids rational arithmetic and performs all its calculations in pure integer arithmetic, allowing for a very efficient implementation. An implementation in the Julia programming language is available.

A Non-associative Baker-Campbell-Hausdorff formula

We address the problem of constructing the non-associative version of the Dynkin form of the Baker-Campbell-Hausdorff formula; that is, expressing $\log (\exp (x)\exp(y))$, where $x$ and $y$ are non-associative variables, in terms of the Shestakov-Umirbaev primitive operations. In particular, we obtain a recursive expression for the Magnus expansion of the Baker-Campbell-Hausdorff series and an explicit formula in degrees smaller than 5. Our main tool is a non-associative version of the Dynkin-Specht-Wever Lemma. A construction of Bernouilli numbers in terms of binary trees is also recovered.

Baker-Campbell-Hausdorff公式的Eichler证明的一个变体

A variation of Eichler's proof of the Baker-Campbell-Hausdorff formula

本文提出了Baker-Campbell-Hausdorff公式的Eichler证明的变体，通过四指数乘积结合性简化证明，得到初等简洁的短证明，还推出不含显式伯努利数的递推格式。

The Baker-Campbell-Hausdorff formula via mould calculus

The well-known Baker-Campbell-Hausdorff theorem in Lie theory says that the logarithm of a noncommutative product e X e Y can be expressed in terms of iterated commutators of X and Y. This paper provides a gentle introduction t{ó} Ecalle's mould calculus and shows how it allows for a short proof of the above result, together with the classical Dynkin explicit formula [Dy47] for the logarithm, as well as another formula recently obtained by T. Kimura [Ki17] for the product of exponentials itself. We also analyse the relation between the two formulas and indicate their mould calculus generalizat…

Denominators of coefficients of the Baker-Campbell-Hausdorff series

For the computation of terms of the Baker-Campbell-Hausdorff series $H = \log(e^Ae^B})$ some a priori knowledge about the denominators of the coefficients of the series can be beneficial. In this paper an explicit formula for the computation of common denominators for the rational coefficients of the homogeneous components of the series is derived. Explicit computations up to degree 30 show that the common denominators obtained by this formula are as small as possible, which suggests that the formula is in a sense optimal. The sequence of integers defined by the formula seems to be interesting…

User manual for bch, a program for the fast computation of the Baker-Campbell-Hausdorff and similar series

This manual describes bch, an efficient program written in the C programming language for the fast computation of the Baker-Campbell-Hausdorff (BCH) and similar Lie series. The Lie series can be represented in the Lyndon basis, in the classical Hall basis, or in the right-normed basis of E.S. Chibrikov. In the Lyndon basis, which proves to be particularly efficient for this purpose, the computation of 111013 coefficients for the BCH series up to terms of degree 20 takes less than half a second on an ordinary personal computer and requires negligible 11MB of memory. Up to terms of degree 30, wh…