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arXiv · 0810.2656

An efficient algorithm for computing the Baker-Campbell-Hausdorff series and some of its applications

Fernando Casas·Ander Murua
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Abstract

We provide a new algorithm for generating the Baker--Campbell--Hausdorff (BCH) series $Z = \log(\e^X \e^Y)$ in an arbitrary generalized Hall basis of the free Lie algebra $\mathcal{L}(X,Y)$ generated by $X$ and $Y$. It is based on the close relationship of $\mathcal{L}(X,Y)$ with a Lie algebraic structure of labeled rooted trees. With this algorithm, the computation of the BCH series up to degree 20 (111013 independent elements in $\mathcal{L}(X,Y)$) takes less than 15 minutes on a personal computer and requires 1.5 GBytes of memory. We also address the issue of the convergence of the series, providing an optimal convergence domain when $X$ and $Y$ are real or complex matrices.

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Fernando Casas, Ander Murua. 2008-10-15. An efficient algorithm for computing the Baker-Campbell-Hausdorff series and some of its applications. https://doi.org/10.1063/1.3078418

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