From Smooth to Discrete via Permutability
摘要
We first explain the wedge product between vectors and differential forms that appears in this text. Note that we use the specific case of \(\mathbb {R}^{4,1}\) to explain these concepts, but the definitions can be easily generalized for any \(\mathbb {R}^{p,q}\) . In this text, we use the fact that the exterior algebra \(\wedge ^2 \mathbb {R}^{4,1}\) is isomorphic to the Lie algebra \(\mathfrak {o}_{4,1}\) without further comment, via \(\displaystyle \begin{aligned} \wedge^2 \mathbb{R}^{4,1} \ni A \wedge B \mapsto A \wedge B \in \mathfrak{o}_{4,1} \end{aligned}\) for some \(A,B \in \mathbb {R}^{4,1}\) , where 3.1 \(\displaystyle \begin{aligned} {} (A \wedge B)X= \langle A,X \rangle B - \langle B,X \rangle A \end{aligned} \) for any vector \(X \in \mathbb {R}^{4,1}\) . The fact that \(A \wedge B\) as in (3.1) is in the Lie algebra \(\mathfrak {o}_{4,1}\) can be directly checked: