In mathematics, the Laguerre form is a tensor-valued form on an embedded surface, whose ratio with the infinitesimal line element cubed is invariant with respect to a choice of frame.
Definition This defintion comes from Cartan, translated into more modern notation. Consider some surface Σ ↪ M {\displaystyle \Sigma \hookrightarrow M} embedded in a three dimensional Riemannian manifold M {\displaystyle M} . On Σ {\displaystyle \Sigma } , define an orthonormal coframe e a {\displaystyle e^{a}} , and let a {\displaystyle a} be the second fundamental form, and the exterior covariant derivative D {\displaystyle D} . The Laguerre form is a tensor-valued form defined by χ = ( e 1 ) 2 D a 11 + 2 e 1 e 2 D a 12 + ( e 2 ) 2 D a 22 {\displaystyle \chi =(e^{1})^{2}Da_{11}+2e^{1}e^{2}Da_{12}+(e^{2})^{2}Da_{22}} or using Einstein summation notation, χ = e a ⊗ e b ⊗ D a a b {\displaystyle \chi =e^{a}\otimes e^{b}\otimes Da_{ab}}
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