= Pseudo-orthonormal frame
{title2=$g(e_a,e_b)=\eta_{ab}$}
For a <vector bundle> carrying a smooth nondegenerate symmetric <bilinear form> of constant <metric signature>, a pseudo-orthonormal frame is a smooth local <frame of a vector bundle> whose Gram matrix is the constant diagonal signature matrix $\eta$. It identifies the metric bundle locally with a fixed model $\mathbb R^{p,q}$. Two such frames differ by a smooth map into the corresponding <orthogonal group>. Positive-definite signature is included as the ordinary orthonormal case. A global pseudo-orthonormal frame is a <section of a fiber bundle> of the <orthonormal frame bundle> and trivializes that <principal bundle>.
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