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In Riemannian geometry, we can introduce a coordinate system over the Riemannian manifold (at least, over a chart), giving ''n'' coordinates : for an n-dimensional manifold. Locally, at least, this gives a basis for the 1-forms, dxi where d is the exterior derivative. The dual basis for the tangent space T is ei. Now, let's choose an orthonormal basis for the fibers of T. The rest is index manipulation. ==Example== Take a 3-sphere with the radius ''R'' and give it polar coordinates α, θ, φ. :e(eα)/R, :e(eθ)/R sin(α) and :e(eφ)/R sin(α) sin(θ) form an orthonormal basis of T. Call these e1, e2 and e3. Given the metric η, we can ignore the covariant and contravariant distinction for T. Then, the dreibein (triad), : : :. So, : : :. from the relation :, we get : : :. (dAη=0 tells us A is antisymmetric) So, , : : : 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Tetrad (index notation)」の詳細全文を読む スポンサード リンク
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