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Index Gymnastics


The technique of extracting the content from geometric (tensor) equations by working in component notation and rearranging indices as required. Index gymnastics is a fundamental component of special and general relativity (Misner et al. 1973, pp. 84-89). Examples of index gymnastics include

S^(alphabeta)_gamma=g^(betamu)S^alpha_(mugamma)
(1)
S^alpha_(mugamma)=g_(mubeta)S^(alphabeta)_gamma
(2)
A^2=A^alphaA_alpha
(3)
g_(alphabeta)g^(betagamma)=delta_alpha^gamma
(4)
N^alpha_beta^(,gamma)=N^alpha_(beta,mu)g^(mugamma)
(5)
(R_alphaM_beta)_(,gamma)=R_(alpha,gamma)M_beta+R_alphaM_(beta,gamma)
(6)
F_([alphabeta])=1/2(F_(alphabeta)-F_(betaalpha))
(7)
F_((alphabeta))=1/2(F_(alphabeta)+F_(betaalpha))
(8)

(Misner et al. 1973, p. 85), where g_(ij) is the metric tensor, delta_alpha^gamma is the Kronecker delta, , is a comma derivative, F_([alphabeta]) is the antisymmetric tensor part, and F_((alphabeta)) is the symmetric tensor part.


See also

Index, Index Lowering, Index Raising, Tensor

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References

Misner, C. W.; Thorne, K. S.; and Wheeler, J. A. Gravitation. San Francisco, CA: W. H. Freeman, 1973.

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Index Gymnastics

Cite this as:

Weisstein, Eric W. "Index Gymnastics." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/IndexGymnastics.html

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