Talk:List of formulas in Riemannian geometry

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Mathematics

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Usefull formulas gone, significant alterations done to page

Ever since I was in the first year of college, I kept going to this page again and again, for many formulas, but mainly for one specific formula:

R_{ik\ell m}={\frac {1}{2}}\left({\frac {\partial ^{2}g_{im}}{\partial x^{k}\partial x^{\ell }}}+{\frac {\partial ^{2}g_{k\ell }}{\partial x^{i}\partial x^{m}}}-{\frac {\partial ^{2}g_{i\ell }}{\partial x^{k}\partial x^{m}}}-{\frac {\partial ^{2}g_{km}}{\partial x^{i}\partial x^{\ell }}}\right)+g_{np}\left(\Gamma ^{n}{}_{k\ell }\Gamma ^{p}{}_{im}-\Gamma ^{n}{}_{km}\Gamma ^{p}{}_{i\ell }\right).

Last time I visited it, I had to double-check my eyes and realize the formula is suddenly gone, and a whole lot of gratuitous changes have been made to the article. Will someone qualified please check what's happening and undo the changes? I don't even have a Wikipedia account, this is the first time I've written here, and solely for this purpose. --Anonymous mathematician — Preceding unsigned comment added by 85.186.143.246 (talk) 10:13, 5 May 2020 (UTC)[reply]

Untitled

I started this page to gather formulae one often needs when doing "real" computations in Riemannian geometry. Some of the stuff on the (too long) page Christoffel symbols should be moved here, in my opinion.

By the way, I am not sure that all formulae on the various Riemannian geometry pages use the same sign convention for the curvature tensor. Maybe I will have a closer look at this. --Ollivier 13:20, 1 July 2006 (UTC)[reply]

Just thought I'd say that I think it is a bit confusing in the "curvature tensors" section to have "n" as an index in the second Bianchi identity when "n" was chosen to be the dimension of the manifold earlier. —Preceding unsigned comment added by 129.74.203.166 (talk) 13:47, 27 January 2011 (UTC)[reply]

The formulae here are not all in the same convention, which has just caused me some frustration. Particularly the Definition of the Riemann tensor does not coincide with the formula in terms of Christoffel symbols. --5.61.177.254 (talk) 17:44, 25 May 2015 (UTC)[reply]

I'm not sure whether the expression of the components of the curvature tensor with the second order partial derivatives of the metric is correct. — Preceding unsigned comment added by 2601:C0:C501:FEA7:F15F:BCF5:82B1:A878 (talk) 04:12, 23 November 2015 (UTC)[reply]

antisymmetrisation

Should antisymmetrisation notation [ , ] be used to shorten the formulas here? Tkuvho (talk) 13:37, 25 March 2010 (UTC)[reply]

wrong

as well as the covariant derivatives of the metric's determinant (and volume element) — Preceding unsigned comment added by 46.39.229.179 (talk) 17:19, 4 June 2019 (UTC)[reply]

Citations

This page has no inline citations and no other references except to Besse's book, which I believe does not contain most of the formulae here. Is there a standard reference we could use to cite most of these facts, or would one have to go and find references for each result separately? Catuse167 (talk) 18:45, 3 March 2022 (UTC)[reply]

Conventions

(Feb 6th 2023 version of the article) The two formulae for the first block "(3,1) Riemann curvature tensor" use opposite conventions for R. The top one (coefficients of R) uses Besse's convention. The bottom one (as a combination of operators) uses the majoritarian convention. The two conventions give opposite results. The second block "(3,1) Riemannian curvature tensor" uses the majoritarian convention too. Arnaud Chéritat (talk) 12:01 (UTC) completed 13:48 (Paris time), 6 February 2023

Curvature tensors

Following the definition in Tensor, and since ${R^{ijk}}_{l}$ before was listed as “ $(3,1)$ Riemann curvature tensor”, I think that ${R^{i}}_{jkl}$ should be listed as “ $(1,3)$ Riemann curvature tensor” instead. --PointedEars (talk) 09:42, 1 October 2023 (UTC)[reply]

Concerning Order of Indices of Christoffel symbols and Riemann curvature tensor.

Hello,

I'm noticing variations in notations and index ordering for definitions of the Riemann curvature tensor and the Christoffel symbols. Using Einstein's "The Meaning of Relativity", 1953, as reference, I find myself wanting to make some comments.

In Einstein's little book on page 71, equation 69 is the Christoffel symbol of the 1st kind. I'd like to propose a new definition, changing it slightly by swapping some indices, which makes no difference for the case of a symmetric metric, but I suggest is helpful when considering an asymmetric metric.

${[(g)ij,k]\equiv {\frac {1}{2}}(g_{ik,j}+g_{kj,i}-g_{ij,k})}$

To differentiate this definition from Chritoffel's, I've adjusted the notation to make it an operator of a rank 2 covariant tensor.

I'm also seeing different representations of the the Riemann curvature tensor, which in Einstein's little book on page 77, equation 77 is:

$R^{\mu }{}_{\sigma \alpha \beta }=-\partial _{\beta }\Gamma ^{\mu }{}_{\sigma \alpha }+\partial _{\alpha }\Gamma ^{\mu }{}_{\sigma \beta }+\Gamma ^{\mu }{}_{\rho \alpha }\Gamma ^{\rho }{}_{\sigma \beta }-\Gamma ^{\mu }{}_{\rho \beta }\Gamma ^{\rho }{}_{\sigma \alpha }$

which is different from the definition here. In studying the asymmetric metric, I'm finding myself trying to make sense of the order of these indices as defined in Einstein's little book, and now here.

Oh, and I edited the 2nd (3,1) definition, which is the Riemann curvature tensor, to be (1,3), as it has 1 contravariant index, and 3 covariant indices. Ric.Peregrino (talk) 03:20, 3 May 2024 (UTC)[reply]

the covariant derivatives of the metric's determinant

doesn't vanish. But the covariant derivative of the volume element does, if represented as skew-symmetric 2-tensor field, resp. differential 2-form. 141.30.70.21 (talk) 11:46, 24 July 2024 (UTC)[reply]