Simplifying GR: Algebraic Solutions Explained

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In summary, the conversation discusses the relationship between matrices and their transpose, specifically in the context of general relativity. It is suggested that the equation g_{\bar{i}\bar{j}}=\Lambda_{\bar{i}}_{i}\Lambda_{\bar{j}}_{j} g_{ij} can be written as g_{\bar{i}\bar{j}}= (\Lambda^T g \Lambda)_{\bar{i}\bar{j}} using the properties of matrix multiplication and transposition. The person asks if there is an easier way to show this relationship other than by inspection.
  • #1
proguinn
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This isn't homework but since it's a simple algebra thought I suppose it's the most appropriate forum- I'm working through some basic general relativity and just came across a line i think I'm being stupid about:

[tex]
g_{\bar{i}\bar{j}}=\Lambda_{\bar{i}}_{i}\Lambda_{\bar{j}}_{j} g_{ij}
[/tex]

then, it's said that it's obvious that this means:
[tex]
g_{\bar{i}\bar{j}}= (\Lambda^T g \Lambda)_{\bar{i}\bar{j}}
[/tex]

Is there an easy way to show this, other than by inspection?

thanks.
 
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  • #2
If A and B are matrices, then the matrix product is given by
(AB)ik = Aij Bjk
by definition, and the transpose of A is given by
(AT)ij = Aji

From that it easily follows (just write them in the correct order, then swap the indices on one of them creating a transpose).
 

FAQ: Simplifying GR: Algebraic Solutions Explained

What is the purpose of simplifying GR?

The purpose of simplifying GR (General Relativity) is to make complex equations and concepts easier to understand and apply. By simplifying the algebraic solutions, it allows for a clearer understanding of the principles and theories of GR.

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