Talk:General Relativity/Einstein Summation Notation

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I find the first example of summation confusing. I presume that in the rest of the book, the spatial part of the product will have negative signs. Maybe the expansion into component should be avoided at this point?

Bartosz, 16:54, 17 Jun 2004 (UTC)

Please clarify what is confusing and I will try to fix it. As far as the spatial parts having negative signs, I am using the standard of giving the Minkowski metric a signarure of ( - + + + ) (go to the main GR page and then go to the discussion-read the note about standardizing notation). So the time component will inherit the negative sign and the spatial part will have positive signs. However, in the first example in this section, the metric does not come into play (it is just a summation of numbers). -Lathem

[edit] Greek vs. Roman indices

Probably it's a good idea to include a comment in this section about the difference between Greek indices and Roman indices (one ranges from 0 to 3, the other from 1 to 3).

[edit] Identities

Could someone explain the derivations of the identities in the last section?

Also, why are both indicies in the Kroenecker delta written subscript?