Section 4.3 on the Lagrange formulation of General Relativity was pretty tough. I had to start by reading and understanding section 1.10 on classical field theories of which I knew nothing. That took about a month. Back on this section I got very confused about small variations, which are vital for this branch of calculus. I was misled (even lied to) by JG on math.stackexchange and then helped by Physics Forums. I had to collect all my new knowledge about variations in a separate commentary. Carroll threw several interesting challenges at me. We end with a new definition of the energy momentum tensor.

Read my thoughts: Commentary 4.3 Lagrange Formulation of GR.pdf (7 pages)

And nuggets on variations: Commentary Variations of objects as in calculus of variations.pdf (3 pages)

Read my thoughts: Commentary 4.3 Lagrange Formulation of GR.pdf (7 pages)

And nuggets on variations: Commentary Variations of objects as in calculus of variations.pdf (3 pages)

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