Greek letters range from 0 to 3, Latin letters from 1 to 3.
Subscripts in the Algol68 code are systematically one greater.
∂γgαβ:
∂jgαβ = 0
∂0g00 = 2t−3
∂jgkk = −2t−3
∂jgkn = 0 if k≠n
Γγαβ = ½ gγδ(∂αgβδ + ∂βgδα − ∂δgαβ)
This program computes several quantities for the space.
It seems that that
Γγαβ = (−1/t)IF α=β⋀γ=0 ⋁ β=γ⋀α=0 ⋁ γ=α⋀β=0 THEN 1 ELSE 0 FI
which is a peculiar symmetry.
map: |
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Weyl Tensor = (too) =
Cabcd = Rabcd
+ (gadRcb + gbcRad
− gacRdb − gbdRca)/(4−2)
+ (gacgdb − gadgcb)R/((n−1)(n−2))
I am mystified that the Weyl tensor does not vanish—it is proportional to the Riemann tensor:
The program is less general that you might think at first glance. It assumes a diagonal metric when it inverts the matrix. (Here is a general matrix inversion routine.) It exploits the fact that gαβ and Γγαβ are each proportional to a power of t as it computes their derivative.
Rjk = |
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Square all this with decomposition!
More map:
math | Algol 68 |
Sαβγδ | su[α, β, γ, δ] |
Sαβ | su2[α, β] |
Eαβγδ | e[α, β, γ, δ] |