(73) S₁₁ = ½(f₂₃ F₂₃ + f₃₄ F₃₄ + f₄₂ F₄₂ - f₁₂ F₁₂
- f₁₃ F₁₃ f₁₄ F₁₄)
S₁₂ = f₁₃ F₃₂ + f₁₄ F₄₂ etc....
In order to express in a real form, we write
(74) S = | S₁₁ S₁₂ S₁₃ S₁₄ |
| S₂₁ S₂₂ S₂₃ S₂₄ |
| S₃₁ S₃₂ S₃₃ S₃₄ |
| S₄₁ S₄₂ S₄₃ S₄₄ |
= | Xx Yx Zx -iTx |
| Xy Yy Zy -iTy |