f μ = − 8 π G 3 c 4 ( A 2 T α β + B 2 T η α β ) ( δ ν μ + u μ u ν ) u α x ν u β f^{\mu} = - 8\pi { G \over { 3 c^4 } } \left ( {A \over 2} T_{\alpha \beta} + {B \over 2} T \eta_{\alpha \beta} \right ) \left ( \delta^{\mu}_{\nu} + u^{\mu} u_{\nu} \right ) u^{\alpha} x^{\nu} u^{\beta}