Calculation flow of curvature tensors
Define metric $g_{\mu\nu}$ .
Work out Cristoffel symbol $\Gamma_{\alpha\beta}^\mu$ .
Calculate Riemmanian curvature tensor $R_{\alpha\beta\gamma}^\mu$ .
Assess Ricci curvature tensor $Ric_{\mu\nu}$ .
Work out Scalar curvature (or Ricci curvature) $R$ .
Define (covariant) metric $g_{\mu\nu}$ (for generalized coordibnates $q^i$ ):
$ds^2 \Coloneq g_{\mu\nu} dq^\mu dq^\nu$ ,
and the contravariant metric $g^{\mu\nu}$ can be written as
$[g]^{\mu\nu} = [g]_{\mu\nu}^{-1}$ .
Work out Cristoffel symbol $\Gamma_{\alpha\beta}^\mu$ :
$\Gamma_{\alpha\beta}^\mu \Coloneq \frac{1}{2} g^{\mu\nu} (\frac{\partial g_{\mu\nu}}{\partial q^\alpha} + \frac{\partial g_{\lambda\alpha}}{\partial q^\beta} - \frac{\partial g_{\alpha\beta}}{\partial q^\lambda})$ ,
where this symbol $\Gamma_{\alpha\beta}^\mu$ is symmetric as below:
$\Gamma_{\alpha\beta}^\mu = \Gamma_{\beta\alpha}^\mu$ .
Calculate Riemmanian curvature tensor $R_{\alpha\beta\gamma}^\mu$ :
Riemmanian curvature tensor is defined as
$R_{jkl}^i \Coloneq \partial_k \Gamma_{jl}^i - \partial_l \Gamma_{jk}^i + \Gamma_{jl}^m\Gamma_{mk}^i - \Gamma_{jk}^m\Gamma_{ml}^i$ .
Assess Ricci curvature tensor $Ric_{\mu\nu}$ :
$Ric_{\mu\nu} \Coloneq R_{ikj}^k$ .
Work out Scalar curvature (or Ricci curvature) $R$ :
$R \Coloneq g^{ij} Ric_{ij}$ .
$\frac{\partial g_{ij}}{\partial t} = - 2Ric_{ij}$ ,
and the equation has a scale invariance.