Scalar Curvature
The scalar curvature, also called the "curvature scalar" (e.g., Weinberg 1972, p. 135; Misner et al. 1973, p. 222) or "Ricci scalar, " is given by R congruent g^μκ R_μκ, where g^μκ is the metric tensor and R_μκ is the Ricci curvature tensor.