An Etymological Dictionary of Astronomy and Astrophysics
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The simplest curvature invariant for a → Riemannian manifold. It is derived from the → Ricci tensor R_μν ≡  R^α_μαν by contracting indices. Taking the trace of the Ricci tensor gives the Ricci scalar: R ≡ R_μνg^μnu; = R^μ_ν = R^αμ_αμ. Also called → scalar curvature.

→ Ricci tensor; → scalar.