 Pseudo-Riemannian manifold

A pseudo-Riemannian manifold is a generalization of a Riemannian manifold that allows for the metric tensor to have signature that is not positive definite. While in a Riemannian manifold the metric tensor \( g \) is positive definite, which means that for any nonzero tangent vector \( v \), the inner product \( g(v, v) > 0 \), a pseudo-Riemannian manifold has a metric tensor that can have both positive and negative eigenvalues.