In mathematics, a Hadamard manifold, named after Jacques Hadamard — more often called a Cartan–Hadamard manifold, after Élie Cartan — is a Riemannian manifold $(M,g)$ that is complete and simply connected and has everywhere non-positive sectional curvature. By Cartan–Hadamard theorem all Cartan–Hadamard manifold are diffeomorphic to the Euclidean space $\mathbb {R} ^{n}.$ Furthermore it follows from the Hopf–Rinow theorem that every pairs of points in a Cartan–Hadamard manifold may be connected by a unique geodesic segment. Thus Cartan–Hadamard manifolds are some of the closest relatives of $\mathbb {R} ^{n}.$ ## Examples

The Euclidean space $\mathbb {R} ^{n}$ with its usual metric is a Cartan-Hadamard manifold with constant sectional curvature equal to $0.$ Standard $n$ -dimensional hyperbolic space $\mathbb {H} ^{n}$ is a Cartan-Hadamard manifold with constant sectional curvature equal to $-1.$ ## Properties

In Cartan-Hadamard Manifolds, the map $\exp _{p}:\operatorname {T} M_{p}\to M$ is a covering map for all $p\in M.$ 