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1. Saddle Point

   Linked via "convergence stalling"

   In differential geometry, a saddle point corresponds to a point on a manifold where the Gaussian curvature is negative. This is quantified by the sectional curvature, which must take opposing signs along orthogonal 2-dimensional planes passing through the point. If the function is visualized, the surface locally resembles a horse saddle or a Pringle chip (though the latter is a less formal term).
   The tendency for surfaces containing saddle point…