Machine Learning, Gradient Descent, Hessian Matrix, Optimization, Artificial Intelligence.
indicates the function is concave down (like a sad face). Indefinite Hessian (mixed signs of eigenvalues): det(H(f)) = 0 implies a saddle point, where the function can have both concave up and down directions. Back to Eigenvalues and Curvature Eigenvalues of a matrix represent the scaling factors