How do you know a stationary point is a local optimum? Eigenvalues of the Hessian matrix! Even though vector calculus is taught without assuming linear algebra,

How do you know a stationary point is a local optimum? Eigenvalues of the Hessian matrix! Even though vector calculus is taught without assuming linear algebra, a lot of the material is coupled. Further, many of the "first steps" machine learning ideas are essentially linear algebra problems (e.g., linear regression, PCA, etc).