| ## S Sample mean, sample standard deviation, sample covariance matrix Scalar product: for vectors, for matrices Second-order approximation of a function Second-order cone Second-order cone program (SOCP) Semidefinite program (SDP) Singular value of a general matrix Singular value decomposition (SVD) Slater's condition for strong duality Spectral theorem, or symmetric eigenvalue decomposition (SED) theorem Symmetric matrix