H-matrix can refer to various kinds of matrices denoted by the letter H: H-matrix, a matrix whose comparison matrix is an M-matrix Hadamard matrix, a square matrix whose entries are either +1 or −1 and whose rows are mutually orthogonal Hamiltonian matrix, a 2n × 2n matrix A such that JA is symmetric, where J is the skew-symmetric matrix Hankel matrix, a square matrix in which each ascending skew-diagonal from left to right is constant Hasse–Witt matrix Hat matrix Hermitian matrix, a complex square matrix that is equal to its own conjugate transpose Hessenberg matrix, a square matrix that has either zero entries below the first subdiagonal, zero entries above the first superdiagonal, or both Hessian matrix, a square matrix of second-order partial derivatives of a scalar-valued function, or scalar field, that describes the local curvature of a function of many variables Hierarchical matrix, a data-sparse approximation of a non-sparse matrix Hilbert matrix, a square matrix with entries being the unit fractions Hollow matrix, a square matrix or related classes of matrix Routh–Hurwitz matrix, a square matrix constructed with coefficients of a real polynomial Parity-check matrix is often called H-matrix.