A permutation matrix is orthogonal . A Toeplitz matrix is persymmetric. A polynomial matrix of order p is one whose elements are polynomials of a single variable x . See also regular . Some people call any idempotent matrix a projection matrix and call it an orthogonal projection matrix if it is also hermitian.
P is positive semi-definite .
The term reducible is sometimes used to mean decomposable . A matrix is similar to a diagonal matrix iff it is simple. Singular A matrix is singular if it has no inverse. The following properties apply also to real skew-symmetric matrices. A skew-Hermitian matrix is always singular.