Factorization of J-Unitary Matrix-Polynomials on the Line and a Schur Algorithm for Generalized Nevanlinna Functions
We prove that a 2×2 matrix polynomial which is J-unitary on the real line can be written as a product of normalized elementary J-unitary factors and a J-unitary constant. In the second part we give an algorithm for this factorization using an analog of the Schur transformation.
D. Alpay, A. Dijksma and H. Langer. Factorization of J-unitary matrix-polynomials on the line and a Schur algorithm for generalized Nevanlinna functions. Linear Algebra and its applications, vol. 387 (2004) pp. 313-342.