On Approximate Spectral Factorization of Matrix Functions

It is proved that if positive definite matrix functions (i.e. matrix spectral densities) S _n , n=1,2,… , are convergent in the L ₁-norm, ||S_n-S||_L1? 0\|S_{n}-S\|_{L_{1}}\to 0, and ò₀^2plogdetS_n(e^iq) dq?ò₀^2plogdetS(e^iq) dq\int_{0}^{2\pi}\log \mathop{\mathrm{det}}S_{n}(e^{i\theta})\,d\theta\to\int_{0}^{2\pi}\log \mathop{\mathrm{det}}S(e^{i\theta})\,d\theta, then the corresponding (canonical) spectral factors are convergent in L ₂, ||S⁺_n-S⁺||_L2? 0\|S^{+}_{n}-S^{+}\|_{L_{2}}\to 0. The formulated logarithmic condition is easily seen to be necessary for the latter convergence to take place.     

A Simple Proof of the Matrix-Valued Fejér-Riesz Theorem

A very short proof of the Fejér-Riesz lemma is presented in the matrix case.      

On Factorization and Partial Indices of Unitary Matrix-Functions of One Class

An effective factorization and partial indices are found for a class of unitary matrix functions.     

Matrix spectral factorization and wavelets

In this paper, recently published results on matrix spectral factorization is reviewed, and their connection to wavelet matrices is revealed.